This article was downloaded by: [Case Western Reserve University]On: 24 November 2014, At: 13:08Publisher: RoutledgeInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

MemoryPublication details, including instructions for authors and subscriptioninformation:http://www.tandfonline.com/loi/pmem20

A re-evaluation of the phonologicalsimilarity effect in adults' short-termmemory of words and nonwordsArild Lian a , Paul J. Karlsen a & Bendik Winsvold aa University of Oslo, NorwayPublished online: 22 Sep 2010.

To cite this article: Arild Lian , Paul J. Karlsen & Bendik Winsvold (2001) A re-evaluation of thephonological similarity effect in adults' short-term memory of words and nonwords, Memory, 9:4-6,281-299, DOI: 10.1080/09658210143000074

To link to this article: http://dx.doi.org/10.1080/09658210143000074

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis, ouragents, and our licensors make no representations or warranties whatsoever as to theaccuracy, completeness, or suitability for any purpose of the Content. Any opinions andviews expressed in this publication are the opinions and views of the authors, and are notthe views of or endorsed by Taylor & Francis. The accuracy of the Content should not berelied upon and should be independently verified with primary sources of information. Taylorand Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs,expenses, damages, and other liabilities whatsoever or howsoever caused arising directly orindirectly in connection with, in relation to or arising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any substantialor systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply,or distribution in any form to anyone is expressly forbidden. Terms & Conditions of accessand use can be found at http://www.tandfonline.com/page/terms-and-conditions

A re-evaluation of the phonological similarity effect inadults’ short-term memory of words and nonwords

Arild Lian, Paul J. Karlsen, and Bendik Winsvold

University of Oslo, Norway

The phonological similarity effect (PSE) was studied in two tasks of serial recall, in one task of serialrecognition and one item identification task. PSE occurred only in the former three tasks involvingmemory of order when study items were words and nonwords with an associative connectedness to long-term memory. Nonwords that, according to a reaction time assessment of associative value, were less wellconnected to long-term memory mechanisms, were not sensitive to phonological similarity. These resultsare discussed in relation to contemporary models of short-term memory that explain the PSE as a result ofconfusions of items that are similarly encoded in a phonological layer. This layer is identified as a higher-level phonological space that is accessed by words and nonwords of high associative value and not bynonwords of low associative value.

In immediate serial recall tasks, lists of verbalitems that are phonologically similar are typicallyrecalled less well than lists of phonologically dis-tinct items. This means that the list mad, cap, cat isusually more difficult to remember than the listcow, bar, pen. This has been called the phonolo-gical similarity effect (PSE). It was first reportedby Conrad and Hull (1964) and has since beenextensively explored in the literature of verbalshort-term memory (Baddeley, 1966; Conrad,1964; Estes, 1973; Longoni, Richardson, & Aiello,1993; Murray, 1968; Salame & Baddeley, 1986;Wickelgren, 1965). Nairne (1990) brands PSE as abenchmark fact of that literature; Gathercole(1997) identifies it as one of five key empiricalfindings that any plausible model of short-termmemory must explain; Page and Norris (1998)state the explanation of PSE as an essential test ofsuch models.

The initial problem of our study applies to thegenerality of PSE. In most earlier works on short-term memory, items to be remembered werefamiliar words, digits, or single letters. For literate

adults these materials generally form well-knownsound patterns with specific representations atlexical and semantic levels in long-term memory.How is the memory of unfamiliar speech soundpatterns affected by manipulation of the phono-logical similarity of the material to be remem-bered? In the present work we raise the problemof whether PSE applies to both words and non-words with differing associative values. This is anew concept based on an independent and open-ended reaction time test introduced in our study.This initial test makes it possible to distinguishbetween the associative values of individual wordsand nonwords by measuring how fast subjectscome up with associations to each of these utter-ances. The pretest makes up an effective tool indefining our stimulus material and is thoroughlydiscussed later.

The PSE was studied in two tasks of serialrecall, in one task of serial recognition, and oneitem identification task. Brown (1997) distin-guishes between the memory for individual itemsand the memory for serial order of these items. He

MEMORY, 2001, 9 (4/5/6), 281–299

# 2001 Psychology Press Ltdhttp://www.tandf.co.uk/journals/pp/09658211.html DOI:10.1080/09658210143000074

Requests for reprints should be sent to Arild Lian, Institute of Psychology, Box 1094, Blindern, N-0317 Oslo, Norway. Email:arild.lian@psykologi.uio.no

The authors gratefully acknowledge the assistance of Marte Mengshoel Linnae and Per Magne Nilsen for running the experimentsand for examining the speech sound files. This work was supported in part by a grant from the Norwegian Research Council to the firstauthor.

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

claims that any recall task makes demands on bothsorts of memory. Some studies indicate that PSE ismainly associated with confusion of serial order,or transpositions among the phonologically simi-lar items in the list (Conrad, 1965; Drewnowski,1980; Ellis, 1980; Healy, 1974; Murdock & vomSaal, 1967; Wickelgren, 1965). Item errors—likeomissions, repetitions, missed repetitions, andintrusions—do not increase to the same extent.How is the memory of unfamiliar speech soundsaffected in tasks that focus especially on memoryof order and memory of items respectively, com-pared to the memory of words and familiar speechsounds in the same tasks? We look into that in theserial recognition task and the item identificationtask in Experiment 2.

The classical explanation of PSE involves aninterference interpretation and has been adoptedby all models that explicitly deal with PSE. Atwhat specific level or layer of representation dothe assumed interferences or confusions betweenphonologically similar items occur? If PSE isgrounded on a confusion of phonologically similaritems causing transition errors during serial recall,it might be claimed that it should apply equallywell to words and nonwords, regardless of theirassociative value, as the phonological level ofrepresentation may be assumed to be the same forany verbal material auditorily encoded. Based onthe interference interpretation, it might even beclaimed that PSE should be stronger for nonwordsthan for words. As unfamiliar nonwords maydepend to a lesser extent than words on semanticor lexical long-term representations, it is reason-able to think that the encoding of unfamiliarnonwords is more dependent on acoustic orphonological features than the encoding offamiliar words. The fact that the activation ofthese features may also be less stable for non-words than for words, should make them espe-cially vulnerable to random decay and followingconfusion.

Any robust differences in the way familiar andunfamiliar speech sound patterns are affected byphonological similarity, then, may give us valuableinformation about how verbal material is dealtwith in short-term memory. Some phonologicalrepresentation level is assumed to be active forany verbal material, independent of the semanticmeaningfulness, or association value, of thematerial to be remembered. PSE may be assumedto be a result of confusion of items at that level. Asa result of our study, however, it seems necessaryto distinguish between different levels or layers of

phonological representation. The classical PSEseems to be a result of confusion in a late, lexicallayer that is highly activated or accessed by themore familiar speech sounds. Confusions at thislevel may involve clusters of phonological seg-ments already represented in long-term memoryand that are associated with meaningful material.

MODELS AND BACKGROUND DATA

How has PSE been dealt with so far in the lit-erature? In her 1997 article, Gathercole surveysfour major contemporary models of short-termmemory and finds that none of them sufficientlyexplains PSE. The models are the phonologicalloop (Baddeley, 1986), the network model of thephonological loop (Burgess & Hitch, 1992), thetrace decay model (Brown & Hulme, 1995), andthe interactive model (Gathercole & Martin,1996). The former two seem to be the only ones tohave addressed the problem directly. As Brownand Hulme acknowledge, their 1995 model isunable to accommodate the PSE, as it does not‘‘represent’’ the phonological structure of amemory item in any way other than the amount oftime it occupies, and as the interactive model isnot explicit on the issue of how the serial order ofactivated phonological elements is represented, ittoo provides no explanation for the disruptiveeffects of phonological similarity betweenmemory items.

Baddeley’s phonological loop comprises twocomponents, the phonological short-term storeand the subvocal rehearsal process. The phono-logical store represents the material in a phono-logical code that decays with time. A process ofarticulatory-like rehearsal serves to refresh thedecaying representations in the phonological storeand so to maintain the memory items. Accordingto the phonological loop model, the source of PSEin immediate serial recall is the phonologicalstore. It is argued that memory items that share asimilar phonological structure will become morerapidly indiscriminable from one another due todecay than items with non-overlapping phono-logical structures (Baddeley, 1986). In the net-work model of the phonological loop, thesimilarity effect is due to the operation of thefeedback weights running from the outputphoneme layer to the input phoneme layer, asthese weights implement the phonological store inthe model (Burgess & Hitch, 1992, 1999).

