emotional facia emotional facial expressions and the unconscious activation of physiological...

7/27/2019 Emotional Facia Emotional Facial Expressions and the Unconscious Activation of Physiological Responses Expressio

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Emotional Facial Expressionsand the Unconscious Activationof Physiological Responses

BY

FRANCISCO ESTEVES

UPPSALA UNIVERSITY 1993


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Comprehensive Summaries ofUppsala Dissertationsfrom the Faculty of Social Sciences 40

Emotional Facial Expressionsand the Unconscious Activationof Physiological Responses

BYFRANCISCO ESTEVES

ACfA UNIVERSITATIS UPSALIENSISUPPSALA 1993


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Doctoral dissertation at Uppsala University 1993

AbstractEsteves, F. 1993. Emotional Facial Expressions and the Unconscious Activation of PhysiologicalResponses. Acta Univ. Ups., Comprehensive Summaries of Uppsala Dissertations from the Faculty ofSocial Sciences 40.54 pp. Uppsala. ISBN 91-554-3182-8.

TI1e possibility of unconscious processing of facial stimuli was the focus of the empiricalstudies presented in this thesis.

Based on an evolutionary perspective, it is argued that threatening faces, i.e., faces withangry expressions, can be considered a case of fear-relevant stimuli, and that an early detection andthe activation of appropriated physiological and behavioural responses to angry faces has had animportant survival value. Thus, it is argued that angry facial expressions can be processed at anunconscious level and activate emotional responses.

In Study I, a backward masking procedure was developed in order to obtain a conditionthat prevented the subjects from becoming aware of the facial stimuli presented. In Studies II and III,a Pavlovian conditioning procedure was employed in order to study the possibility of unconsciousprocessing of facial expressions and activation of physiological responses. Thus, in Study II it wasshown that, af ter a conditioned response to an angry face has been established, it is possible to elicitphysiological responses to that face even when the subjects were not aware of the stimuli presented. InStudy III, associative learning was obtained when an angry face was used as the conditioned stimulusin conditions where the subjects were not aware of the presentation of the stimuli.

The present results support the idea that angry facial expressions are especially sensitive tounconscious processing.

Francisco Esteves, Deparlment ofClinical Pl)!chology, Uppsala University, Box1225, 75142 Uppsala,Sweden.

Francisco Esteves 1993

ISSN 0282"7492ISBN 91-554-3182-8Printed in Sweden by Reprocentralen, HSC, Uppsala 1993


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To my parents


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This thesis is based on the J!UWW1H"' papers, which 'INiH be referred to in the texttheir Roman numerals:

n. ' " " ' ~ - " . W ' . " L'lillOt:I!!. u. and A. elicited' .rm,fiitin"'"rl skin conductance responses to masked facialeXJpn::ssions. Ilf.111'1.!u.n'n and Emotion.

Study HI. Esteves, F., Parra, C., Dimberg, U. and Ohman, A (1993).Nonconscious associative learning: Pavlovian conditioning of skinconductance responses to masked fear-relevant facial stimuli.~ - ' " ' ' ' ~ h n n h " ' ~ ' " ' A ' n m ' (In press).

Reprints of Study I were made with permission from the publishers.


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TABLE OF CONTENTS

1. INTRODUCTION1.1. Human facial expressions1.1.1. The human face1.1.2. Is face perception a unique process?1.1.3. Facial emotional expressions1.1.4. Decoding of emotional expressions under degradedexposure conditions1.1.5. Angry facial expressions as fear-relevant stimuli1.1.6. Summary1.2. Unconscious processing1.2.1. Information processing models1.2.2. Unconscious perception1.2.3. Unconscious physiological activation1.2.4. Unconscious associative learning1.3. Clinical relevance1.4. Backward masking

2. THE EMPIRICALSTUDIES2.1. The aim of the studies2.2. General method2.2.1. The common features2.3. Study I2.4. The conditioning studies2.4.1. The common method2.4.2. Study II2.4.3. Study III

3. GENERAL DISCUSSION3.1. Unconscious processing of angry faces3.2. Concluding remarks

4. REFERENSES

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ACKNOWLEDGEMENTSThe present studies were carried out at the Department of ClinicalPsychology, University of Uppsala. I am grateful to an the staff of theDepartment for the good working atmosphere and the positive support mywork was during these years.Allthough the inaccuracies that may appear in this ofmyown responsibility, the work presented here is the of a team. I amgrateful to an those that have contributed in one way or another to this team.Among h e m I am grateful to:Arne Ohman, my and friend. Hisknowledge have been indispensable support during thisadventure. It has been a pleasure running with you, Arne.- Cristina Parra, my friend and co-author. Her companionship andcoHaboration have always been present, despite the distance.- Ulf Dimberg, c o ~ a u t h o r and friend, for his encouraging support and who hasintroduced me to the mysteries of the psychophysiology laboratory.- Anders Flykt, colleague and friend for his optimism and positive attitude.-The people from the Technical Unit, especially Lars-Erik Larson, Karl-ErikGryden, Lars Backstrom and Kurt Wikman for aH the hours trying to findsolutions to my many strange requests.- Joaquim Soares for technical assistance.For an the exceHent comments and suggestions to a first version of thissummary I want to thank Berit Scott and Staffan Sohlberg. A am also gratefulto Les Shaps for p r o o f ~ r e a d i n g my English.My gratitude is also extended to an my colleagues at the Department, with aspecial t h a n ~ ~ to the "old" friends: Lene, Kerstin, Christina H., Alina, Janne,Raimo, and Orjan Sundin.Last, but not least, I would like to express my gratitude to my family andfriends, those Hving near and those far away, for always having supp0rted me.Uppsala, October 1993Francisco Gomes Esteves


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1. INTRODUCTION

1.1. HUMAN FACIAL EXPRESSIONS1.1.1. The human face

The interest in the scientific study of the human face as a PS'vCtlto!


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feelings and states of mind to feHow human beings. It is also thr.rmrrh the face that weinterpret and infer the affects and moods of others. faces are the mostimportant part of the body in influencing and regulating social interactions

For example, the use of eye contact is an important sodal skill it canbe noted that faces also are related to verbal communication. It is through the mouththat we speak, and the reading of the lips and mouth movements facilitates thecomprehension of (Bruce,

One intriguing aspect of face perception is our advanced ability todiscriminate different faces. Thus, we can recognize despite physicalchanges such as wearing eyeglasses or beards, and we can recognize we havenot seen for many years. A hundred years ago, Francis Galton, one of the firstexperimental psychologists interested in the study of the human face, commented onour ability to out small details, and to discriminate accurately between differentfaces, despite the great similarity of facial traits (Galton, 1883/1928).

This ability in facial discrimination, corroborated by the results of empiricalstudies on face perception and the existence of prosopagnosic patients, has led someauthors to speculate that the face is a unique visual stimulus, and that we areequipped with a special face-processing mechanism (Yin, 1978; Whiteley &Warrington, 1977).

