target-noise separation in visual selective attention

Acta Psychologica 62 (1986) 161-176 North-Holland

161

TARGET-NOISE SEPARATION IN VISUAL SELECTIVE ATTENTION

Ruchama HAGENAAR * and A.H.C. van der HEIJDEN University of Leiden, The Netherlands

Accepted October 1985

Several studies have reported a decrease of interference caused by the categorical nature of noise stimuli, i.e., identity-dependent interference, with increasing physical target-noise separation. Such a result is generally regarded as evidence in favour of precategorical selection (‘beam-of- spot-light’) views of attention, Analysis of these studies, however, reveals that target-noise distance covaried with distance of the noise elements from the fixation point, that is, with retinal acuity. In this study, two experiments are reported in which identity-dependent interference in a colour-naming task (the ‘Stroop effect’) was investigated as a function of colour-noise separation. All stimulus elements were projected on positions of equal retinal acuity. No effect of target-noise separation was observed. The results are interpreted as evidence in favour of postcategorical-selection views; selective attention deals with identified information and has its function in the programming and execution of further actions like memory storage and overt responding.

General introduction

A great number of authors consider selective attention to be like a beam of spot-light (e.g., Eriksen and Hoffman 1973; Eriksen and Eriksen 1974, 1979; Kahneman and Henik 1981; Broadbent 1982; La- Berge 1983; Neumann 1980,1984a, b; Kahneman and Treisman 1984). Information within the beam is processed in detail, information falling outside the beam is not processed or receives only very gross, preattentive, processing. (In this study the term ‘processing’ is used in a rather strict sense, that is, for identification or categorization.) For evidence in favour of this view, one often refers to experiments in which apparently the severity of identity-dependent interference or facilitation, that is, interference or facilitation due to the categorical nature of a to-be-

* Mailing address: R. Hagenaar, Dept. of Psychology, Unit of Experimental Psychology, Univer- sity of Leiden, Hooigracht 15, 2312 KM Leiden, The Netherlands.

OOOl-6918/86/$3.50 0 1986, Elsevier Science Publishers B.V. (North-Holland)

162 R. Hagenaar, A.H.C. uan der Heijden / Target-noise separation

ignored object, decreases with increasing target-noise separation. Un- fortunately, however, none of these experiments provides really convincing evidence for this type of spacing effect. We first discuss and comment upon the relevant experiments.

In the paradigms used in these experiments the subject was briefly presented with one of a very small set of targets at a specified location in the visual display. The subject had to indicate vocally or manually which target was present. The location of the target was either indicated by a pointer or the target was always in the same central position of the display. The target item could appear alone, or, together with some other stimulus elements. These elements were associated either with the response on the target (compatible noise), with the other response(s) in the experiment (incompatible noise) or not associated with any response (neutral noise). The dependent variable was response latency (RT).

The relevant experiments can be classified according to the type of target stimuli employed: letters (or digits) and colour patches.

Letter-recognition tasks

In the three studies on spatial selectivity by Eriksen and colleagues to be discussed here, two sets of two letters were employed as stimulus items. The subject responded to the target with a right or left lever press, dependent upon the set which the target belonged to.

Eriksen and Hoffman (1973) used 12-letter circular arrays, composed of the four letters, around a central fixation point, and a line indicator preceding exposure at variable intervals. The results showed that response times were larger when the target lay in close proximity to incompatible letters rather than to compatible letters, and, more importantly, that there was an inverse relationship between the interference of incompatible letters and distance from the target letter. In line with Eriksen and Rohrbaugh (1970) and Eriksen and Hoffman (1972), Eriksen and Hoffman (1973) interpret the decreasing interference with increasing distance in terms of a limit to the precision of selective attention in the visual field. Another, much simpler, explanation is possible, however. The exposure duration was 1000 msec and the indicator preceded the display. Therefore, the subjects had sufficient time to make a saccadic eye movement to the target position. Subse- quent research even showed that inexperienced subjects cannot resist

R. Hagenaar, A.H.C. uan der Heijden / Target-noise separation 163

making such eye movements (see Colegate et al. 1973). When the target is fixated, also with circular arrays, letters adjacent to the target fall’on positions of higher retinal acuity than letters two or three positions removed. Accordingly, the decreasing interference can as simply be interpreted in terms of retinal acuity as in terms of a property of an attentional mechanism.