As information in the phonological store

282 LIAN, KARLSEN, WINSVOLD

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

decays, it needs to be reconstructed throughrehearsal. The reconstruction is assumed todepend on some other information that has notbeen subject to the same speed of decay. Thisinformation is presumably lexical long-termmemory representations that were somewhatactivated by the original presentation of thememory list.

According to some researchers, a controlledrehearsal process is not necessary for the recon-struction of decayed information. Instead, aredintegration process has been postulated, akin topattern completion in speech perception (Brown &Hulme, 1995; Schweickert, 1993). This process wassaid to depend on lexical long-term representationsin the phonological form of words, a representationthat is supposed to be generally lacking for non-words (Hulme, Newton, Cowan, Stuart, & Brown,1999). This redintegration process, then, accountsfor the lexicality and the word familiarity effect. Assome nonwords may activate long-term repre-sentations, the redintegration process may alsoaccount for the wordlikeness effect. If phonologicalinformation in short-term memory generallydecays with the same speed, and the phonologicalredintegration process is not activated, thereshould be no PSE, and very low recall span.

Another model of interest here is Nairne’s(1990) feature model of immediate memory. Thismodel involves another disadvantage interpreta-tion of phonologically similar items, in the sensethat long-term representations of items that shareone or more vowels are assumed to contain manyoverlapping features. If features or lower-levelsegments of an item in short-term memory havebeen overwritten or forgotten, a matching processsimilar to redintegration occurs. Again, an item islikely to be confused with other items in a list ifthey have confusable long-term representations. Ifthere were hardly any long-term lexical repre-sentations activated by certain lists of nonwords,there should be a clear lexicality effect whencompared to words, and there should be nothingto confuse; that is, no PSE for nonwords comparedto words, or an interaction effect between lexi-cality and phonological similarity.

Schweickert (1993) postulates two parallelredintegration processes: one that attempts toform a word, and another that attempts to form aphoneme string. According to Schweickert, thetwo processes are autonomous and can be selec-tively influenced by lexicality and phonologicalsimilarity. Schweickert predicts that there shouldbe no interaction between phonological similarity

and lexicality: he sees that as a necessary impli-cation of the two mechanisms being autonomous.An experiment by Besner and Davelaar (1982) istaken to be in agreement with this prediction. Inour view, however, it is not necessary to postulatetwo parallel redintegration processes to accountfor the PSE, the lexicality effect, and the lack of aninteraction between the two found in Besner andDavelaar’s experiment.

Besner and Davelaar (1982) demonstrated thatthe phonemically similar lists were less accuratelyrecalled than lists of phonemically distinct items,irrespective of the wordlikeness of the visuallypresented materials. This finding disagreed withthe results of a pilot experiment with 18 subjectsrun in our laboratory. The pilot experimentinvolved a serial recall task almost identical to thatreported in our Experiments 1A and 1B, exceptthat the earlier stimulus material was not assessedfor associative values. We found, in agreementwith both Besner and Davelaar (1982) and Hulmeet al. (1999), that memory span is substantiallylonger for words than nonwords. However, ourresults also showed a significant interaction effectbetween lexicality and phonological similarity,indicating in our case that the phonological simi-larity factor affected words but not nonwords. Thereason why the results of our pilot experimentdiffered from those of Besner and Davelaar’s(1982) experiment may be that we made use ofauditory representation. That would indicate amodality effect. Also, the vowels in Besner andDavelaar’s items seem to be of longer durationthan ours, indicating a possible vowel durationeffect. The difference observed between the twoexperiments could also be the result of Besner andDavelaar’s less wordlike nonwords being insuffi-ciently unwordlike.

Hulme (1984) and Hulme and Tordoff (1989)found an interesting interaction between the sizeof PSE and age for immediate serial recall ofwords. The growth of memory span with age wasattributed to the increasing number of distinctwords being recalled; the number of similar wordsrecalled showed very little growth with age. Whenspeech rate was controlled for, the effect of agewas no longer significant. A new interpretation ofthis result in line with our study would be that theincrease in speech rate and PSE are both asso-ciated with growth of vocabulary and thedevelopment of the lexical phonological layer.

More recently, Gathercole, Pickering, Hall,and Peaker (2001) have compared degrees ofsensitivity to phonological similarity for words and

EFFECTS OF PHONOLOGICAL SIMILARITY 283

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

nonwords in two experiments on serial recall andtwo experiments on serial recognition. All itemswere one-syllable consonant-vowel-consonant s(CVCs) drawn from a pool of 150 words and 150nonwords. The phonologically similar lists weremade up of items that had different consonantsbut shared a vowel, and in the phonologicallydistinct list all vowels were different. These non-words seem rather similar to the ones used in ourexperiments. Another point of convergence wasthe use of auditory presentation.

The two serial recall experiments (Experiment3A with children and Experiment 4A with adultsubjects) demonstrated a significant interactioneffect between lexicality (words vs nonwords) andphonological similarity (phonologically similar vsdistinct lists) showing that the sensitivity tophonological similarity is higher for words thanfor nonwords. Also, in the serial recognitionexperiments the difference in scores betweensimilar and distinct lists was greater for words thannonwords, but the interaction between the twofactors was not significant. Gathercole et al.’s(2001) data, then, indicate that PSE is higher forwords than nonwords in serial recall but not inserial recognition tasks.

Nonwords that are wordlike and more likely toactivate lexical long-term memory representa-tions may be more sensitive to phonologicalsimilarity compared to nonwords that are lesswordlike and more or less meaningless items forthe participating subjects. It may be that thesetypes of nonwords activate lexical layers to agreater extent than unwordlike nonwords, but alsothat they do not activate semantic layers to thesame extent as words. Wordlike nonwords, then,may be especially vulnerable to phonologicalsimilarity. Therefore, Gathercole et al.’s (2001)demonstration of a significant interaction effectbetween lexicality and phonological similarity intwo out of four experiments may depend on theselection of nonword items for the four experi-ments. In the present work we shall re-examinethis issue by studying PSE for both words andnonwords in serial recall and serial recognitiontasks while taking into consideration the associa-tive values among the items.

THE PRETEST

The aim of the pretest is to separate items thathave the lexical status of nonwords but arewordlike and likely to produce some long-term

association when spoken to language-competentadult listeners, and nonword items that are lesslikely to call forth any long-term association byadults. To categorise items in respect to mean-ingfulness or associative value, a rating task couldbe used, in which case judgements of, say, word-likeness are done without any time constraint.However, the encoding of items in serial recall andserial recognition experiments will take placeunder some time constraint. Items in the list can-not be studied for an unlimited time. They arepresented successively at a certain time rate, witha short pause between each item, giving little timefor associative processes and rehearsal. Also, theyare usually presented only once. During the recallstage there may be less time constraints as subjectsare usually told that they may recall items at theirown pace. Before that stage, however, forgettingmay already have occurred. Hence we prefer toassess the degree of associative value of items byway of a reaction time task. This involves the useof an independent pretest that to our knowledgehas not formerly been used to assess verbalmaterial in short-term memory tasks. We think,however, that this associative pretest may be amore sensitive measure of the status of items thansubjective rating of familiarity and worldlikeness,and objective frequency rating based on thecounting of occurrences in text sources, likenewspapers. Subjects participating in this pretestwill be instructed to express verbally as fast aspossible an association to the presented item, andto press a key simultaneously with the verbalresponse. An itemwise tabulation of mean reac-tion times makes possible the selection of a groupof items that are less likely to produce meaningfulassociations under time constraints, and a group ofitems that under similar conditions are more likelyto be meaningfully encoded. The response laten-cies will not distinguish types or breadths ofassociations, but probabilities with which itemswill under time constraints activate some long-term memory representation. In this way we comeup with items of low and high associative value,respectively.

More details about the selection of study itemswill be presented in the introductory section ofExperiments 1A and 1B. Both experiments dealwith serial recall of words and nonwords of highand low association value. However, Experiment1B is a replication of 1A with a new set of stimulithat are generated according to the same pro-cedure used in Experiment 1A. Experiment 2deals with serial recognition of words and non-

284 LIAN, KARLSEN, WINSVOLD

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

words, and a new task designed to study therecognition of items independent of order. Thetwo tasks, serial recognition and item identifica-tion, make equal demands on the response system.

EXPERIMENT 1A

Gathercole (1995) showed that repetition accu-racy in nonword repetition tests depended on therated wordlikeness of the nonwords. A phono-logical sound pattern constitutes a nonword in thesense that there is no lexical entry or lexeme(Lyons, 1981) corresponding to the item. Somenonwords may activate long-term representationsin the capacity of their wordlikeness, but generallygreat variation prevails among nonwords as totheir associative connectedness to long-termsemantic knowledge. Also, words may differ withrespect to the probability or speed of activation ofsome long-term memory representation. In thefollowing we shall refer to this property as asso-ciative value of study items.