Basically, four different arguments for this uniqueness have been presented.The first one is based on developmental studies. Goren, Sarty, and Wu (1975)showed that neonates, some minutes after birth, paid more attention to faces than toother stimulus a result later replicated by Dziurawiec and Ems (Ellis, 1990).In a study with neonates with a mean age of 36 hours, Field, Woodson, Greenberg,and Cohen (1982) showed that newborn infants could discriminate differentemotional facial expressions. Meltzoff and Moore observed thatnewborns could discriminate facial gestures and had an abiHty to imitate adultexpressions. Thus, these infant studies presented data suggesting a strong innatecomponentin the perception of faces and facial expressions.

The second argument is based on perception and memory studies thatcompared faces to other visual stimuli. An of this tradition are the inversionstudies. Yin showed a impairment in facial discrimination than in


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discrimination of other visual g., houses) when the stimuli were presentedupside-down. and Diamond obtained a simHar inversion effect with 10- ..,,u -'"""' children but not with 6- or 8-year-old which attributed to thedevelopment of an ability to encode configurational of a face around 10 yearsof age, while younger children appeared to more on detail information. Theseresults have been interpreted as evidence for the existence of different processes inthe perception of faces to other classes of objects, thus some kindof unique skin for face Diamond andobtained comparable inversion effects with another class of stimuli,whenby inversion of the stimulus is related to and in a general sense, we anbecome "experts" in face recognition. studies (e. g., Freedman & Haber,

have also been used to demonstrate that faces are special. For example,Bahrick, Bahrick, and Wittlinger (1975), showed that subjects performed extremelyweB in the recognition of high school classmates after almost 50 years. However, it isdifficult to compare this kind of learning condition, involving a prolonged exposurefor several months/years, to the learning of other classes of visual stimuli which couldbe considered equivalent. Laboratory studies have shown contraditory findingsDeffenbacher, 1986). For example, Goldstein (1977) obtained high recognition ratesfor briefly presented pictures of strangers after long intervals; however, morecontrolled experiments (e. g., Church & Winograd, 1986; Faw, 1990) have failed toconfirm this special memory for faces.

A third argument for the uniqueness of face perception is the existence ofprosopagnosia. This is a neurological syndrome characterized by an inability torecognize familiar faces (Bodamer, 1947). This argument would be very strong if thespecificity of the syndrome could be shown, i.e. if the impairment would be restrictedto faces and not include other visual stimulus dasses. However, as it is a raresyndrome, and as cerebral lesions are never exactly the same, it has been difficult toprove the specificity of prosopagnosia. The majority of the clinical cases presenteddid show in recognizing other classes of objects (e. g., animals), which hasled some authors to consider the syndrome as a manifestation of a more generalneurological dysfunction, not specific to faces (e. g., Damasio, Damasio, & VanHoesen, 1982), possibly related to a certain degree of stimulus complexity (De Renzi& Spinnler, 1966; Warrington & James, 1967). However, there are at least tworeported cases in the litterature that seems to have an exclusive deficit for faces. DeRenzi (1986) reported one patient 4) who did not show other impairments,thus failing to support the thesis of a general dysfunction. McNeil and


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also reported a case of a who could discriminate betweenpictures of his own but '"'""u."u'"' differentknown faces. Furthermore, studies with other have shownsubtle impairments of face recognition dissociated from impairments on therecognition of other stimuli,(Tzavaras, Hecaen, & LeBras,

the existence of a face-specific deficit

another dass of studies that has been invoked to thespecificity of the face are those that measured the cortical of monkeysexposed to facial stimuli. For example, Rolls (1984) found a number of neurons in thetemporal lobe and in the amygdala of the rherus monkey that r e ~ ; p o m a . e ato faces.

To summarize these it appears difficult to argue definitively for theexistence of a unique skin of face perception in the sense advanced Yin (1978),especiaHy if this uniqueness is interpreted as implying a mechanism for theperception of faces working in a different way than other visual recognition systems(Hay & Young, 1982). Instead, some authors have proposed a weaker definition ofuniqueness, what Hay and (1982) caHed specificity, implying a separaterecognition system, but not requiring qualitatively different perceptual processes (e.g., Bruce & Young, Ellis & Young, 1989; Levine, 1989). This idea of faceprocessing being organised into a separate fits in wen with a modularity model(Fodor, 1983; Marr, 1982) and with the idea of "gnostic areas" proposed by Konarski(1967). Furthermore, the experiments with monkeys that showed that some neuronsresponded selectively to faces (RoH:s, 1984) indicate that there is a neurological basisfor some kind of specificity. However, although the "uniqueness" might be difficult toprove, the innate component supported by some developmental studies (e. g. Gorenet al., 1975) is a strong argument for considering face processing to be very special(Morton & Johnson, 1989). Tzavaras et al. (1970) related this innate attention-caningcharacteristic of facial stimuli to the phenomenon of imprinting. Al.so, Bushnell, Sai,and Mullin (1989) observed that neonates with a mean age of 49 hours couldrecognize their mothers'face. The prosopagnosic syndrome, is an importantpiece of evidence. The "pure" cases (De Renzi, 1986; McNeil & Warrington, 1993)strongly recommend some caution in discarding the ~ r " ' " i * ' i , . i i r . r argument (see alsoEUis& Young,

on face perception to perception of or words. However,


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some sceptic voices (e. g., Davidoff, 1986), most authors agree that the human faceconstitutes a very stimulus. One of this speciality is thecentral role of the face in social interactions and its to emotionalexpressions. it is the fact that the face conveys information about emotionalexpressions and provides a vehicle for nonverbal communication or, as Buck

it, that it also involves communication from information present within the skin,that makes the face a unique stimulus class.1.1.3. Facial emotional ' n > r e : s s i ~ l ' I I I S

The importance of emotional facial expressions in nonverbal socialcommunication was first in his book The expression of

facial expressions in an evolutionaryperspective, he emphasized the biological, innate characteristics of facial expressionsin humans and other primates.

Evidence for a genetic loading, both in the ability to produce different facialexpressions and in the ability to decode and recognize these expressions, comes fromdifferent types of empirical studies (see Ohman & Dimberg, 1984, for a review).Cross-cultural studies (e. g., Ekman, 1982; Ekman et al., 1987) have shown thatmembers of different cultures produce the same facial expressions when experiencingdistinct emotions, and that the interpretation of some basic emotional expressions isuniversal also. This universality, showing a consistent pattern over different culturesand times, has been a subject of debate since Darwin, and some researchers havedefended a culture-specific position (e. g., Kline berg, 1940). However, despite somerecently presented objections (Fridlund, 1992), some consensus now seems to havebeen reached regarding the universality of certain emotional facial expressions(Ekman, 1992; Oster, Daily, & Goldenthal, 1989; Pitcairn, 1989).