In their later research Eriksen and Eriksen (1974, 1979) used linear instead of circular arrays in a similar type of task. To prevent search, the target always appeared in the centre of the array, just above the fixation point. Again, interference from incompatible letters (and facilitation from compatible letters) was found, an effect decreasing with increasing separation. Eriksen and Eriksen essentially maintain the imperfect-attentional-field interpretation. Broadbent agrees with this interpretation and proposes as a good rule ‘( . . .) that events more than 1 degree from the target are unlikely to interfere’ (1982: 271). But the linear array data neither warrant such an interpretation nor support such a rule, for the same reason as the circular array data. With linear arrays having the target in the centre, an increase in target-noise separation results in the noise letters being projected on retinal positions with reduced retinal acuity. Therefore, the effects of spacing can be more parsimoniously explained in terms of retinal acuity and, again, the hypothesis of an imperfect attentional mechanism is not necessary. Convincing evidence for this retinal acuity interpretation was provided by Whitehouse, Somers, and Egeth (cited in Egeth (1977: 289)) and Gatti and Egeth (cited in Egeth (1977: 291)) in experiments in which larger characters were used to compensate for reduced acuity with increased target-noise distance (see Merikle and Gorewich (1979) and Eriksen and Schultz (1979) for related results).

Colour-naming tasks

In two experiments on spatial selectivity a variant of the Stroop colour-word task was employed. In both experiments, the subjects saw a centrally located colour patch; with noise words above and below it at variable distances.

Gatti and Egeth (1978) found that interference of incompatible, and facilitation of compatible, colour words decreased with increasing distance, but even so was still present at the widest distance (5 degrees).

164 R. Hagenaar, A. H. C. van der Heijden / Target-noise separation

Merikle and Gorewich (1979) extended the task by varying also the lettersize in order to compensate for reduced retinal acuity at wider distances. They essentially replicated the results of Gatti and Egeth (1978) for their largest letters, but found no interference with smaller noise letters at their largest spacing (2.5 degrees).

Gatti and Egeth (1978) and Merikle and Gorewich (1979) favour an explanation of their results and those of Eriksen and associates in terms of limitations in visual acuity for the noise letters. But, many others take the latter results as indicating the operation of an attentional mechanism with imperfect precision (see, e.g., Kahneman and Henik 1981; Neumann 1980, 1984a, b; and Kahneman and Treisman 1984). According to Neumann, for instance, the decrease in interference observed when target and distractor are moved away from one another, indicates that Stroop-like interference depends on the focusing of attention.

However, Gatti and Egeth’s (1978) and Merikle and Gorewich’s (1979) paradigms are not suitable for studying spacing effects either. Also in their experiments possible attentional effects of spacing are completely confounded with effects due to retinal acuity.

Taken together, it seems that, until now, no experiments have been reported that provide unequivocal evidence in favour of a spacing effect resulting from the operation of an attentional mechanism as a too large or imprecise spot-light. In this study we report the results of two experiments that address this issue. In both experiments we used variants of the Stroop task to assess identity-specific effects of irrelevant noise elements as a function of target-noise separation under conditions of equal retinal acuity. Given these conditions, the results will either provide evidence for precategorical-selection, beam-of-spot- light, views (when no effects of noise elements, or a decreasing identity-specific effect with increasing target-noise separation will be found), or, for postcategorical-selection views (when the effects of noise elements appear to be independent of target-noise separation).

Experiment 1

Introduction

The experiment reported here attempted to investigate the spacing variable in a selective attention task that is not subject to retinal acuity variations.

R. Hagenaar, A.H.C. uan der Heijden / Target-noise separation 165

In the experiment, we used a variant of the Stroop task, with spatially separate colours and words. In this type of task, the time needed by subjects to name the colour of the colour patch is measured. It appears that, relative to neutral words, the presence of colour words that are incompatible to the colour patch causes a delay in colour-naming time (see, e.g., Dyer 1973; Van der Heijden 1981; and Glaser and Glaser 1982). On each trial in our experiment a colour patch was presented together with either a neutral word or an incompatible colour word. Positions of equal retinal acuity were assured by positioning colours and words on an imaginary circle around the fixation point. The exposure duration was too short to permit useful eye movements. The distances between colour and word were chosen such that recognition of the noise word is unlikeiy to be impaired by lateral masking by the contour of the colour patch. Although we used latency measures and not accuracy, we relied for this upon Bouma’s (1970) rule, which says that the spatial range of interaction is about 50% of eccentricity. Because of the absence of contour interaction, we predict that in our neutral condition no difference between colour-naming times for the two spacings will be found. With regard to the incompatible word condition, three groups of predictions can be dis- tinguished depending on the theoretical position that is taken.