The main objective of this experiment is tostudy immediate serial recall of words and non-words as a function of the associative value of thestudy items. Second, we also want to study serialrecall of words and nonwords for two rates ofpresentation. In the fast condition items will bepresented with a shorter inter-item interval thanin the slow condition. Baddeley and Lewis (1984),who demonstrated a relative independence ofspan and presentation rate, argued that tracedecay in the slow presentation condition is gen-erally compensated for by a rehearsal processbetween presented items. They also argued,however, that meaningful materials will benefitmore from a slow presentation rate, as more timepermits an activation of supporting associations.Brown and Hulme’s (1995) multicomponentmodel, which predicts item length effects withouta rehearsal mechanism, argues for a trace decaysystem that is relatively insensitive to presentationrate for both words and nonwords.

At first, however, we shall present a pretest thatwas run to assess the associative value of candi-date words and nonwords and to select the pool ofitems to be used in the present experiment. Theaim of this study is to create eight categories oflists corresponding to the factorial combinationsof Lexicality (2) by Associative value (2) byPhonological similarity (2). The levels of the for-mer two factors will include different items, butwe intend to make use of the same items to form

phonologically similar and distinct lists. However,a full overlap of items in these categories cannotbe warranted, as the distinct group will includemore vowels than those selected for the similargroup (e.g. a and e). The categories of lists will becreated in such a way that the number of repeti-tions in each condition will be the same acrosssubjects. As memory span has been shown to begreater for words than nonwords, more wordsthan nonwords will be needed.

Reaction time assessment of theassociative value of study items

The word and nonword stimuli were selected froma pool of 112 one-syllable words and 79 one-syllable nonwords. The words were high-frequency words in the Norwegian languagecharacterised by an approximately equal length ofpronunciation. They all included one vowelbetween a consonant or consonant cluster in thebeginning and the end of the word (i.e. Blest,Rull). The words were divided into two groups. Inthe first group of 56 words the eight vowels in theNorwegian alphabet (excluding œ) were aboutequally represented. Hence, these words formed agroup of phonologically distinct items. In thesecond group 28 words included the vowel a, and28 included the vowel e., and thus each of thesehalves formed a group of phonologically similaritems. The nonwords constituted only consonant-vowel-consonant (CVC) combinations, and theywere always pronounced with a short vowel; 39 ofthem included all vowels used in the words aboutequally often. This half formed the group ofphonologically distinct items. As to the rest of thenonwords, 20 included the vowel a and 20 thevowel e, i.e., two groups of phonologically similarnonwords.

Every word and nonword item was read aloudin a female voice to a computer that recorded anddigitised the items. All items in a randomised andintermixed list of words and nonwords wereplayed back to a subject, who was told to press thespace bar on a computer once he/she could comeup with an associated word or statement to theitem presented, or a word that he/she thought theitem sounded like. Simultaneously with the keypress, the subject was required to say aloud his/herassociated word/statement. It was emphasised thata mere sound-pattern reproduction of the audi-tory stimulus would not be accepted. Otherwise, aliberal practice with respect to the acceptance of

EFFECTS OF PHONOLOGICAL SIMILARITY 285

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

associative responses was followed. Key pressreaction times (RT) were recorded as indices ofassociative value of the presented items. A total of24 undergraduate students served as subjects inthe pretest.

In an itemwise tabulation of the data, the meanand standard deviation of RTs to phonologicallydistinct words were 2179 ms and 388 ms respec-tively, and for the phonologically similar wordsthe mean and standard deviation were, with the avowel, 2321 ms and 371 ms, and with the e vowel,2204 ms and 377 ms, respectively. The means ofthe three word groups did not differ significantlyfrom each other. The mean and standard devia-tion of RTs for distinct nonwords were 2846 msand 421 ms, while mean and standard deviationfor phonologically similar nonwords with the avowel were 2625 ms and 264 ms, and with the evowel, 2796 ms and 472 ms, respectively. Themeans of the three groups of nonwords did notdiffer significantly from each other, whereas themean (2216 ms) of all three groups of words dif-fered significantly from the mean (2778 ms) of allthree groups of nonwords (t = 9.70, df = 189, p <.001).

In the itemwise tabulation of RTs we definedthe mean RT as an inverse measure of Associativevalue, i.e., items with low mean RTs were con-sidered high on associative value and vice versafor items with high mean RTs. The mean/SD ratiowas taken as a measure of agreement across sub-jects on the item. The median RT in each of theword and nonword groups was used to distinguishitems of low and high associative value in thegroup, and thus we created eight groups of itemsaltogether. From each of the eight item groups weselected a few items to be used in the memoryspan experiment. We took care to include items of

high agreement ratios and to keep overlappingRTs between groups of different associative valueat a minimum. In this way we decided to use 12items in the low associative value group and 12items in the high associative value group for thephonologically distinct words. Likewise, from thephonologically similar words we selected 8 itemswith the a vowel and 8 items with the e vowel ineach of the low and high associative groups. (Thesimilar group was made larger due to the repre-sentation of two vowels.) The number of itemsselected for the phonologically similar nonwordswas 12 (6 with an a vowel and 6 with an e vowel) ineach of the two meaningfulness groups, and foreach of the two groups of phonologically distinctnonwords we selected 10 items. (We selectedmore word than nonword items because wordspans are expected to be higher than nonwordspans.)

Distinct and similar word items within each ofthe low and high associative value groups did notdiffer significantly from each other with respect tomean RT, nor did distinct and similar nonworditems. Thus, for instance, for words of low asso-ciative value, the three categories (similar with avowel, similar with e vowel and distinct) did notdiffer significantly from each other. However,items in low associative value groups always dif-fered significantly from the corresponding word ornonword items in the high associative valuegroups.

Table 1 shows the statistical descriptives of theRT data and mean presentation time of the eightgroups of items used in the experiment. Thephonologically similar words and phonologicallysimilar nonwords each contained one half of a-vowel items and one half of e-vowel items. Aspointed out, the difference in the set size for words

TABLE 1

Statistical descriptives of words and nonwords used in Experiment 1A

Words NonwordsSimilar Distinct Similar Distinct

Low High Low High Low High Low High

Number 16 16 12 12 12 12 10 10Mean 2372 1902 2394 1782 3493 2625 3436 2607Agreement 2.47 3.08 2.65 3.58 1.70 2.16 1.68 2.19Minimum 2143 1587 2147 1587 2759 2439 3014 2374Maximum 2601 2245 2680 1971 5277 2874 3900 2897Pres. time 859 799 855 788 707 732 727 678

Mean, minimum, and maximum refer to reaction time in milliseconds. Pres. time = presentation time in milli-seconds. Similar, distinct = phonological similarity. High, low = associative value.

286 LIAN, KARLSEN, WINSVOLD

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

and nonwords is due to an expected difference ofspan between the two groups’ items.

To summarise, the complete set of itemsselected for the present experiment can be cate-gorised as words and nonwords that give rise tothe factor of Lexicality with two levels. However,Lexicality is not fully independent from the factorof Associative value. The selected words have allhigher RTs compared to nonwords. On the otherhand, words and nonwords may differ in a waythat is not revealed by the present RT data, andthis possibility warrants the use of Associativevalue and Lexicality as separate factors, each withtwo levels. Although the two may be reduced toone factor of Meaningfulness with four levels, dataanalysis will primarily be undertaken to test theeffect of both factors separately. As previouslymentioned, we shall use the term Associativevalue for Meaningfulness, which we think will bemore consistent with the present operationalisa-tion of the term.

Method

Subjects. A total of 32 undergraduatestudents, 26 females and 14 males, from the Uni-versity of Oslo served as paid subjects in theexperiment. All were native speakers of Nor-wegian in the age range 20–30 years. The subjectssigned an informed consent.

Design. The experiment was run according toa repeated measures design with the factors ofPresentation rate (2) £ Lexicality (2) £ Phono-logical similarity (2) £ Associative value (2).

Materials and procedure. The word and non-word groups shown in Table 1 were used to con-struct lists for the serial recall tasks. In thephonologically similar conditions we alternatedbetween lists sharing the a vowel and lists sharingthe e vowel, and due to the representation of twovowels these categories have two more itemscompared to the distinct categories in Table 1.However, phonologically distinct lists werecreated by using some items from the similargroup within the same level of Lexicality andAssociative value, i.e., a procedure that elimi-nated differences of set size between groups ofphonologically similar and distinct categories, andwhich warranted a partial overlap of items in thetwo conditions. Before testing, subjects wereasked to listen to all words and nonwords to be

used in the experiment. They were told to repeateach of the words and each of the nonwords tocheck their audibility, and to ascertain the sub-ject’s ability to articulate each item correctly. Allsubjects who signed up for the experiment andwho took part in the test for audibility of itemsfulfilled all serial recall tasks.