Another Hne of evidence suggesting an innate basis of emotional facialexpressions comes from developmental studies. Neonates have a to imitatefacial movements in the first days of life and, after only a few weeks, infants canproduce distinctive emotional displays in social interactions with their caregiver (seeFridlund, Ekman, & Oster, for a review). The observation of blind and blinddeaf born children confirms this innate characteristic. They can display some facialemotional expressions, although their repertoire appears more limited than that ofnormal child Daily, & Goldenthal, Finally, studies of other primateshave documented that they use similar facial displays in social interactions (Brothers,


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and that suchmaintenance of social hierarchies

From ancan be relatively

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are important in the establishment and

that genetic programsto modification programs

environmental input in their transformation to neural programs capable ofbehaviour Some social which constant

stimulus-response relations, were to be under the control of relativelydosed genetic programs. This would be the case for behaviour that is directed tomembers of the same (intraspecific which because of its survivalrelevance should be more dependent on dosed genetic programsSexual activity and parent-child relations, for example, should be expected to becontroHed by closed genetic programs. Furthermore, because the ecology of smallgroups has remained stable during human evolution, it appears reasonable to assumethat relatively dosed genetic programs may regulate face-to-face interactions(Ohman & Dimberg, 1984). Studies with nonhuman primates raised in socialisolation also support a relatively closed program for expressive behaviour (Geen,1992).

A consequence of this reliance on dosed genetic programs could be thedevelopment of a specific system for the processing of facial affect Indeed, severalauthors have proposed the existence of such a system. For example, Bruce andYoung (1986) proposed a system to analyse emotional expressions, acting in paraHelwith the recognition of identity. Also, Ley and Strauss (1986) proposed anindependent mechanism for the recognition of emotional expressions. Thus, althoughsome authors have proposed that the perception of different emotional displaysinfluences face recognition (e. g., Galper & Hochberg, most researchers seemto accept the independence of these processes (Bruce, 1988; Calis & Mens, 1986).For example, Konorskli (1967) considered face recognition and the analysis ofemotional expressions as two independent categories of visual stimuli, which hepostulated to be processed separate "gnostic areas". Furthermore, studies withrhesus monkeys have shown that different neurons in the brain are specialised onidentity recognition and on facial Finally, dinka] studieshave also provided support for the existence of a specific facial affect system. Kuruczand Fe]dmar found evidence for the impairment of facial affect recognition

Rapcsak,


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Kaszniak, and Rubens reported the case of a with a selective

A consequence of the proposed in thesection is that an important survival value should be inherent in the to decode

the human face, It is easy to understand theadvantage of our prehistorical ancestors to possess an correctinterpretation of, for example, a threatening facial expression. This would beimportant, both when encountering a stranger which could be a potential enemy, andin situations within the own group, in the appraisal of relative dominance (cf.Keating, 1985). It should be noticed that this interpretation does not necessarilyimply labeling, indeed this appraisal can be considered nonconsdous 1988;Frijda, Kuipers, & Schure, 1989). In fact, such an ability to recognize emotionalexpressions without any conscious processing was postulated already(1872).

Darwin

This special ability should allow the decoding of facial expressions even underdifficult viewing conditions. Thus, one approach to examine the interpretation ofemotional expressions is to study recognition in situations that are constructed todegrade perceptual distinctiveness and enhance ambiguity.

Some studies have investigated the recognition of different facial expressionsunder conditions of degraded stimulus exposure. For example, Hager and Ekman(1979) studied recognition of emotional expressions when the subject was at arelatively long distance (30-45 m) from the stimulus display. They found that at leastcertain expressions were quite accurately identified despite the distance, bothlive models and pictures were used.

Another dimension of degraded stimulus input is the reduction of exposuretime. Kirouac and Dore (1984) found that subjects could differentemotional expressions under conditions of very brief exposures ms). AlsoMcAndrew (1986), in a cross-cultural study, obtained good recognition of differentemotional expressions exposed very briefly ( 1 2 ~ 2 5 for both American andMalaysian


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WaHbot examined the effect of reduced resolution, reducedcontrast resolution, and reduced picture size on the recognition of differentemotional facial expressions. He concluded that recognition of the facial expressionswas insensitive to the degradation of the stimuli within a very large range of

In summary, there is empirical for a special ability to decode facialexpressions even when they are presented under poor perceptual conditions. Takinga step it could be asked if this decoding process awareness. Indeed,given the evolutionary perspective presented above, it would be reasonable toassume that some emotional expressions could be decoded automaticaHy, and thatappropriate behavioural responses could be activated without conscious appraisal ofthe facial expression. For example, faces expressing anger or that could convey somekind of threat should be especiaHy to eHcit responses governed relativelydosed genetic programs.1.1.5 as fear-relevant stimuU

In the beginning of the seventies, the traditional learning theory, whichassumes that learning of new associations between stimuli was independent of thestimuli involved, was criticized. Seligman (1970), in particular, refuted this"equipotentiality premise" and postulated that, because certain associations havebeen important to survival, an species inducting humans are biologically predisposedto learn some associations more easily than others. According to Seligmanone consequence of this predisposition could be observed in human phobic fears. Heargued that natural selection has resulted in a biological preparedness to easilyassociate threatening stimuli/situations with avoidance and escape responses, i.e.,with fear. In fact, dinkal observations showed that most phobic stimuli can be related!to some potential phylogenetic (see Ohman, Dimberg, & Ost, 1985, for areview).

This appHcation of the preparedness theory to human fears and phobias hasbeen studied empirically by and co-workers 1979; Ohman,Dimberg, & in the context of aversive Pavlovian conditioning. In a seriesof studies, autonomic responses to stimuH that could be considered fear-relevant inthe sense proposedby SeHgman were compared with responses to fear-irrelevantstimuli For example, of snakes and (fear-relevant) were comparedto of flowers and mushrooms (fear-irrelevant). The most consistent finding


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was autonomic responses toconditioned fear-relevant stimuH showed an elevated resistance to extinction

L A A U " - ' ' - ' ~ , u there were some negative results in the toreplicate some of these findings e. g., 1987), in general, the enhancedresistance to extinction after conditioning to fear-relevant stimuli can be considereddemonstrated (see Ohman, for a review).

Of special interest for this thesis were the experiments that used emotionalfacial expressions as conditioned stimuli It was assumed that angry facialexpressions could be considered a fear-relevant stimulus for social In fact,enhanced resistance to extinction after conditioning was obtained when angry facialexpressions were used as the conditioned stimuli, but not when the CSs werefacial expressions (Ohman & Dimberg, 1978).