According to a ‘perfect-precategorical-selection’ view, in a paradigm such as that used in the present experiment ‘( . . ) the involuntary reading of a distant color word can be prevented by focusing attention on the relevant visual object’ (Kahneman and Chajczyk 1983: 498; see Neisser (1967) and Francolini and Egeth (1980) for similar views). But, if word reading is prevented, incompatible colour words are in all respects functionally equivalent to neutral words. Therefore, no main effect of conditions (neutral versus incompatible words), no main effect of spacing (remember that no spacing effect in the neutral condition is expected), and no condition by spacing interaction is predicted (see fig. la).

According to an ‘imperfect-precategorical-selection’ view (see, a.o., Eriksen and associates (Eriksen and Rohrbaugh 1970; Eriksen and Hoffman 1972, 1973; Eriksen and Eriksen 1974), Broadbent (1982) and Neumann (1980,1984a, b) for this view and closely related beam-of-spot-light views), the extent of processing which a word receives in our paradigm depends on the distance between the target colour patch and the distractor word. Accordingly, words are not excluded from processing, and a (possibly minor) effect of condition (incompatible versus neutral words) is predicted. When an incompatible colour word is close to the target, however, it will receive a high degree of processing and will, therefore, interfere more with the naming of the colour than the same word further removed from the colour patch. Therefore, a (possibly minor) effect of spacing and, more importantly, an interaction between spacing and conditions is predicted (see fig. lb).

According to ‘postcategorical-selection’ views, in our paradigm all the information is processed automatically, ‘( . . . ) whether attention is paid to it or not ( . . )’ (Deutsch 1963: 83; see, e.g., Norman (1968) Keele (1973) Shiffrin and Schneider (1977) and Van der Heijden (1981) for similar views). In postcategorical-selection views, attention has nothing to do with the processing (i.e., identification) of the information, but has its function in routing identified information and in controlling priorities (Posner 1980: 9). Because identification of all information is assumed, a main effect of conditions (neutral versus incompatible words) is predicted. Because distance is assumed to be

Rl

+---e

;nco

mpa

tible

- ne

utra

l

“Cji-r

ClW

wi

se

targ

et-n

oise

se

para

tion

(a)

RT

0 4J

I I

“W-rO

W

wid

e

targ

et-n

oise

se

para

tion

(b)

(0)

R7

tar-g

et-n

o i s

e se

para

t i o

n

Fig.

1. Pr

edict

ed

result

s in

Stro

op

tasks

wi

th

spati

ally

sepa

rate

pres

entat

ions

of tar

get

and

noise

ac

cord

ing

to thr

ee

differ

ent

theor

etica

l po

sition

s: (a)

pe

rfect-

prec

atego

rical-

selec

tion

view;

(b)

im

perfe

ct-pr

ecate

goric

al-se

lectio

n vie

w;

(c)

postc

atego

rica!-

selec

tion

view.

Se

e tex

t for

fur

ther

expla

natio

n.

R. Hugenaar, A.H.C. uan der Heijden / Target-noise separation 161

irrelevant (in both spacing conditions colour and word are separated sufficiently to make easy selection possible), neither a main effect of spacing nor a condition by spacing interaction is predicted (see fig. lc).

Method

Apparatus Stimuli were presented with a Scientific-Prototype three-channel tachistoscope

(model 320 GB) connected to an electronic timer. Subjects initiated stimulus exposure by pressing a button on the table surface. The timer started counting when a stimulus card appeared and stopped as soon as the subject spoke his response into a voice key. Response times were recorded accurate to 1 msec. The pre- and postexposure fields consisted of a blank card with a black fixation cross in the centre. The stimulus cards and the blank cards appeared at a luminance of about 50 cd/m’.

Subjects Twelve students from the University of Leiden, six male and six female, served as

paid subjects. They all had normal or corrected-to-normal visual acuity and none of them was deficient in colour vision.