Word and nonword lists of varying lengths weregenerated randomly without replacement fromeach of the eight pools of items (Table 1). For eachof the word conditions there were generated fourlists of three items, and six lists of each of thesucceeding list lengths, to a maximum list length ofeight words. Correspondingly, for nonwords fourlists of two items, and six lists of each of the listlengths from three to six items were generated.For practical reasons, no lists of the same lengthwithin the same category started with identicalitems.

In the experiment the presentation of lists wasblocked with respect to the eight groups. How-ever, the presentation of phonologically similarlists was made possible by randomly alternatingbetween a vowel and e vowel lists. Spanmeasurements started by presenting subjects withtwo lists, randomly selected from the set of four, atthe lowest sequence length, and with four lists,randomly selected at each of the other list lengths.Testing was discontinued when subjects madeerrors at all four lists of a certain length. Subjectswere credited with a score corresponding to thelist length tested when they recalled all lists at thatlength and a score of .25 for each subsequent listrecalled correctly.

The subjects were told to recall the presentedlist of items by saying each item aloud in the sameorder, and they were told to say ‘‘pass’’ for an itemthey could not remember. A response was scoredas correct only when all the sounds/speech seg-ments of the item were properly articulated, i.e., aconservative scoring regime was maintainedthroughout the experiment.

The experiment was run in two sessions, oncefor each of two rates of presentation. In one ses-sion items were presented with an interval of 300ms between the offset of one item and the onset ofanother (the fast condition) and in the othersession items were presented with an interval of1000 ms between items (the slow condition). Theorder of the two sessions was balanced acrosssubjects, and the break between sessions was aminimum of 1 hour, but varied from 1–4 hours formost subjects. The subjects were told they wouldhear a list of words or nonwords, that these

EFFECTS OF PHONOLOGICAL SIMILARITY 287

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

categories of items were not mixed in a list, andthat all items were selected from the series ofwords and nonwords presented to check for theiraudibility before testing. They were then told tolisten carefully to be able to repeat them back inthe same order with a clear and well articulatedvoice.

The entire testing session was audiotaped andreplayed later to moderate the online scoring.

Results and discussion

No significant main effect of Presentation rate onmemory span was observed. Nor did Presentationrate interact significantly with any of the otherindependent variables. We shall therefore present

mean span measures by collapsing scores for thefast and slow presentation rates. Figure 1 showsmean span measure and 95% confidence intervalfor each of the eight experimental conditions.Standard error of means varied between .07 and.11 for the different conditions. A significant maineffect of Lexicality, F (1, 31) = 221.35, MSE = .51,p < .001, supports Hulme, Roodenrys, Brown, andMercer’s (1995) finding that memory span forwords is substantially better than memory span fornonwords. There is also a main effect of Phono-logical similarity, F (1, 31) = 159.74, MSE = .19, p< .001, which conforms to a number of otherreports (Baddeley, 1966; Conrad, 1964; Longoni etal., 1993), and there is a main effect of Associativevalue, F (1, 31) = 69.82, MSE = .21, p < .001, whichis a new finding.

Figure 1. Mean short-term memory span and 95% confidence interval for each of the eight experimental conditions for phono-logically similar and distinct words and nonwords with low and high associative value in Experiment 1A.

288 LIAN, KARLSEN, WINSVOLD

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

Figure 1 also shows that Phonological simi-larity affects the word and nonword span differ-ently as documented by a significant interactionbetween Phonological similarity and Lexicality,F (1, 31) = 19.73, MSE = .34, p < .001. PSE isclearly present in the recall of nonwords withhigh associative value, but on the contrary therecall of nonwords with low associative valuebenefited from phonological similarity of thepresented items. This finding is reflected by thesignificant interaction between Phonologicalsimilarity and Associative value, F (1, 31) =21.32, MSE = .23, p < .001. Also, the three-wayinteraction between Lexicality, Phonologicalsimilarity, and Associative value was significant,F (1, 31) = 52.33, MSE = .25, p < .001, meaningthat sensitivity to phonological similarity isaffected by the associative value of nonwords,not words.

The recall data of the nonwords with lowassociative value shows a reversed effect ofPhonological similarity. Thus mean span forphonologically similar nonwords is 3.35 and fordistinct nonwords in this category 3.09, i.e., a dif-ference that is significant on a t-test of pairedsamples (t = 3.40, df = 31, p = .002). The reversedeffect of Phonological similarity by low associativenonwords is surprising. We cannot come up with aconsistent explanation of this finding, unless it canbe shown that phonologically similar lists of non-words but not words contain less information thanphonologically distinct lists in presemantic pro-cessing. In any case, when associative value istaken into account, we can conclude that wordsand nonwords are processed differently in short-term memory.

Effect of repeating items across sessions. Be-cause no effect of Presentation rate has beendemonstrated, our data do not contradict Brownand Hulme’s (1995) model. The two presentationrates were tested in separate sessions, and there-fore we are in a position to test the effect ofrepetition of items. In the experiment someproactive interference may be expected due tothe fact that the items that are presented acrosstrials are drawn from an extremely restricted set.Cross-trial confusions are more likely to occurwhen items are repeated, and such confusionsmay serve to increase PSE. As our subjects weretested twice, once for each of the two presenta-tion rates, we should find more cross-trial confu-sions in the second session. Table 2 shows PSEin the four item categories in the first and

second session of the experiment. The effect sizedid not differ significantly between sessions forany of the item categories. Yet it should beemphasised that PSE changes in opposite direc-tions for words and nonwords with high associa-tive value on the one side and nonwords withlow associative value on the other. In the lastsession, PSE becomes more negative for non-words with low associative value and more posi-tive for the other item categories.

Summary of results. The main finding inExperiment 1A has to do with PSE that occurs bywords and nonwords with high associative valueand not by nonwords of low associative value. Infact, the immediate serial recall of novel andmeaningless nonwords shows a reversed PSE, inthe sense that nonwords that are phonologicallysimilar have a slight recall advantage compared tononwords that are phonologically distinct. Thisshows that verbal items that have long-termmemory representations, either as words or non-words with high associative value, are processeddifferently from nonwords without such repre-sentations. Furthermore, our main finding under-mines the generality of PSE, and hence it isworthwhile to explore the critical conditions thatconstrain the operation of a phonological simi-larity factor. At first, however, we shall present areplication of the present experiment with othernonword items categorised with respect to asso-ciative value.

EXPERIMENT 1B

The validity of our findings for nonwords inExperiment 1A will be tested with an indepen-dent set of stimuli that is generated by the same

TABLE 2

Effects of phonological similarity, Experiment 1A

Effect of phonological similarityItemcategory

Associativevalue

Firstsession

Secondsession

Nonwords Low 7.13 7.38Nonwords High .76 .78Words Low .80 .88Words High .56 .62

Effects of phonological similarity (span of phonologicallydistinct–span of phonologically similar items) for each of fouritem categories in the first and second sessions of Experiment1A.

EFFECTS OF PHONOLOGICAL SIMILARITY 289

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

assessment procedure. In the first experimentphonologically similar lists were created byselecting items that shared a vowel, either a or e.This time we shall enhance the phonologicalsimilarity of items in a list by selecting CVC syl-lables that share a vowel and a final consonantsound. Thus tev kev pev will constitute a phono-logically similar list, whereas items in phonologi-cally distinct lists have different vowel and finalconsonant sounds, for example, kev dob tiv. IfPSE is due to a failure of discrimination inencoding, we have provided more optimal condi-tions for demonstration of this effect by adding arhyme component to the phonologically similarlists.

Two inclusion criteria were used for the selec-tion of CVC syllables. (1) They should have nosingle form occurrences in The Oslo corpus oftagged Norwegian texts (2000), which includes adatabase of 18.5 million words. (2) They shouldnot be included in the pool of nonwords used inExperiment 1A. To follow these criteria as closelyas possible, we decided to use the consonants b, d,g, k, p, r, t as the first consonant in the syllable.These consonants were then combined with thefollowing vowels: a, e, i, o, u, ø, aÊ . To reduce thelikelihood of creating single syllables that hadsingle form occurrences in The Oslo corpus wedecided to use b and v as the final consonants.From the 7 £ 7 £ 2 CVC combinations weexcluded 9 that also constituted familiar words inthe Norwegian language when spoken with a shortvowel. As all CVC were spoken with a shortvowel, we checked each of them for occurrences inThe Oslo corpus by writing them with a double vor b, i.e. tevv, revv, pabb, gabb. (When checkedwith only one final consonant we found moreoccurrences of these syllables due to the assump-tion of a long vowel pronunciation.) Of theremaining 89 CVC syllables 87 had zero occur-rences in The Oslo corpus when items with adouble consonant ending were checked, thisspelling being closer to actual pronunciation of theCVC syllables. Of the remaining two items, kub,had four occurrences, and dub had one occur-rence, which are extremely low frequencies.Interestingly, they both became nonwords of highassociative value.