That angry facial expressions might have an evolutionary relevance has alsobeen documented in other studies, both with humans and with nonhuman primates.In a study with rhesus monkeys, Sackett (1966) found that monkeys reared inisolation were especially activated by pictures of threatening faces, thus indicating aninnate recognition mechanism behind the activation effect. Schwartz, Izard, andAnsul (1985) observed that five-month-old infants showed more avoidance to angryfaces than to expressions of fear and sadness. A curious vestige of the use of angryfaces was described by Eibl-Eibesfeldt and Sutterlin (1990). They found thatthreatening facial expressions were encountered quite frequently on stone sculpturesin old churches, which they interpreted as a means of driving away evil spirits anddemons. The idea that the sign vehicles for the expression of angry displays could befound in the art work of different cultures inspired Aronoff, Barclay, and Stevenson(1988) to try to identify the necessary features for the expression of threat, which theyfound to be associated with angularity and diagonality in visual stimulus patterns.1.1.6. Summary

In this section, evidence suggesting that the human face is a special perceptualstimulus has been reviewed, both with respect in our ability to recognize individualsand in our capacity to decode the affective messages conveyed facial expressions.Furthermore, it has been argued that both the expression of different emotionaldisplays, and the interpretation of facial emotional expressions rest on mechanismsfor which genes provide an important source of variance.


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This genetic variance would reflect selection pressure on functional behaviourover eons of time. As a consequence, the resulting mechanism would be robust andlikely to withstand conditions of degraded informational input. Furthermore, thesemechanisms would be likely to function automatically with no need for consciousappraisal of the stimulus. A main purpose of this thesis is to examine if angry facialexpressions are especially sensitive to automatic, unconscious mechanisms. In thenext section, data suggesting the existence of unconscious perceptual processes willbe presented, as viewed from an information-processing perspective.1.2. UNCONSCIOUS PROCESSING1.2.1. Information processing models

Broadbent (1958) presented a model of the human information-processingsystem which had an enormous impact on subsequent research in experimentalpsychology. The model focused on the role of selective attention conceived as a filter,letting some information through for further processing in a sequential processingchannel with limited capacity, while most of the stimulus information was filtered outand ignored. Subsequently, several different models have been proposed in attemptsto integrate new empirical findings (e. g., Cowan, 1988; Ohman, 1979). In general,following the model proposed by Shiffrin and Schneider (1977), two modes ofinformation processing have been distinguished, an automatic, involuntary,preattentive mechanism and a top-down, voluntarily-controlled process. Thus,Shiffrin and Schneider (1977) differentiated between automatic and controlledprocessing, Ohman (1979) between preattentive and capacity-limited processes, andMarcel (1983) between conscious and unconscious processing. Although thesedichotomies do not overlap completely, in general, they have been regarded asreferring to the same phenomena (e. g., Schneider, Dumais, & Shiffrin, 1984). Thus,these models suggested the existence of an initial phase of human informationprocessing that would be characterized by automaticity and parallel processing acrossdifferent sensory channels, and that would be independent of volition and awareness(Schneider, Dumais, & Shiffrin, 1984).

1.2.2. n ~ o n s c i o u s perceptionThe idea t ~ a t a substantial part of the information presented to our senses is

not perceived at the conscious level is not a new one. Three hundred years ago,Leibniz was the first to postulate that our behaviour could be influenced by


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During the fifties and sixties several

the idea thatwith

it runs counter to thereason and

conducted onwhich claimed

such conclusions were called into question in an influentialHe showed

had not beencriteria were necessary before empirical of unconscious

perception could be claimed. Although Eriksen' s criticisms were very influential andstill are considered valid by some g., Holender, in the last two decadesseveral authors have emphasized the importance of unconscious perceptualprocesses in many psychological contexts g., 1981; Greenwald,

Nevertheless, the empirical work on unconscious perceptual processes hasresulted in contradictory findings. As Cheesman and Merilde (1986) noted, the mainproblem has been the lack of an accepted measure of conscious experience. Thus, ina review of the literature, they found that studies that employed a very stringentmeasure of awareness in general have failed to find unconscious effects, while thepositive results have been obtained in studies that used more subjectively definedmeasures of awareness (Cheesman & Merilde, 1986). However, as Merilde andReingold (1992) accurately noted, a perfect objective measure of awarenesspresupposes two conditions which are practically impossible to satisfy. Thus, theputative measure must be both exhaustive, L e. be sensitive to all consciousexperience and exclusive, i. e. be only sensitive to conscious experience withouteliminating unconscious information. However, a more reasonable assumption is toaccept that any measure of perception could be affected by both conscious andunconscious processes (Merilde & Reingold, 1992). As out Bowersthe use of very stringent criteria exclude unconscious perception by definition.Instead, Cheesman and Merikle (1986) proposed the use of a criterion.They defined subjective threshold as the level of discriminative responding at whichsubjects claim to perform at the chance level (Cheesman & Merilde, Despitethe risk of subjectivity, this criterion is closer to the interesting differentiationbetween what the perceivers know and "what they know they know" (Fowler, 1986),


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and seems to have been accepted&

unconsciousFinaHy, in studies withwith thethey could not see.

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In summary, :it can be conducted that unconscious perceptionthat we can be influenced by stimuH we are not aware ofusing Bowers terminology, Stimuli that are nPlH" ' " ' l iV f " f f l l

there are

severalTP I 'P ;M . < ' been

could

be noticed that(Greenwald, of unconscious influence. One refers to what Greenwaldcalled the auentionless sense, stimuH that fan outside of selective attention or stimulithat are perceived but not noticed 1984). The other mode refers to stimuHthat have been consciously perceived at some point but that are not available forintrospection. Such stimuli thus are not appreciated as influentialAlthough the second mode also can be interesting, for example, concerning memorybias in dinical groups, it is the first mode of unconsdous influence I refer to in thisthesis.

Physiological measures have been used before in studies intending to detecteffects of unconsdous processing. For Corteen and Wood andCorteen and Dunn used a dichotic Hstening to demonstrate more

sklin conductance responses (SCR) to shock-associated words than to" ' ' " " " " ' ~ in the nonattended ear task.

/)


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"'"''!'."'""'"''-' shock-associated words when the left but not the right ear was used asthe nonattended channel. \ '

In a series of aversive Pavlovian experiments, fear-relevantpictures (snakes and as conditioned and Soaresdemonstrated that it was possible to elicit SCRs to previously conditioned fear-relevant stimuli even when awareness of a backward

restricted to fear-relevantthat it is possible to elicit autonomic responses to stimuli of which theremained unaware (see also Dawson & ScheU, 1985).1.2.4. Unconscious associative leamilng

The possibility of unconscious learning has been tested for some years. In aseries of experiments, Reber and co-workers Reber, 1989, for a review) used anartificial grammar procedure to show thatand later discriminate between correct

being able to verbalise the rules used. Lewicki and co-workers (Lewicki,1988; Hill, Lewicki, Czyzewska, & SchuHer, 1990) in a series of experimentshave shown that subjects, exposed to covariations between experimental events they

were not able to report, could use this covariation to improve their task performance,and thus indirectly show that they could apply knowledge that had been implicitlylearned. Although these experiments have been criticized (e. g., Brody, 1989;Perruchet & Pacteau, 1990), and some authors claimed that some awareness 'mighthave been involved (e. g., Perruchet, Gallego, & Savy, 1990), these results can not besimply dismissed.