Stimuli and experimental conditions Each white stimulus card contained either a red or a blue colour patch and a word

printed in black. The words used were ‘ROOD’ (red), ‘BLAUW’ (blue) and ‘SMAL (narrow). Two colour-word combinations were used:

- neutral combinations (a red or blue patch with the word ‘SMAL’); and - incompatible combinations (a red patch with the word ‘BLAUW’ or a blue patch

with the word ‘ROOD’).

The colour patch was located in one of four positions on an imaginary clock face having a diameter of 2.19 degrees. The hour positions were one, five, seven and eleven o’clock. The word was placed either two (near condition) or four (far condition) hour positions away from the colour, moving either in a clockwise or a counter-clockwise direction. Fig. 2 may clarify the stimulus construction.

In total 64 stimulus cards were prepared, representing the factorial combination of 2 colours (red and blue) X 4 colour positions (see fig. 2a) X 2 distances (see fig. 2b) X 2 word positions (clockwise or counter-clockwise moved away from the colour patch, see fig. 2b) ~2 conditions (neutral and incompatible).

Each patch had a diameter of 0.56 degree of visual angle. The word height was 0.24 degree and the word width varied from 0.92 for ‘ROOD’ (red) and ‘SMAL’ (narrow) to 1.14 degree for ‘BLAUW’ (blue). The distances between colour patches and words, measured from centre to centre, were 1.09 degree (near condition) and 1.89 degree (far condition).

168 R. Hagenaar, A.H.C. uan der Hezjden / Target-noise separation

word

ial fb)

ROOD

(CJ

Fig. 2. Construction of the stimuli in experiment 1: (a) positions used for target colours (0) and/or for distractor words (‘word’); (b) possible positions of the word (‘word’) given the location of the colour patch (0); (c) example of a stimulus card: colour top right, word right and at the largest distance.

Design The 64 stimulus cards were presented three times to each subject, each time in a

different random order. The three presentations where separated by short rest periods. RTs on correct trials only were included in the analysis.

Procedure The subjects were tested individually in a moderately illuminated room. They were

asked to name the colour of the patch as fast as they could, to ignore the word, and to try and avoid errors. They were instructed to initiate stimulus exposure any time after they clearly saw the fixation cross. Stimulus duration was 150 msec. No information was given to the subjects about their RTs or the correctness of their responses.

Prior to the beginning of the experiment proper, the subjects were familiarized with the stimuli and the task, and received 32 practice trials. Practice data were not recorded.

Results

The results that are relevant to the hypotheses outlined in the Introduction are presented in fig. 3. The data have been collapsed across colour, colour position and word position.

An analysis of variance on the mean RTs with condition (neutral or incompatible) and colour-word distance (1.09 or 1.89 degrees) as factors showed a significant effect of conditions (F(1, 11) = 7.38; p < 0.05; the mean RTs for the neutral and incompatible conditions were 496 and 512 msec, respectively). The main effect of distance (F(1, 11) = 0.65) and the interaction between conditions and distance (F(1, 11) = 0.64) were far from significant.

The error rate was very low (about 1% of the responses) and did not allow a meaningful analysis of errors.

R. Hagenaar, A.H.C. vun der Heijden / Target-noise separation 169

t . incompatible

500 Y neutral

480 1 ,

1.09O I

1.89’

Fig. 3. Mean RTs for colour-naming in the neutral and incompatible conditions as a function of target-noise separation (experiment 1).

Discussion

The outcome of the experiment is extremely clear. A comparison of fig. 1 and fig. 3 shows that our results support the postcategorical-selection view, and fail to provide any evidence for the perfect and for the imperfect-precategorical-selection views. The results of the analysis of variance support this conclusion. As predicted by the postcategorical-selection view, the main effect of conditions is significant, whereas the main effect of distance and the condition by distance interaction are far from significant. This pattern of results is not consistent with the perfect-precategorical- selection and imperfect-precategorical-selection views.