The 89 CVC combinations were all differentfrom the one-syllable nonwords used in Experi-ment 1A except for three items, keb, dav, kib. Tomake possible the creation of phonologicallysimilar lists of five and six items these wereincluded in the pool of candidate items.

Reaction time assessment of theassociative value of study items

The 89 nonwords were spoken by a male voice,audiotaped, and digitised for presentation by acomputer. A total of 20 students from the Uni-versity of Oslo (12 females and 8 males with amean age of 24 years) participated in a reactiontime study designed to assess the degree of asso-ciative value for each item in the pool. Reactiontimes for a spoken word or phrase as an associa-tion to the auditory presentation of items weretabulated itemwise; items above the medianreaction time were considered as nonwords of lowassociative value, and those below the median asnonwords of high associative value. By excludingsix items from above and six items from below themedian that had the lowest agreement scores, wedefined two sets of 38 nonwords to be used in theexperiment. Mean reaction time of the 38 non-words from above the median was 4762 ms, andhence these formed the items with low associativevalue. Mean reaction time of the 38 nonwordsfrom below the median was 2880 ms, and hence,these formed the items with high associativevalue.

Method

Subjects. A total of 22 other students from theUniversity of Oslo, 12 females and 10 males,served as participants in the study. Mean age was26 years, range 19–31 years. All were nativespeakers of Norwegian, and none of them had anyknown hearing or language disability.

Design. The experiment was run according toa simple 2 by 2 design for repeated measures, i.e.nonword span as a function of Phonologicalsimilarity (2) by Associative value (2).

Materials and procedure. The 38 nonwords oflow associative value were organised into lists ofphonologically similar nonwords with the lengthsof two, three, four, five, and six items. Four listswere created for each of these list lengths. Thesame nonwords were then rearranged into lists ofphonologically distinct nonwords, four lists ateach of the five list lengths. Similarly, the 38nonwords of high associative value were organisedinto the same number of phonologically similarand distinct lists at each of the five list lengths.Thereby we created four conditions that were

290 LIAN, KARLSEN, WINSVOLD

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

presented blocked to the subject. However thefour types of lists, phonologically similar items oflow and high associative value and phonologicallydistinct items with low and high associative value,were presented in a random order for each sub-ject. The subjects were told that lists of nonwords,which might be more or less meaningless, were tobe presented for immediate serial recall. Testingstarted with the shortest lists, four lists at each listlength, and testing was discontinued when thesubject made errors on each of the four lists of agiven length. Memory span was measuredaccording to the maximum length at which thesubject recalled all lists correctly, and above thislevel we added a score of .25 for each list correctlyrecalled. The same strict scoring practice as inExperiment 1A was maintained.

Results and discussion

Figure 2 shows the mean scores together with 95%confidence intervals for the four conditions.Standard error of mean varied between .08 and .12for the four conditions. As in Experiment 1A,nonwords of low associative value show a negativePSE, but the similar—distinct difference does notreach significance (t = 2.01, df = 21, p = .057). Thisdiscrepancy between tests of significance for lowassociative nonwords in the two experiments maybe due partly to fewer subjects in Experiment 1B,partly to a difference of effect size in the twoexperiments. The mean span difference betweensimilar and distinct items may be expressed interms of a z score for the whole set of low asso-

Figure 2. Mean short-term memory span and 95% confidence interval for phonologically similar (rhyming) and phonologicallydistinct nonwords with low and high associative value in Experiment 1B.

EFFECTS OF PHONOLOGICAL SIMILARITY 291

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

ciative nonwords. In Experiment 1A this differ-ence yields a z of 6.44, and in Experiment 1B thisdifference yields a z of 5.06, showing that theeffect size is somewhat stronger in the formerexperiment. Phonologically distinct nonwords ofhigh associative value are significantly betterrecalled than phonologically similar nonwords ofhigh associative value (t = 2.52, df = 20, p = .02),i.e., an effect that agrees with the one found inExperiment 1A.

As the effects of Phonological similarity areopposite for nonwords at the two levels of Asso-ciative value, no main effect of this variable isdemonstrated in the ANOVA for repeatedmeasures. A main effect of Associative value, F (1,20) = 7.97, MSE = .17, p = .011 validates the pro-cedure used to categorise the study items withrespect to their connectedness to long-termmemory representations. Nonwords of high asso-ciative value are more like words in a serial recalltask, and although the level of performance is verylow in the present experiment, the main effect ofAssociative value is comparable to the lexicalityeffect reported by Hulme et al. (1995) andGathercole et al. (2001).

Finally, the variance analysis demonstrates asignificant effect of interaction between Phono-logical similarity and Associative value, F (1, 20) =25.21, MSE = .03, p < .001. This effect supports ourfindings in Experiment 1A and shows that serialrecall sensitivity to phonological similarity fornonwords depends on the ease with which theseitems can activate long-term memory representa-tions by the subjects. In the present experiment arhyme component increased the similaritybetween items in similar lists, and no PSE is foundfor the low associative nonwords. However, therhyme component means that the final consonantof nonwords was either v or b, and thereby wereduced the overall phonological variance in thepool and made the test a very difficult one.

The serial recall task in Experiments 1A and 1Bdepended on the retention of both items andorder. Our experiments cannot tell which of thesecomponents, the memory of items or the memoryof order, is associated with PSE for words andnonwords with high associative value. However,there is a considerable empirical literature (Con-rad, 1965; Drewnowski, 1980; Ellis, 1980; Healy,1974; Murdock & vom Saal, 1967; Wickelgren,1965) that supports the claim that PSE turns up intasks that require memory of order. Burgess andHitch (1992, 1999) and Page and Norris (1998)have reviewed the literature on computational

models of short-term memory designed to simu-late the relationship between memory of orderand PSE.

In view of the extended empirical literature inthe field (Conrad, 1965; Drewnowski, 1980; Ellis,1980; Healy, 1974; Murdock & vom Saal, 1967;Wickelgren, 1965) we assume that PSEs of wordsand nonwords of high associative value in serialrecall depend on the processing of order ratherthan items. If this assumption is correct, perfor-mance on a free recall task should be insensitive tothe phonological similarity of items. We thereforeran a pilot experiment of free recall of words, i.e.words that in Experiment 1A turned out to besensitive to this factor. A set of 16 one-syllablewords, 8 phonologically similar (sharing the evowel), and 8 phonologically distinct words wasselected for the experiment, and random sequen-ces of the similar and distinct items were audito-rily presented to subjects with the instruction torecall, in any order, as many of them as possible.Also, the 40 participating subjects were randomlyassigned one of two groups. The subjects of groupA were tested without any previous exposure tothe test items, whereas the subjects of group Blistened to all items spoken by a female voice withan inter-item pause of 1 second. This pretest pre-sentation of the study items was made twice, eachtime in a randomised order.

The results showed a slight PSE in group A butnot in group B. The effect in group A was non-significant. This shows that memory performanceis unaffected by the phonological similarity factor,independent of any pre-exposure to the studyitems. Yet we need more evidence to show (1) thatPSEs are restricted to tasks requiring order and donot occur in tasks that make a similar demand onthe response system but require memory of itemsindependent of order. Furthermore, we want todemonstrate (2) that the relationship betweenPSE and memory of order only applies to wordsand nonwords with high associative value and notto meaningless nonwords of low associative value.These will be the objectives of the next experi-ment.

EXPERIMENT 2

To study whether the association betweenphonological memory and vocabulary knowledgedepends on speech output constraints or someprior encoding or storage component Gathercoleet al. (1999) introduced the serial nonword

292 LIAN, KARLSEN, WINSVOLD

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

recognition task. Two lists of nonwords are audi-torily presented to the subject. The lists containthe same items, but are either identical (e.g. ‘‘sev,rof, dab’’ . . . ‘‘sev, rof, dab’’) or different withrespect to order (e.g. ‘‘sev, rof, dab’’ . . . ‘‘sev, dab,rof’’). The two lists of a trial may be composed ofwords or nonwords, in either case the subject isgiven a two-choice recognition task. Moreover,the lists may be composed of phonologicallysimilar or distinct items. The main point to bestressed is that the lists to be compared are eitheridentical or different with respect to order, butthey always contain the same words/nonwords.