Studies with neurological patients, too, have shown implicit learning effects.For example, Weiskrantz and Warrington (1979), working with amnesic andde Haan, Young, and Newcombe (1987) with a prosopagnosic patient, obtainedlearning effects even the subjects denied knowing what they were

In the context of Pavlovian conditioning, the role of cognitive factors has beendiscussed since Pavlov. Breaking with a rationalistic where consciousnesswas a central aspect, Pavlov (1927), after what he described as a mental conflict,became committed to an objective, physiological approach to conditioning in whichcognitive aspects were deliberately ignored. To view classical conditioning as

among


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psychologists) of classical conditioning as mechanical and mindless. However, duringthe last 20 years another view of Pavlovian conditioning has emerged, definingclassical conditioning as a more complex learning process, based on multipleassociations between events in the environment (Ohman, 1988; Rescorla, 1988).Contrary to the traditional view, this learning process is supposed to demandadvanced cognitive processing and, for humans, conscious mechanisms are~ t o be necessary (Dawson & s c h e l ~ 1 9 - 8 5 ; - 8 ~ ; ~ ; 1 9 8 3 } --

In fact, the first Pavlovian conditioning experiments in humans that claimed todemonstrate unconscious learning (e. g., Lacey & Smith, 1954) were later criticized(e. g., Dawson, 1973). Dawson and co-workers demonstrated that, with a moreadequate a s s e ~ ~ I l ! e n t .of ~ ' ~ ' : ! ! ! : ~ . ! 1 - E s s , conditioning effects were apparent only in

- 8 u b j ~ c t s that could. ~ ; ; ~ c t l y r e p ~ 7 t the contingency between the unconditionedstimulus (US) and the CS (Dawson, 1970; Dawson & Biferno, 1973; Dawson &Reardon, 1973). Using a continuous measurement of the subjects' expectancy of theUS, it was demonstrated that differential SCRs to the reinforced and thenonreinforced stimuli were obtained only after the subjects became!J._ware of the CS-US contingency (e. g., Biferno & Dawson 1977; Ohman, Ellstrom, & Bjorkstrand,1976). Based on these results, Dawson and Furedy (1976) postulated that awarenessof the CS-US relationship was a necessary but not sufficient condition for humandifferential classical conditioning. This is still the common view among researchers inhuman Pavlovian conditioning (Davey, 1987; Dawson & Schell, 1985).

In summary, this section introduced some arguments for the existence ofunconscious cognitive processes. First, it has been argued that we can be influencedby stimuli that are not consciously perceived; for example, that physiologicalresponses can be activated without a conscious appraisal of the eliciting stimulus.Second, it has been argued that there exists some evidence for unconscious orimplicit learning, despite the general denial of this possibility among Pavlovianconditioning theorists.

The possibility of unconscious information processing, together with thebiological relevance of angry facial expressions documented in the first part of theintroduction, leads to the central empirical question of this thesis: To demonstratethat angry faces can be processed unconsciously, and that this results in the elicitationof conditioned phys!ological responses and in associative learning.


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Before the description of the empirical work two issues wm be considered.First some clinical implications of unconscious are and then ashort introduction to visual backward is1.3. CLINICAL RELEVANCE

The approach presented here involvesstudies that constitute this thesis were not based on dinkal groups, but rather on

students, usuaHy considered a normal the study ofunconsciousbe elucidated.

An important aspect is related to theconcept, including different kinds of phenomena, but in most cases it can be said thatanxiety occurs in response to stimuli or situations that are perceived as threatening(Ohman, 1993a). In fact, it can be argued that the biological function of is tofacilitate the detection of threat in potentially dangerous situations (Eysenck, 1992;Ohman, 1993a). I f this is integrated within an information-processing perspective,assuming that (Dixon, 1981), it iseasy to agree with the view that early perceptual processes deserve special attention.

Although not an agree on the importance of unconscious processes for theunderstanding of anxiety (cf. Sacco & Beck, 1985), several authors have argued infavor of their importance. For example, Mathews and co-workers have shown anunconscious processing bias for anxiety patients to attend to threatening stimuli(Mathews, 1990; Mathews & MacLeod, The possibility of detectingthreatening stimuli automatically, based on simple stimulus features, is in accordancewith Zajonc's (1980) proposition that the affective evaluation of a stimulus does notrequire a conscious stimulus analysis. The work of LeDoux 1990), showing thatthere is a neurological basis for a subcortical activation of affective responses, givesfurther support to these approaches.

social phobics are especially sensitive to be evaluated others (Liebowitz, Gorman,Fyer, & Klein, 1985), angry facial expressions that imply some kind ofnegative evaluation should be particularly relevant to them (Ohman, JLJu.uuvL1985). Furthermore, as reviewed above, an early detection of this threat should


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!l ir.lll;iill11:1'1U1i!'i,:l, 22

facilitate the activation of appropriate behavioural and physiological responses andthe implementation of efficient coping strategies.

1.4. BACKWARD MASKINGThe visual masking paradigm has been used in many experiments. In general,

it refers to very short presentations of two stimuli, in temporal and spatial proximity.In the case of backward masking, the presentation of the masking stimulus interfereswitp the processing of a previously presented target stimulus.

Different theories have been put forward to explain this phenomenon and,'!',depending on t h e . ~ ~ J - ~ h e interference is conceptualized, they can be classified as

i ~ , ~ e g r a t i o n models o H ~ J r r u p t i o n models (Massaro, 1975). The integration theoriespostulate some kind of fusion, or combination of the neural representations of thetarget and the mask (e. g., Breitmeyer & Ganz, 1976; Eriksen & Eriksen, 1971).Other theorists have proposed some kind of interruption on the processing of thetarget caused by the presentation of the mask (e. g., Massaro, 1975). This is whatAverbach and Coriell (1960) called erasure of the target. A third line is to admit that

' - - ~ both integration and interruption processes occur, but that the kind of interferenceobtained depends on the exposure conditions, such as stimulus intensity or target-mask interval (Fox, 1978; Turvey, 1973).

The understanding of the phenomenon is further complicated by differencesbetween central and peripheral masking (Turvey, 1973) or between perceptual andconceptual masking (Loftus & Ginn, 1984; Potter, 1976). These differences will notbe analysed here, however, as our purpose was to interrupt processing of the targetstimulus before a complete percept was formed, i.e., before the subject becameaware of the target (Marcel 1983; Massaro, 1975). Concerning theperceptual/conceptual dichotomy, Potter (1976) suggested that conceptual maskingoccurred after the picture had been identified. I f by this she meant consciouslyperceived, then our masking in the unconscious conditions should be consideredperceptual. However, as Loftus and Ginn (1984) remarked, perceptual processingcan be disrupted both by peripheral and by central masking. Although this issue is notcentral to this thesis, we were more interested in central masking, i.e. masking causedby competition between target and mask for cognitive resources, than on peripheralmasking, and as it will be commented below, it seems that the masking effectobtained was more of central origin.