The size of the ‘Stroop effect’, that is, the difference between the latencies for the incompatible and neutral combinations, appears rather small in the present experiment (16 msec). Values reported in the literature generally range from 70 msec to 200 msec. Two issues are of special importance here. Firstly, these values were obtained with integral combinations of words and colours. Spatial separation of word and colour appreciably reduces the Stroop effect (see, e.g., Dyer 1973; and Van der Heijden 1981: exp. 2; see Van der Heijden et al. (1984) for an explanation of this reduced interference). Secondly, these values resulted from comparison with a non-word neutral condition (e.g., XXX or * * *). In the present experiment, however, an irrelevant word was used in the neutral condition. Klein (1964) showed that an irrelevant-word neutral condition takes appreciably more time than a non-word neutral condition. Hence, an appreciably smaller Stroop effect has to be expected with a word than with a non-word neutral condition. Taken together, the conditions in the present experiment are such that only a small Stroop effect has to be expected.

170 R. Hugenaar, A.H.C. uan der Heijden / Target-noise separation

Experiment 2

Introduction

The results obtained in experiment 1 c;learly support the postcategorical-selection view and fail to provide any evidence in favour of the perfect-precategorical-selection and the imperfect-precategorical-selection views. Proponents of the imperfect-precategorical-selection view might argue, however, that the experiment did not provide a fair test for their point of view. They could complain that neither the position of the target (the colour patch) nor the position of the distractor word was known in advance. Therefore, the beam of spot-light might have passed the noise word in search for the target, or, the beam might have not been sharply focused initially, that is, diffused. In both cases substantial processing of the noise word would become possible. Hence identity-specific interference would result. In Broadbent’s (1982) terms: ‘Whatever the size of the beam at any instant, everything within it obtains access to a further processing system, so that if there are stimuli inconsistent with the message conveyed by the target one, they will interfere, (. . .)’ (Broadbent 1982: 271).

What is needed, therefore, is an experiment in which the hypothetical attentional spot-light can arrive at the position of the target before stimulus exposure, and/or can be sharply focused in advance. This can be done by precuing the position of the impending target. To give the early-selection view a fair chance, the cue-display interval (i.e., the stimulus onset asynchrony or SOA) has to be large enough to permit search to terminate or to allow the complete narrowing of attention to the target position before the target appears. Previous research suggests that such a process may take an appreciable amount of time, in the order of 150 msec (see, e.g., Eriksen and Collins 1969; and Hoffman 1975; see also Broadbent 1982: 270-271).

In experiment 2, we cued the position of the target by means of a bar-maker. The SOA was 150 msec and the stimulus exposure duration was 50 msec. This SOA seems to allow a fair test of the precategorical-selection views (see Eriksen and Collins 1969; and Hoffman 1975). These experimental conditions are not without problems, however. It is far from clear whether with the exposure durations used all useful eye movements are really prevented. Jonides et al. (1982) Rayner and Pollatsek (1983) and Rayner et al. (1983) for instance, showed that saccadic latencies are often smaller than 150 msec. If subjects make useful eye movements to the position of the target, distracters close to the target fall on more favourable retinal positions than distracters further removed from the target (see also the General introduction). Accordingly, this experiment may be biased in favour of the precategorical-selection views and against the postcategori- Cal-selection view.

There was a number of interactions in our first experiment, for present purposes not interesting, that might be attributed to the directionality of words. To avoid effects caused by the non-homogeneity of word-distracters, in experiment 2 we used a colour-colour instead of a colour-word Stroop task. Van der Heijden (1981: exps. 4 and 5) and Glaser and Glaser (1982: exp. 3) showed that these two tasks produce similar results. Three target-noise distances were used. The theoretically derived predictions for experiment 2 are identical to those for -experiment 1 (see fig. 1).

R. Hugenaar, A. H. C. uan der Heijden / Target-noise separation 171

Method

Apparatus The apparatus was the same as that used in experiment 1.

Subjects Twelve subjects who did not participate in the previous experiment, were recruited.

Six were female and six were male students. They all had normal or corrected-to-normal visual acuity and normal colour vision.

Stimuli and experimental conditions Three new sets of stimulus cards were prepared. The colours used were red, blue and

green. In each set, two of the three colours were relevant in that they could appear as targets as well as noise. The third colour only appeared as irrelevant noise. In set 1, red and green were relevant, and blue irrelevant; in set 2, red and blue were relevant, and green irrelevant; in set 3, blue and green were relevant, and red was irrelevant.

In each set three types of stimulus cards (or experimental conditions) were repre- sented: /

- single-colour stimulus cards containing only one of the relevant colours: the no-noise control condition;

- two-colour stimulus cards containing a relevant colour as the target and the other relevant colour as the distractor: the incompatible noise condition;

- two-colour stimulus cards containing a relevant colour as the target and the irrelevant colour as the distractor: the irrelevant or neutral noise condition.