The serial recognition paradigm makes mini-mal demands on speech output abilities, andtherefore it has been adopted in studies of short-term memory in individuals with language andspeech pathologies (Campbell & Butterworth,1985; Martin & Breedin, 1992; Shallice & War-rington, 1977). Also, serial recognition perfor-mance is strongly correlated with vocabularyknowledge and capacity for immediate serialrecall (Gathercole & Pickering, 1999; Gathercole,et al., 1999).

The serial word/nonword recognition task,which requires the retention of order, must becontrasted with another task that requires theretention of specific items. This time the subjectwill be presented with two lists of items whichalways differ in order, but are composed either ofidentical items (e.g. ‘‘teb, lef, ker’’ . . . ‘‘lef, ker,teb’’) or items that are identical except for one(e.g. ‘‘teb, lef, ker’’ . . . ‘‘lef, sev, teb’’). We shallrefer to this task as the item identification task:The subject is given a two-choice recognition taskaccording to which he/she decides whether thetwo auditorily presented lists contained exactlythe same items or if they were identical except forone item. Also in this task the items in a list maybe either phonologically similar or distinct. In thenegative trials where the lists do not containexactly the same items, the one new item may bephonologically similar (contain the same vowel)or distinct compared to the one that is replaced. Inthis way, the item identification task will includethree kinds of trials: (1) Trials with phonologicallysimilar items in the two sequences, as in theexamples just given. The new item in negativetrials always includes the same vowel as the otheritems in the list. (2) Trials with phonologicallydistinct items in the two lists, and here too nega-tive trials include a new item with the same vowelas the one in the replaced item (e.g. ‘‘koff, rav,sik’’ . . . ‘‘koff, sik, tad’’). (3) Trials with phono-

logically distinct items in the two lists; negativetrials include a new item with a vowel that differsfrom the one in the replaced item (e.g. ‘‘bev, sor,fab’’ . . . ‘‘sor, bev, fud’’). In brief we shall refer tothe three types of trials as (1) ‘‘similar’’, (2) ‘‘dis-tinct, same vowel’’, and (3) ‘‘distinct, differentvowel’’.

Contemporary models of short-term memory(Baddeley, 1986; Burgess & Hitch, 1992; Nairne,1990) which relate PSE to the confusability ofphonologically similar items will predict lowerscores on the ‘‘similar’’ trials in the item identifi-cation task compared to the ‘‘distinct, samevowel’’ and the ‘‘distinct, different vowel’’ trials. Itmay also be argued that confusability of items mayinterfere with the retention of order, and thusaccording to the contemporary models a PSE mayalso be predicted in the serial recognition task. Onthe other hand, if the present view that this effectis associated with the retention of order and notthe retention of items is correct, we will predict aPSE in the serial recognition task and no sucheffect in the item identification task.

Besides the problem of an interpretation of thePSE, we shall also deal with the problem ofwhether words and nonwords are processed dif-ferently by the phonological loop. Although thereare capacity differences for the processing of thetwo types of items, there may be no qualitativedifferences in the short-term memory of wordsand nonwords. In the latter case, any predictionswith respect to PSE will apply equally to wordsand nonwords. On the other hand, if there arequalitative differences it is likely that conditionsthat favour PSE by one type of items do not do sofor the other type of items. The results of the twopreceding experiments indicate that this effectoccurs for words having a long-term memoryrepresentation and not at all for nonwords that donot have a similar representation.

Method

Subjects. A total of 31 students of psychology,17 females and 14 males, from the University ofOslo served as subjects in the experiment. Allwere native speakers of Norwegian and none ofthem had any documented hearing or languagedisabilities.

Materials and procedure. The 22 nonwords(12 phonologically similar and 10 distinct) withlow associative value and the 28 words (16

EFFECTS OF PHONOLOGICAL SIMILARITY 293

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

phonologically similar and 12 distinct) with highassociative value were used as test items in thepresent experiment. Several schemes of test listswere prepared for each of the two tasks, the serialrecognition task and the item identification task.For example, eight pairs of lists with phonologi-cally similar words were presented at each of fivelist lengths, beginning with four words in a list andending with eight. The eight pairs of lists at eachlist length included four identical and four differ-ent list pairs. As the computer selected at randomsix pairs for presentation at each list length, thenumber of identical and different pairs did notalways match within a block but was distributed50–50 across conditions and subjects. For nonwordsequences pairs were first presented at list lengththree and ending with list length seven. In additionto the Task factor (serial recognition and itemidentification) the experiment included the factorof Lexicality (words and nonwords) and thePhonological similarity factor (similar and distinctitems in the serial recognition task, similar andtwo types of distinct pairs in the item identifica-tion task). As in the examples described earlier,we presented six pairs of lists at each of five listlengths for each of the eight plus two factorialcombinations.

Although list pairs in all conditions were pre-sented in ascending series, we could not find areliable criterion of span that was applicable to allsubjects. To obtain a span measure for each sub-ject we would have had to extend testing abovethe maximum list lengths. Instead we decided tomeasure the subjects’ performances in the rangeof list lengths presented. At the lowest list length,i.e., three and four for nonwords and wordsrespectively, errors were rare, and at the highestlist lengths most subjects scored close to chance.With only six lists presented at each list length,and with a two-choice recognition task, anelement of chance must be taken into considera-tion. We shall therefore record the total numberof correct responses over the range of list lengthsfor each of the factorial combinations included inthe experiment. Yet it is important to demonstratea main effect of List length, which is thereforeincluded as a factor in the design. However, inANOVA this factor is given four levels corre-sponding to the four list lengths shared by theword and nonword items.

All subjects served in both the serial recogni-tion task and the item identification task. Theexperiment was therefore run according to adesign for repeated measures with the factors of

Task (2) £ Lexicality (2) £ Phonological similar-ity (2) £ List length (4). In defining the Phono-logical similarity factor with two levels we shallrun the analysis twice, first by using the distinctcondition in the item identification task with thesame vowel in the replaced item in negative trials,and second with a different vowel in the replaceditem.

Results and discussion

To compare serial recognition and item identifi-cation scores for words and nonwords, we havesummed the scores over the four list lengthsshared by the two categories of items. Maximumscore when the number of correct responses issummed over these lengths is 24. Mean summedscore (M) and standard deviation (SD) are listedin Table 3 for each of four conditions in the serialrecognition task and for each of six conditions inthe item identification task.

Conditions where both lists consist of phono-logically similar items are listed as ‘‘similar’’ andshould be compared to conditions where both listsconsist of phonologically distinct items, listed as‘‘distinct’’. The PSE with higher mean scores for‘‘distinct’’ occurs in the serial recognition task forwords (‘‘similar’’ = 17.25 vs ‘‘distinct’’ = 19.77) andin the item identification task for words when‘‘similar’’ is compared to ‘‘distinct’’ with differentvowel replacement in the negative trials (‘‘simi-lar’’ = 17.96 vs ‘‘distinct’’ = 18.68). Only the for-mer difference turns out to be significant on a t-test for paired samples (t = 3.04, df = 30, p = .005).

TABLE 3

Mean scores, Experiment 2

Words NonwordsM SD M SD

Serial recognitionSimilar 17.25 2.59 17.71 2.37Distinct 19.77 2.01 17.65 2.98

Item identificationSimilar 17.97 2.50 16.42 3.01Distinct

. negative: same vowel 17.29 2.55 16.13 2.60

. negative: different vowel 18.68 2.91 15.87 2.84

Mean scores summed over the four list lengths shared bywords and nonwords in the four conditions of the serialrecognition task and the six conditions of the item identifica-tion task. M = mean. SD = standard deviation.

294 LIAN, KARLSEN, WINSVOLD

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

The latter difference is far from significant (t = .79,df = 30, p = .439).

The comparison of means shows that PSEoccurs only in the serial recognition task thatrequires the retention of order independent ofitems. Moreover, this effect is demonstrated forwords and not nonwords, and in this respect thedata agree with the results of Experiment 1A.Notice that the immediate serial recall task in

Experiments 1A and 1B and the serial recognitiontask in Experiment 2 both require the retention oforder.

Figure 3 shows the mean scores by List lengthin the two tasks, including list lengths 3 and 8 thatare not shared by the two categories of items.Graphs are plotted separately for phonologicallysimilar and distinct nonwords (a and b) and words(c and d). Results from the item identification task

Figure 3. Mean number of lists with similar and distinct vowels correctly recognised in the item identification task (a and c) and theserial recognition task (b and d) for nonwords (a and b) and words (c and d) at each of five list lengths in Experiment 2.