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2. THE EMPIRICAL STUDIES

2.1. THE AIM OF THE STUDIESIn the introduction some pnJp(JSi1:iOJ1S about facial stimuli that serve as the

basis of the research reported :in trus thesis were presented. First, the human faceconstitutes a special class of visual stimuli, in due to its communicative character...,. . - u u u , some facial reflecting basic emotions, areand recognized. Third, threatening faces, faces with angry eX]pre:ssions,considered a case of fear-relevant implying aconditions of degraded input. it has been demonstrated that, in the context ofPavlovian conditioning, aversively conditioned responses to angry faces show anenhanced resistance to extinction.

A second point of departure is provided by evidence suggesting that sometypes of stimuli can be processed at an unconscious level. In particular, it appearsthat il:t!t_


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2.2. GENERAL METHOD

Both used Pavlovian differential conditioning paradigms with skin conductance~ ~ ~ - ~ .. as the dependent variable. I, however, since its purpose was to

' - A


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The use of slides :in theis taken of the *",""'"""1

in addition to the advantage of some studies havereported quite good accuracy in the of emotional " " " ' ' r " ' . ~ ' " " ' n " cmnp,an::uto live stimuli (Hager & Ekman,

one after the other :in time but in the sameexJJmied immediately after each other

are notneutral faces have

two pictures were displayed,location. The two stimuli could be

offset of the to theonset of the mask) or with between target and mask. The concept of

i.e. the time interval between the onset of thetarget and the onset of the mask, provides an unequivocal specification of the target-mask interval. Thus, the SOA and the exposure times of the target and the maskprovide an exhaustive description of the temporal exposure conditions.

\

The reason for neutral faces rather than other stimulus patterns asmasking stimuli is that have similar luminosity to the target pictures and occupythe same spatial area. Furthermore, in the conditioning in which bothmasked and nonmasked stimuli were used and compared to each other, it is a dearadvantage that an stimuli belong to the same stimulus class.

2.3.STUDYI

Masking the face: Recognition of emotional facial expressions as a function of theparameters of backward masking.

The purpose ofthe recognition of emotional facial expressions in order to define the conditions ofstimulus presentation that are outside of awareness. Thus,for Studies H and HI.

I consisted of four different experiments. The general idea was topresent pairs of a r g e t ~ m a s k stimuli. The was the emotional face for which we


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wanted to determine thresholds ofThe masking conditions were

26

subjects were informed that the stimuli occurred inthat the picture wouldre(:ogniz:e the emotional

PYI"IPri-mPnt c e , o u J ~ e to a more phenomenologicaldefined criterion (cf. Cheesman & 1986).

In Experiment 3, the e:A'Po:mre time of the picture was he]d constantat 30 ms, and the target was exposed for 20 ms (in the lowest SOA and in the control


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all other As in 2, it was the SOA that wasbetween 20 and 300 ms. A control condition was also with

a neutral exJpm;ed for 20 ms followed a neutral mask. On each tria] thehad two tasks to np d 'n . -n was a or an angryto rate their confidence in that

Once again, the results showed an in the rates withand no above chance SOAs under 50 ms. The confidence data

showed that, when the SOAs were not moreconfident when choose theThus on these trials, even when correct answers were the """'i"'"t< " ' - ' ~ " ' " " ' "were guessing.

The comparison between the two dependent measures was ~ v u , . u p u ~ v . , : u - . ....the bias obtained in the control condition. When a neutral target wassubjects showed a bias to answer more often angry than alsocomplicated the comparison of and angry recognitions. if the controlcondition was used as the base rate, it was confirmed that it was easier tohappy expressions than angry, both on the forced-choice and on the confidence data.

Experiment 4 was a the same method that had beendeveloped in Experiment 3. In addition to the SOA used theexposure times of the target and the mask were also varied. It was observed that theSOA manipulation was the main factor influencing recognition, thus theincreased performance with longer SOAs obtained in the three previous experiments.Exposure time of the target and the mask showed

Two main conclusions can be drawn from this series of experiments. itwas shown that the SOA was the principal factor influencing of maskedfacial expressions. In an four of the emotional ofthe target with longer SOAs. Thus, it seems that rather than the exposuretime of the target per se (cf. Experiment it was the time available for ofthe target that was decisive. This the idea that the masking obtainedwas of central origin (cf. Turvey, In general, these ex]pex]m:ents indicated that aSOA of about 100 ms was necessary to accurately the facial ofthe target


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...,.,...,u.n.uy, and as a consequence of these rec:ognitionconduded that a SOA of 30 ms, which was the SOA used in the PV1riPr i , . , . ,in Studies II and did notof the there were individual . . . ~ ~ < ~ ' J ' = ~ , ~ it seems thata SOA of 30 ms was below threshold level of awareness for aUindependently ofwhich measure was used to assess rec:og1nition.2.4. THE CONDITIONING STUDIES2.4.1. The common method

The experiments reported :in Studies II and III were cases of aversivePavlovian conditioning manipulations. The conditioned stimuH as weB as themasking stimuli were of human facial expressions. The CSs could beor angry expressions and the masking stimuH were pictures of neutral ell.'])ressions.

The USs were m:ild electric shocks on the of the first and the secondfingers of the subjects'right hand. The intensity of the shock was adjusted individuallyfor each subject, to a level defined as "uncomfortable but not painful". The electricshocks were delivered through silver electrodes and consisted of 18 Hz current of 0.5seconds duration.

A differential conditioning paradigm was used. This consists of thecomparison between two equivalent stimuli, one of which is reinforced (the CS+ ), i.e.is presented together with the US, and another that is never reinforced (the CS-).This different treatment during the conditioning procedure (also called theacquisition phase), provided that responses to the stimu]i do not differ beforeconditioning, allows the of later differences in responding to beattributed to associative

The dependent variableElectrodermal

research for about one hundred years ScheU, & FiHion, The changesin the electric conductance of the human skin are attributed to theinnervation of the eccrine sweat which are exclusively controlled the


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29

also been used as a measure of unconscious activation

c) The three

there was ahabituationexperimental conditions, and to score the SCRs to the different stimuli before the

procedure to rule out initial response differences as a COJ1foundil11!!4-6 trials were exposed this phase.

The second phase was the conditioning phase, usually caned thephase. Here, one of the stimuli was foHowed by the shock US (the CS+ ), and anotherequivalent stimulus was presented nonreinforced (the CS-). In the experimentsreported in Study the CSs were not masked during the acquisition phase. Thus,although the exposure time was brief (60-200 ms), the acquisition phase wasnonmasked, and the subjects were given the opportunity to become aware of thepictures presented and which CS that was associated with the US. In the experimentsreported in Study III, the CSs were masked during the acquisition phase, e ither with ashort SOA (usually 30 ms), not allowing conscious :identification, or with a longerSOA (e. g., 180 ms), aHowing the subject to consciously perceive both the target andthe masking stimuli. Usually 12-16 trials for each CS were administered.