The target patch was placed in one of four hour positions on an imaginary clock face with a diameter of 2.19 degrees. The hour positions were one, five, seven and eleven o’clock. On the two-colour cards, target-noise separation was varied by positioning the noise patches two, four or six hour positions away from the target. The noise patches were always at the other side of the centre. Fig. 4 serves to clarify the stimulus construction. Each set contained 48 two-colour stimulus cards, representing the factorial combination of 2 relevant colours x 4 target positions x 3 distances x 2 conditions, plus 8 single-colour stimulus cards, representing the factorial combination of 2 relevant colours x 4 colour positions. To increase the number of observations of single-colour stimuli, two copies of the single-colour cards were presented. In total, there were 64 stimulus cards (48 + 2 X 8) per set.

Each patch had a diameter of 0.56 degree. The distances from centre to centre between the patches were 1.09, 1.89 and 2.19 degree, respectively.

For each set of stimuli 64 bar-marker cards were prepared, one for each stimulus card. The bar-marker had the shape of an arrow and was drawn in black ink. It pointed outwards from the centre of the visual field (like the hand of a clock). The arrow subtended 0.52 X 0.09 degree. The pointed end of the arrow was separated from the edge of the colour patch by 0.32 degree.

172 R. Hagenaar, A. H. C. van der Heijden / Target-noise separation

0

,,.-- I

‘, ‘..._.I’

Fig. 4. Construction of the stimuli in experiment 2: (a) possible positions of the distractor colour patches (dashed 0) given a particular location of the target colour (0); (b) example of a stimulus card: target top right, distractor left and at the largest distance.

Design The 12 subjects were randomly assigned to three subgroups with the restriction that

each subgroup contained two males and two females. Each group saw one of the three sets of 64 stimulus cards.

Each subject saw a set three times, each time in a different random order. The presentations were separated by short rest periods. RTs on correct trials only were included in the analysis.

Procedure The subjects were tested individually in a moderately illuminated room. We asked

the subjects to initiate exposure of bar-marker and stimulus any time after they clearly saw the fixation cross. The bar-marker was displayed for 150 msec. The stimulus appeared immediately after bar-marker termination for 50 msec. The subjects were instructed to name the colour of the patch indicated by the bar-marker and to ignore the other patch, if present. The instruction emphasized both speed and accuracy.

Prior to the beginning of the experiment proper, the subjects received 24 practice trials to familiarize them with the stimuli and the task. They were explicitly told what the colours (and allowable responses) were.

Results

The results which are relevant for the issue under investigation are presented in fig. 5. The data have been collapsed across colour set and target position. An analysis of variance was performed on the mean RTs for the colour-colour stimuli, with condition (neutral or incompatible) and target-noise separation (1.09, 1.89 or 2.19 degrees) as within-subject factors, and set of relevant colours (three levels) as a between-subjects factor. The effect of conditions was highly significant (F(1, 9) = 118.41; p -C 0.001; the mean RTs for the neutral and incompatible conditions were 500 and 524 msec, respectively). The main effect of distance (F(2, 18) = 1.99) was not significant, and the interaction of distance by condition (F(2, 18) = 0.67) was far from significant. Also no effect of stimulus set (F(2, 9) = 0.62) has been found.

R. Hagenaar, A. H. C. uan der Heijden / Target-noise separation 173

0

f 560 -

c .-

& 540 -

520 -

500 - o-sb- neutra 1

8S

480 -

I I I 1.09” 1.89’ 2. lYO

,

Fig. 5. Mean RTs for colour-naming in the neutral and incompatible conditions as a function of target-noise separation; S = single (no-noise) condition (experiment 2).

Two-tailed t-tests for correlated observations showed that the single-target condition differed significantly from the neutral condition (t(l1) = 2.26, p < 0.05) and from the incompatible condition (t(l1) = 7.10, p < 0.001). The mean RT for single-colour stimuli was 491 msec.

The error rate was too low (less than 2% of the responses) to allow a meaningful analysis of errors.