EFFECTS OF PHONOLOGICAL SIMILARITY 295

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

with the two types of study items are shown in (a)and (c), and the results from the serial recognitiontask are shown in (b) and (d). The analysis ofvariance, however, is based on the summed scoresacross the four list lengths shared by the twocategories of items. We shall start by disregardingthe ‘‘distinct, different vowel’’ condition in theitem identification task. We then find a strongmain effect of List length, F (3, 90) = 68.09, MSE =1.54, p < .001, which shows the increasing diffi-culty of both tasks with increasing list length. Notethat there is a main effect of Task, F (1, 30) =14.95, MSE = 1.60, p = .001, which shows that theitem identification task (mean score across con-ditions: 33.05) has been more difficult than theserial recognition task (mean score across condi-tions: 36.19). Finally, we find a main effect ofLexicality, F (1, 30) = 31.67, MSE = .70, p < .001,which shows that scores are higher for words(mean score across tasks and conditions: 18.07)than nonwords (mean score across tasks andconditions: 16.98).

There is no main effect of Phonological simi-larity. On the other hand, we find a significantinteraction between Task and Phonological simi-larity, F (1, 30) = 6.11, MSE = 1.46, p = .019, whichshows that PSE only occurs in the serial recogni-tion task. This finding supports our hypothesisthat the effect is related to the processing ofinformation about order of items and not to theretention of separate items. In comparing Figure 3b and d we also find that PSE in recognition oforder is limited to words. The order of nonwords isrecognised equally well regardless of whether thelists constitute series of phonologically similar ordistinct items. Thus, we find a significant three-way interaction effect between Task, Phonologi-cal similarity, and Lexicality, F (1, 30) = 5.71, MSE= 5.71, p = .023.

A second ANOVA for repeated measures wasundertaken when the ‘‘distinct’’ condition in theitem identification task was changed from samevowel replacement to different vowel replace-ment. This means that the second list in negativetrials included an item with a vowel that did notappear in the items of the first list. This may havecreated a pop-out effect, and the probability of thedetection of change will be high. The three maineffects (i.e. effects of List, Task, and Lexicality)remain significant in the second analysis, and thistime the analysis also demonstrates a main effectof Phonological similarity, F (1, 30) = 4.24, MSE =1.13, p = .048, which means that memory perfor-mance is better for lists of phonologically distinct

items. However, Table 3 shows that this differenceis mostly due to the similar–distinct difference forwords in the serial recognition task. But phono-logically distinct lists of words are also scoredhigher than phonologically similar lists in the itemidentification task. Subjects easily noticed the newitem with a different vowel in word but not non-word lists. This shows that the absence of a sig-nificant two-way interaction effect between Taskand Phonological similarity, F (1, 30) = 3.29, MSE= 1.07, p = .08, is due to sensitivity to vowelreplacement in the word list rather than an effectof phonological similarity in the similar con-ditions.

The last ANOVA also demonstrates a sig-nificant Lexicality by Phonological similarityinteraction, F (1, 30) = 11.00, MSE = 1.05, p = .002,which shows that PSE is restricted to words. In anycase, the summed scores for ‘‘similar’’ and ‘‘dis-tinct’’ conditions do not differ significantly in theitem identification task, which means that no PSEhas been demonstrated in this test. Moreover, wefind no evidence for this effect when the presenteditems consist of nonwords, neither in the serialrecognition task nor in the item identificationtask.

GENERAL DISCUSSION

The effect of phonological similarity (PSE) onshort-term memory for words and nonwords hasbeen tested in two tasks of serial recall, in one taskof serial recognition, and one item identificationtask. This effect has been replicated in a vastnumber of experiments; thus Nairne and Kelley(1999) characterised the effect as the benchmarkfinding in short-term memory literature. Despiteits assumed robustness, we have only demon-strated PSE in tests of serial recall and serialrecognition of order. No significant PSE isdemonstrated in an item identification task, andthe results of a pilot experiment on free recall ofwords indicate that the effect is absent when itemsdo not have to be recalled in the correct order.These data support the claim made in theempirical literature, that PSEs are generallyrestricted to tasks that require the retention oforder (Conrad, 1965; Drewnowski, 1980; Ellis1980; Healy, 1974; Murdock & vom Saal, 1967;Wickelgren, 1965).

Researchers in the field of short-term memoryhave generally proposed some form of inter-ference interpretation of PSE (Baddeley, 1968;

296 LIAN, KARLSEN, WINSVOLD

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

Brown, Hulme & Preece, 2000; Burgess & Hitch,1992, 1999; Houghton, 1990; Nairne, 1990; Page &Norris, 1998; Schweickert, Guentert, & Hers-berger, 1990). This interpretation involves a dis-advantage for the retrieval of phonologicallysimilar items, and applies equally to the short-term memory of words and nonwords. The lit-erature includes reports that indicate that this is infact the case. Thus Besner and Davelaar (1982)have demonstrated that phonological similarityaffects the retention of verbal items regardless ofthe wordlikeness of these items, and Papagno andVallar (1992) found that the phonological simi-larity factor affects the learning of novel wordsmore than familiar words. The definition andselection of nonwords may have influenced theseresults. This is why we made a reaction-time-basedassessment of the associative value of items to beused in our experiments. Moreover, we found thatthe serial recall of nonwords, which according tothis assessment had high associative value, wasaffected by the phonological similarity of items inthe list. However, the span measures with itemshaving low associative value were not equallyaffected by the phonological similarity factor. Onthe contrary, lists of phonologically similar itemsof this category were more likely to be recalledthan lists of phonologically distinct items in aserial recall task. Furthermore, we have shownthat PSE in recognition of order applies to wordsbut not nonwords having a low associative value.

The finding that PSE occurs with words andnonwords of high associative value, and not withnonwords of low associative value, shows that theeffect depends on the activation of long-termmemory mechanisms. However, we also foundthat nonwords of high associative value are moreprone to phonological similarity in serial recallthan words of high associative value. However,the difference in PSE between the high associativenonwords and the two groups of words is non-significant, indicating that semantic processes dovery little to reduce PSE, as predicted bySchweickert (1993). However, the differencebetween PSE for nonwords of high associativevalue and the negative phonological similarityeffect seen for nonwords of low associative valueis significant, indicating that the disappearance ofPSE for nonwords of low associative value is notdue to a floor effect.

In our opinion these results reflect that PSEoccurs in a fundamental lexical-phonologicallayer. This layer may also be identified as thehigher phonological space, in contrast to the

lower-level phonological network found in theinteractive model proposed by Gathercole andMartin (1996). Both words and nonwords of highassociative value easily access this fundamentallayer, where stable, lexical clusters and theirsimilar neighbours are activated. These activa-tions cannot be overruled by their respectiveconnections to unrelated and less confusablesemantic representations. If, however, the activa-tion of these clusters decays, or is already low ornon-existent, there should be less to confuse, andPSE should be reduced. This will happen forwords when there is a delay between presentationand recall (Nairne & Kelley, 1999). It will nothappen for some nonwords which do not rely onstable, semantic representations and are not sen-sitive to phonological similarity in the first case.Also, if item representations in the lexicalphonological layer are activated to a very smallextent simply because they are not accessed, thenPSE too will be very small or absent, as we see fornonwords of low associative value. Indeed, at thislevel we see a negative phonological similarityeffect. This may be due to the unusually low levelof representation relied upon for these items. At alower and pre-lexical phonological layer,phoneme or syllable segments may be representedand activated in new, unstable clusters. Hartleyand Houghton (1996) would predict PSE also atthis level, based on the activation of syllabletemplates of related phonemes. As each remem-bered item consists of several phonemes, therewill be a very heavy memory load when that levelof representation must be relied upon. Perhaps alist of phonemically similar items simply implies alower memory load than a list of phonemicallydistinct items at this level of representation.

It seems unlikely that the opposite effects ofphonological similarity for nonwords of high andlow associative value are due to different types ofcontrolled strategy. The two classes of nonwordsare highly similar, the subjects do not know whatclass of nonwords they will be hearing next, andthere are clear time restrictions imposed by thesteady presentation rate. This indicates that asystematic adoption of different strategies for thetwo classes of nonwords will be extremely diffi-cult.

During the redintegration process (Brown &Hulme, 1995) or the similar matching process(Nairne, 1990), clusters of segments at the lower-level phonological layer are reconstructed by theactivated long-term units of the higher-levelphonological layer. If there are few long-term

EFFECTS OF PHONOLOGICAL SIMILARITY 297

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

lexical-phonological units activated, memory spanwill decrease, and there will be less PSE.