The concluding part of the experiments was the extinction phase. Here, theshock US was omitted and a series of CSs+ and CSs- was presented. In theexperiments reported in Study II, where a nonmasked acquisition had beenadministered, the CS:s were presented masked during el\.1::inction. The SOA usedcould be very short (30 ms), not aUowing a conscious of the CSs, orsomewhat longer (e. g., 180 ms ), aHowing the cm1scm1.1tslv discriminate

HI, where masked aCCIUIS:mcm had beenmong the different stimuli. Inthe extinction phase was nonmasked. Here, differential responding to the stimuli thathad been presented masked during acquisition could be attributed to associativelearning. Usually, this phase consisted of 16-20 trials for each CS.


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Phasic SCR amplitudes were scored as the maximal response ..,t


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In Experiment 1, two groups were compared. One group was conditioned toan angry facial expression (angry CS+) with a happy face serving as the controlstimulus, and the other one was conditioned to a happy facial expression (happyCS+) with an angry CS-. The experiment consisted of two phases - a habituationphase and a conditioning phase. The conditioning phase consisted of different trialconditions: (a) conditioning trials - 12 unmasked presentations of each CS, with theUS delivered 0.5 seconds after the onset of the CS+; (b) test-trials - threenonreinforced presentations of the unmasked CS+, which were compared to threeadjacent CS- trials in order to examine i f conditioning had occurred; (c) masked trials- six presentations of each CS, exposed for 30 ms and followed by a neutral maskingface also presented for 30 ms.

Although the exposure of the CSs was only 60 ms in the nonmasked trials, itwas sufficient to allow the subjects to become aware of which picture was shown oneach trial and, consequently, to figure out after some exposures which slide wasassociated with the shock and which was not. It was hypothesized that both groupswould show conditioning in the nonmasked test-trials, i.e., both groups would showlarger SCRs to the nonreinforced CS+ than to the correspondent CS-. Furthermore,it was expected that in the angry CS+, but not in the happy CS+ group, somedifferential responding between the CS + and the CS- would be obtained in themasked trials condition.

The analysis of the results showed the predicted conditioning effect in boththe angry CS+ and the happy CS+ groups, i.e., in the nonreinforced trials, subjectsin both groups responded more to the nonmasked CS+ than to the correspondingCS-. The differential effect found between the CS+ and the CS- in the masked trialswas, as expected, present only in the group conditioned to an angry expression and

... only on the first trials. Thus, some support was obtained for the hypothesis of~ ~ . - ~ c i t a t i o n physiological r e s p o ~ s e s masked stimuli. H ~ Y . e r h ! l w , , ~ l m ' f . t :Sl\ ~ ~ ~ L ~ - : ! : ~ tnal-bloc}::..lhe presentation of masked (and'nonremforced) trials interspersed among the conditioning trials could have resultedin the masking picture becoming an inhibitory stimulus, reducing the responding tothe CS+. Furthermore, stimulus changes from trial to trial could interfere withhabituation and result in increased electrodermal orienting responses (OR) thatcould complicate the interpretation of the conditioned responses. Thus inExperiment 2, acquisition and extinction phases were separated in order to allowhabituation to the masked CSs and to prevent inhibitory conditioning.


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2AI; the group conditioned to a

on the masked and the lack of differentiation extinctionobtained before with an angry group was run.in Experiment 2. It was to the angry CS+

to the happy CS- would be obtained in the masked extinction. In theresults replicated the effect obtained in 1. SCRs to themasked CS+ were reliably than responses to the masked CS-.

Taken together, the results of 1 and 2 :indicate that it is vu"''"'"''"to elicit responses to angry facial despite theinterruption of information-processing caused the backward masking. apreliminary stimulus analysis was sufficient to elicit SCRs under these conditions. Theinterference in the processing of the CSs prevented the subjects from becomingaware of the stimuli presented. However, whether this should be to meanthat the processing of the masked stimuli would be completely preattentive (as wouldbe suggested, e. g., Marcel, or i f some controlled prcJce;ssixig would takeplace (as suggested by Ohman, 1992) needed to be clarified.

A method that has been used to separate preattentive from controlled modesof information processing is to study the interference caused by a secondary task.Preattentive processing is usually defined as effortless, not requiring the aUocation ofcognitive resources, while interference caused by shared cognitive resources is takenas a central criterion of controlled processing. Thus in Experiment 3, a manipulationof attentional resources was used in order to study this issue.Experiment 3

Four groups with 12 subjects in each were studied. Two groups of subjectswere instructed to attend to the masking stimulus and count the number of femalesappearing in that position, while the other two groups had no attentional task.Furthermore, two SOA conditions were orthogonaHy combined with the two levels ofattention: one preattentive condition (30 ms and a condition that aHowed thesubject to consciously perceive the target CS ms In an four groups, theCS+ was an angry face and the CS- a happy one.


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It was expected that differential responding between the masked CS+ and themasked CS- would be obtained in the groups without the attentional task, both forthe group with 30 ms SOA (replicating Experiments 1 and 2) and for the group withthe longer SOA (cf. Ohman & Dimberg, 1978). It was also hypothesized that theattentional task would interfere with the physiological responding in the long SOAcondition, resulting in decreased differential responding. The last group, the one withshort SOA and attentional task, was indeed the most interesting one. Both decreaseddifferentiation between the CS+ and the CS- and no effect of the secondary taskcould be expected, depending on the level of processing interrupted by backwardmasking.

The results showed differential responding during extinction only in thegroups not given the attentional task. The two groups that had to pay attention to themask did not show any significant differentiation between the CS+ and the CS-.Thus, the fact that the attentional task eliminated the differential responding in the30 ms SOA group supports the hypothesis that some controlled processing waspossible even though the subjects had been prevented from becoming aware of themasked CSs (cf. Ohman, 1992a).

In summary, the three experiments showed that it is possible to elicitautonomic responses to masked conditioned stimuli when an angry face is used as theCS+. The results of Experiment 3 also suggest that although the subjects were notaware of the eliciting masked CSs, the processing involved is not completelypreattentive in the sense that some controlled processing seems to occur.2.4.3. Study i l l

Is associative learning in a context of Pavlovian conditioning possible when the CSsare masked and the subject is not aware of the CS-US relationship?

The general method used in these experiments can be said to be the oppositeto that used in Study II. While in Study II the conditioning procedure was nonmaskedand the extinction phase was masked, here it was the acquisition phase that wasmasked and the extinction phase nonmasked to test whether some associativelearning had occurred.

Study III consisted of two experiments and a pilot study. The pilot study canbe considered a complement to Study I. Because the recognition experiments (Study


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34

I) were conducted with no of and the conditioningexperiments (in both II and III) involved electric shock it isconceivable that differential responding to masked stimuli was a result of loweredrecognition thresholds because of US administration. The pilot wasconducted with ba:sicaHy the same method that had been used in I, Experiment3 above, p. The main difference was that ten at a level asuncomfortable but not painful the were delivered during theexperiment.