Discussion

The outcome of this experiment is straightforward; it nicely replicates the outcome of experiment 1. As is evident in fig. 5, even when subjects know the position of the target colour in advance, (1) the presence of any other colour slows colour-naming of the target (that is, mean RTs in the single-colour condition are shorter than those in the other two conditions), (2) this delay is larger for incompatible than for neutral colour-colour combinations, and (3) these effects are independent of target-noise separation. The results of the analyses of variance confirm these conclusions. A highly significant main effect of condition was found, but there was no main effect of spacing nor a condition by spacing interaction. This is exactly the pattern of results depicted in fig. lc. In other words, the results fully support the postcategorical-selection view, whereas they do not lend any support to the perfect and the imperfect-precategorical- selection views. (The slight and non-significant decrease in.mean response times with distance from the target for incompatible stimuli can easily be accounted for by incidental eye movements made by some subjects; also colour sensitivity decreases with increasing distance from the fovea.)


General discussion

Many theorists consider selective attention to be like the beam of a spot-light. In their view, selective attention and the processing (that is,

‘identification) of information are interdependent; information within the beam of selective attention is processed in detail, and information outside the beam is not processed or receives only gross preattentive processing. Experiments in which supposed identity-dependent interference or facilitation, that is, interference or facilitation due to the categorical nature of a to-be-ignored object, decreases with increasing target-noise separation, are often cited as evidence in favour of these views. In the General introduction, we critically discussed this evidence. It appeared that none of these experiments really supported the beam-of-spot-light ‘view. For all relevant experiments, there were rea- sons to assume that increasing target-noise separation was confounded with decreasing visual acuity for the noise elements. Therefore, the apparent decrease in identity-dependent interference or facilitation can be accounted for in terms of decreasing visual acuity (see Gatti and Egeth (1978) and Merikle and Gorewich (1979) for similar conclusions).

The two experiments reported in this study present a first attempt to disentangle the two variables confounded in the earlier research: physical spacing and distance from the fovea. Target and noise elements were positioned on the circumference of an imaginary circle around the fixation point. If subjects make no useful saccadic eye movements, this way of stimulus presentation guarantees positions of equal visual acuity when target-noise separation is varied.

The major findings of experiment 1 were a significant delay in colour-naming due to the presence of incompatible colour words, and no effect of separation. The argument that the absence of an effect of spacing might be a consequence of search or insufficient time for focusing selective attention, is adequately refuted by the results of experiment 2. In that experiment, bar-markers were used to precue the position of the target, and sufficient time was given to direct attention to the relevant position. Essentially the same results as in experiment 1 were obtained: a highly significant delay in colour-naming due to the presence of incompatible noise items and no effect of distance. In short, both experiments fail to provide any evidence that a spacing effect results from the operation of an attentional mechanism.

R. Hagenaar, A.H.C. van der Heijden / Target-noise separation 175

References

Bouma, H., 1970. Interaction effects in parafoveal letter recognition. Nature 226, 177-178. Broadbent, D.E., 1982. Task combination and selective intake of information. Acta Psychologica

50, 253-290. Colegate, R.L., J.E. Hoffman and C.W. Eriksen, 1973. Selective encoding from multielement

visual displays. Perception & Psychophysics 14, 217-224. Deutsch, J.A. and D. Deutsch, 1963. Attention: some theoretical considerations. Psychological

Review 70, 80-90. Dyer, F.N., 1973. Interference and facilitation for color naming with separate bilateral presenta-

tions of the word and color. Journal of Experimental Psychology 99, 314-317. Egeth, H., 1977. ‘Attention and preattention’. In: G.H. Bower (ed.), The psychology of learning

and motivation. Advances in research and theory, Vol. 11. New York: Academic Press. pp. 277-320.

Eriksen, C.W. and J.F. Collins, 1969. Temporal course of selective attention. Journal of Experi- mental Psychology 80, 254-261.

Eriksen, B.A. and C.W. Eriksen, 1974. Effects of noise letters upon the identification of a target letter in a nonsearch task. Perception & Psychophysics 16, 143-149.

Eriksen, C.W. and B.A. Eriksen, 1979. Target redundancy in visual search: do repetitions of the target within the display impair processing? Perception & Psychophysics 26, 195-205.

Eriksen, C.W. and J.E. Hoffman, 1972. Temporal and spatial characteristics of selective encoding from visual displays. Perception & Psychophysics 12, 201-204.

Eriksen, C.W. and J.E. Hoffman, 1973. The extent of processing of noise elements during selective encoding from visual displays. Perception & Psychophysics 14, 155-160.