A somewhat different interpretation of ourfindings in Experiments 1A and 1B is related tothe redintegration process (Brown & Hulme,1995) or the similar matching process (Nairne,1990) described briefly in our introduction.Instead of focusing on different layers of itemrepresentations, one may look at the connectionsbetween the different representational layers. Inthis case PSE is due to inhibition of certain con-nections between different layers rather thaninterference between activated items at a certainlayer. The excitation of a certain connectionbetween a lexical-phonological layer and asemantic layer due to the presentation of afamiliar verbal item may lead to the inhibition ofconnections from related neighbours of that itemat the lexical-phonological layer to their respec-tive and unrelated semantic representations.When neighbours at the lexical-phonological layerare presented together, that will lead to the sameconnections being both excited and inhibited. Thenet excitation will thereby be lower for each itemthan for items that are not lexical-phonologicalneighbours. Such a system would be tuned forvariance in verbal material. In this case phonolo-gically distinct sounds have an advantage com-pared to phonologically similar sounds whensemantic connections are activated. Such a systemwould also secure great precision in the semanticprocessing.

REFERENCES

Baddeley, A.D. (1966). The influence of acoustic andsemantic similarity on long-term memory for wordsequences. Quarterly Journal of Experimental Psy-chology, 18, 302–309.

Baddeley, A.D. (1968). How does acoustic similarityinfluence short-term memory? Quarterly Journal ofExperimental Psychology, 20, 249–263.

Baddeley, A.D. (1986). Working memory. Oxford:Oxford University Press.

Baddeley, A.D., & Lewis, V.J. (1984). When does rapidpresentation enhance digit span? Bulletin of thePsychonomic Society, 22, 403–405.

Besner, D., & Davelaar, E. (1982). Basic processes inreading: Two phonological codes. Canadian Journalof Psychology, 36, 701–711.

Brown, G.D.A. (1997). Formal models of memory forserial order: A review. In M.A. Conway (Ed.),Cognitive models of memory (pp. 47–77). Cam-bridge, MA: MIT Press.

Brown, G.D.A., & Hulme, C. (1995). Modelling itemlength effects in memory span: No rehearsal

needed? Journal of Memory and Language, 34,594–621.

Brown, G.D.A., Hulme, C., & Preece, T. (2000).Oscillator-based memory for serial order. Psycho-logical Review, 107, 127–181.

Burgess, N., & Hitch, G.J. (1992). Toward a networkmodel of the articulatory loop. Journal of Memoryand Language, 31, 429–460.

Burgess, N., & Hitch, G.J. (1999). Memory for serialorder: A network model of the phonological loopand its timing. Psychological Review, 106, 551–581.

Campbell, R., & Butterworth, B. (1985). Phonologicaldyslexia and dysgraphia in highly literate subjects: Adevelopmental case with associated deficits ofphonemic processing and awareness. QuarterlyJournal of Experimental Psychology, 37A, 435–476.

Conrad, R. (1964). Acoustic confusions in immediatememory. British Journal of Psychology, 55, 75–84.

Conrad, R. (1965). Order error in immediate recall ofsequences. Journal of Verbal Learning, 4, 161–169.

Conrad, R., & Hull, A.J. (1964). Information, acousticconfusion and memory span. British Journal ofPsychology, 55, 429–432.

Drewnowski, A. (1980). Attributes and priorities inshort-term recall: A new model of memory span.Journal of Experimental Psychology: General, 109,208–250.

Ellis, A.W. (1980). Errors in speech and short-termmemory: The effects of phonemic similarity andsyllable position. Journal of Verbal Learning andVerbal Behavior, 19, 624–634.

Estes, W.K. (1973). Phonemic coding and rehearsal inshort-term memory for letter strings. Journal ofVerbal Learning & Verbal Behavior, 12, 360–372.

Gathercole, S.E. (1995). Is nonword repetition a test ofphonological memory or long-term knowledge? It alldepends on the nonwords. Memory & Cognition, 23,83–84.

Gathercole, S.E. (1997). Models of verbal short-termmemory. In M.A. Conway (Ed.), Cognitive models ofmemory (pp. 13–45). Cambridge, MA: MIT Press.

Gathercole, S.E., & Martin, A. (1996). Interactive pro-cesses in phonological memory. In S.E. Gathercole(Ed.), Models of short-term memory. Hove, UK:Lawrence Erlbaum Associates Ltd.

Gathercole, S.E., & Pickering, S.J. (1999). Estimatingthe capacity of phonological short-term memory.International Journal of Psychology, 34, 378–382.

Gathercole, S.E., Pickering, S.J., Hall, M., & Peaker,S.M. (2001). Dissociable lexical and phonologicalinfluences on serial recognition and serial recall. TheQuarterly Journal of Experimental Psychology, 54A,1–30.

Gathercole, S.E., Service, E., Hitch, G.J., Adams, A-M.,& Martin A.J. (1999). Phonological short-termmemory and vocabulary development. Further evi-dence on the nature of the relationship. AppliedCognitive Psychology, 13, 65–77.

Hartley, T., & Houghton, G. (1996). A linguistically-constrained model of short-term memory for non-words. Journal of Memory and Language, 35, 1–31.

Healy, A.F. (1974). Separating item from order infor-mation in short-term memory. Journal of VerbalLearning and Verbal Behavior, 13, 644–655.

298 LIAN, KARLSEN, WINSVOLD

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014

Houghton, G. (1990). The problem of serial order: Aneural network memory of sequence learning andrecall. In R. Dale, C. Mellish, & M. Zock (Eds.),Current research in natural language generation.Hove, UK: Lawrence Erlbaum Associates Ltd.

Hulme, C. (1984). Developmental differences in theeffects of acoustic similarity on memory span.Developmental Psychology, 20, 650–652.

Hulme, C., Newton, P., Cowan, N., Stuart, G., & Brown,G. (1999). Think before you speak: Pauses, memorysearch, and trace redintegration processes in verbalmemory span. Journal of Experimental Psychology:Learning, Memory and Cognition, 25, 447–463.

Hulme, C., Roodenrys, S., Brown, G.D.A., & Mercer,R. (1995). The role of long-term memory mechan-isms in memory span. British Journal of Psychology,86, 527–536.

Hulme, C., & Tordoff, V. (1989). Working memorydevelopment: The effects of speech rate, wordlength, and acoustic similarity on serial recall. Jour-nal of Experimental Child Psychology, 47, 72–87.

Longoni, A.M., Richardson, J.T.E., & Aiello, A. (1993).Articulatory rehearsal and phonological storage inworking memory. Memory & Cognition, 21, 11–22.

Lyons, J. (1981). Semantics, Vol. 1. London: CambridgeUniversity Press.

Martin, R.C., & Breedin, S.D. (1992). Dissociationsbetween speech perception and phonological short-term memory deficits. Cognitive Neuropsychology,9, 509–534.

Murdock, B.B., & vom Saal, W. (1967). Transpositionsin short-term memory. Journal of ExperimentalPsychology, 74, 137–143.

Murray, D.J. (1968). Articulation and acoustic con-fusability in short-term memory. Journal of Experi-mental Psychology, 78, 679–684.

Nairne, J.S. (1990). A feature model of immediatememory. Memory & Cognition, 18, 251–269.

Nairne, J.S., & Kelley, M.R. (1999). Reversing thephonological similarity effect. Memory & Cognition,27, 45–53.

Page, M.P.A., & Norris, D. (1998). The primacy model:A new model of immediate serial recall. Psycholo-gical Review, 105, 761–781.

Papagno, C., & Vallar, G. (1992). Phonological short-term memory and the learning of novel words: Theeffect of phonological similarity and item length. TheQuarterly Journal of Experimental Psychology, 44A,47–67.

Salame, P., & Baddeley, A.D. (1986). Phonologicalfactors in STM: Similarity and the unattendedspeech effect. Bulletin of the Psychonomic Society,24, 263–265.

Schweickert, R. (1993). A multinominal processing treemodel for degradation and redintegration inimmediate recall. Memory & Cognition, 23, 168–175.

Schweickert, R., Guentert, L., & Hersberger, L. (1990).Phonological similarity, pronunciation rate, andmemory span. Psychological Science, 1, 74–77.

Shallice, T., & Warrington, E.K. (1977). Auditory-verbal short-term memory impairment and conduc-tion aphasia. Brain and Language, 4, 479–491.

The Oslo corpus of tagged Norwegian texts. (Lastupdated June 2000). http://www.tekstlab.uio.no/norsk/bokmaal/english.html

Wickelgren, W.C. (1965). Short-term memory forphonemically similar lists. American Journal ofPsychology, 78, 567–574.

EFFECTS OF PHONOLOGICAL SIMILARITY 299

Dow

nloa

ded

by [

Cas

e W

este

rn R

eser

ve U

nive

rsity

] at

13:

08 2

4 N

ovem

ber

2014