Eriksen, C.W. and J.W. Rohrbaugh, 1970. Some factors determining efficiency of selective attention. American Journal of Psychology 83, 330-342.

Eriksen, C.W. and D.W. Schultz, 1979. Information processing in visual search: a continuous flow conception and experimental results. Perception & Psychophysics 25, 249-263.

Francolini, C.M. and H.E. Egeth, 1980. On the nonautomaticity of ‘automatic’ activation: evidence of selective seeing. Perception & Psychophysics 27, 331-342.

Gatti, S.V. and H.E. Egeth, 1978. Failure of spatial selectivity in vision. Bulletin of the Psychonomic Society 11, 181-184.

Glaser, M.O. and W.R. Glaser, 1982. Time course analysis of the Stroop phenomenon. Journal of Experimental Psychology: Human Perception and Performance 8, 875-894.

Hoffman, J.E., 1975. Hierarchical stages in the processing of visual information. Perception & Psychophysics 18, 348-354.

Jonides, J., D.E. Irwin and S. Yantis, 1982. Integrating visual information from successive fixations. Science 215, 192-194.

Kahneman, D., 1973. Attention and effort. Englewood Cliffs, NJ: Prentice-Hall. Kahneman, D. and D. Chajczyk, 1983. Tests of the automaticity of reading: dilution of Stroop

effects by color-irrelevant stimuli. Journal of Experimental Psychology: Human Perception and Performance 9, 497-509.

Kahneman, D. and A. Henik, 1981. ‘Perceptual organization and attention’. In: M. Kubovy and J.R. Pomerantz (eds.), Perceptual organization. Hillsdale, NJ: Erlbaum.

Kahneman, D. and A. Treisman, 1984. ‘Changing views of attention and automaticity’. In: R. Parasuraman and D.R. Davies (eds.), Varieties of attention. New York: Academic Press.

Keele, SW., 1973. Attention and human performance. Pacific Palisades, CA: Goodyear. Klein, G.S., 1964. Semantic power measured through the interference of words with color-naming.

American Journal of Psychology 77, 576-588.


LaBerge, D., 1983. Spatial extent of attention to letters and words. Journal of Experimental Psychology: Human Perception and Performance 9, 371-379.

Merikle, P.M. and N.J. Gorewich, 1979. Spatial selectivity in vision: field size depends upon noise size. Bulletin of the Psychonomic Society 14, 343-346.

Neisser, U., 1967. Cognitive psychology. New York: Appleton-Century-Crofts. Neumann, O., 1980. Informationsselektion und Handlungssteuerung. Unpublished Doctoral dis-

sertation, University of Bochum, FRG. ,’ Neumann, O., 1984a. ‘Automatic processing: a review of recent findings and a plea for an old

theory’. In: W. Prinz and A.F. Sanders (eds.), Cognition and motor processes. Heidelberg/Berlin: Springer.

Neumann, O., 1984b. ‘Die Hypothese begrenzter Kapazitlt und die Funktionen der Aufmerk- samkeit’. In: 0. Neumann (ed.), Perspektiven der Kognitionspsychologie. Berlin: Springer.

Norman, D.A., 1968. Towards a theory of memory and attention. Psychological Review 75, 522-536.

Posner, MI., 1980. Orienting of attention. Quarterly Journal of Experimental Psychology 32, 3-25.

Rayner, K. and A. Pollatsek, 1983. Is visual information integrated across saccades? Perception & Psychophysics 34, 39-48.

Rayner, K., M.L. Slowiaczek, C. Clifton and J.H. Bertera, 1983. Latency of sequential eye movements: implications for reading. Journal of Experimental Psychology: Human Perception and Performance 9, 912-922.

Shiffrin, R.M. and W. Schneider, 1977. Controlled and automatic human information processing: II. Perceptual learning, automatic attending, and a general theory. Psychological Review 84, 127-190.

Van der Heijden, A.H.C., 1981. Short-term visual information forgetting. London: Routledge & Kegan Paul.

Van der Heijden, A.H.C., 1984. Postcategorical filtering in a bar-probe task. Memory 81 Cognition 12, 446-457.

Van der Heijden, A.H.C., R. Hagenaar and W. Bloem, 1984. Two stages in postcategorical filtering and selection. Memory & Cognition 12, 458-469.

target-noise separation in visual selective attention

Documents