The results gave no indication that the thresholds had beenlowered by the shock exposure. Thus, the 30 ms SOA condition that was used beforecould be used again in Study III in order to the conscious of themasked CSs.Experiment 1

In Experiment 1, three groups with 20 subjects in each were compared. Onegroup was conditioned to an angry face, exposed for 30 ms and maskedface also exposed for 30 ms, with a masked happy face serving as the CS-. theextinction phase, the CS:s were exposed unmasked for 500 ms. This group, thePreattentive Conditioning Group, was compared to two control conditions. Onegroup was also conditioned to an angry face, exposed for 30 ms, with a happy face asthe CS-. Both CSs were foUowed masks exposed for 30 ms, but the SOA betweenthe target and the mask was extended to 330 ms. This group was the ConditioningControl Group. The extinction phase was identical to that of the Preattentive group.Another control group was conditioned to the masks, the Pseudo-conditioningControl Group. During acquisition, subjects were exposed to two neutral faces, onefollowed by a shock-US and the other serving as the CS-. During extinction they weretested in the same way as the subjects in the two other groups, i.e. they werepresented with a sequence of trials with a happy face or an angry face, exposed for500ms.

The theoretical notions behind the possibility of conditioning in thePreattentive group were somehow contradictory. If, as most authorsDawson & Furedy, 1976; Dawson & ScheU, 1985), awareness of the contingencybetween the CS and the US is a necessary condition for conditioning, then noconditioning effect should be expected. As the exposure conditions in this groupprevented the subjects from becoming aware of the the of awareness


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of the CS-US contingency was logicaHy excluded. On the other SCRs to angryfaces have survived backward masking after a procedure and,

the hypothesis of a special to detect angry faces Hansen & Hansen,there are theoretical reasons to expect a positive effect. Indeed, apreliminary experiment in our laboratory, although lac.ldng the necessary control

and therefore not reported, gave indications in that direction.

Conditioning group was the reason for the two control groups. In the case of anegative result, it was to show that a effect could have beenobtained if only the subjects became aware of the CSs. Thus, in the '-'"U"'"U'""'"'Control group, where the subjects were given the opportunity to become aware of theCScUS contingency, differential responding to the angry CS+ and the happy CS- wasexpected. This was important for interpreting possible negative results in thePreattentive Conditioning group. In the case of positive results in the PreattentiveConditioning group, the Pseudo-Conditioning group allowed the exclusion ofalternative explanations. For example, :in the preattent:ive group, differentialresponding to the angry and the happy faces during extinction could be attributed toa generalisation from the reinforced neutral mask to the angry face exposed duringextinction, without necessarily implying that the association between the maskedangry face and the shock-US had been learned. From the subject's point of view thiscontrol group was designed to be similar to the Preattentive group both cases onlythe neutral masks were consciously perceived). Thus, if differential responding wasobtained because of generalisation in the PreaUentive Conditioning group, then thecontrol group should also show a similar effect. Also, the possibility of a sensitizationeffect to the angry expression rather than to the happy one due to the shockpresentation could be ruled out by the same logic.

The results showed during the extinction phase, SCRs to the angry facewere larger and more frequent than to the happy face, both in the PreattentiveConditioning group and in the Conditioning Control group. The Pseudo-conditioningcontrol group showed no differentiation. Thus, Experiment 1 theof Pavlovian conditioning without the subjects being aware of the CS-US "'"'''".. F>""".JHowever, if this effect was specific to angry faces or if associative learning also couldbe obtained with, for example, happy faces, was stiH an open question. The purposeof Experiment 2 was to investigate the specificity issue, and replicate Experiment 1following some methodological improvements.


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Six groups with 20 subjects each were run. One group - Angry preattentive -was a replication of the Preattentive Conditioning group in Experiment 1, i.e. it wasan angry CS+ and a happy CS- both masked neutral faces with a SOA of 30ms. Furthermore, a Happy preattentive group was with a happy CS+ andan angry but was otherwise similar to the Angry Preattentive group. A thirdgroup was a of the Control group in 1, with alonger interval to further facilitate the perception of the CSsto a face with an angry face as the the Happy conditioning control group.The remaining groups were two sensitization control groups. During thesubjects in these groups were exposed to the same series of masked thatwere used in the conditioning groups and received the same number of shocks, butthese were delivered at random instead of being associated with one of the maskedfaces. One group had a 30 ms SOA and the other a SOA of 500 ms. During extinctionthe subjects in an the six groups were exposed to the same series of pictures.

It was expected that the two groups conditioned to angry faces would showdifferential responding during replicating the results of Experiment 1. Inthe two groups conditioned to happy faces, considering that conditioning to happyfaces in other experiments (e. g., Dimberg, 1986) did not show resistance toextinction, no effect was expected. Finally, no differentiation between the SCRs toangry and happy faces was expected in the sensitization control groups.

The results supported the hypothesis and replicated those results inExperiment 1. Only the two groups conditioned to angry facial expressions showeddifferential responding during extinction, i.e. subjects in these groups had larger andmore frequent SCRs to the angry CS+ compared to the happy CS-.

In summary, these two experiments showed that associative learning ispossible in conditions where the subjects are not aware of the contingencies ofreinforcement Furthermore, this effect appears to be restricted to some stimuluscategories, such as angry facial expressions.


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3. GENERAL DISCUSSION

3.1. UNCONSCIOUS PROCESSING OF ANGRY FACES

The main conclusion to be drawn from these studies is that angry facialto elicit physiological responses in a conte:Kt

the experiments reported in IIindicate that it is to elicit autonomic responses to conditioned angryeven when a backward masking presentation the from u ' - ' - n u w ' ~aware of the CSs. The IH showed that learning of anassociation between an aversive shock and an angry face did not theto be aware of the contingencies of reinforcement

One of the aims of Study I was to define conditions of stimulus exposureoutside of awareness. The results of the recognition experiments reported in Study Ishowed that, with the pictures of facial expressions that were used and with theiHumination conditions available, a mask exposed for 30 ms immediately foHowing atarget stimulus also exposed for 30 ms was sufficient to interfere with the processingof the target in a way that prevented the subject from becoming aware of it.Furthermore, this conclusion was confirmed by the result of the Pilot work reportedin Study HI. That is, the recognition thresholds did not seem to be affected shockstimulation. Thus, ahhough awareness was not assessed individuaHy in theexperiments reported in Studies II and III, it can be argued that the exposureconditions employed prevented the subjects from becoming aware of the targetpictures.

From Study I, three other condusions should be emphasized. First, the SOAseems to be the principal factor influencing the identification of the of thetarget. Thus, it was the increase of the SOA that facilitated recognition and not onlyexposure time of the target. This result is best integrated within anmodel of backward masking (Massaro, 1975), suggesting that the presentation of themasking stimulus interrupts the processing of the iconic representation of the target(Neisser, From an integration model perspective, where some kind of fusionbetween the target and the mask is postulated (e. g., BreHmeyer & Gan:z:, itwould be expected that the exposure time of the target should haveimportance. Furthermore, the of the SOA in the uw"'"'''u5characteristic of central masking (Turvey,

' " ' ' " ' " " " ~ ' " ' " " of central origin. Second, ,,.,..r,.,..,hour masking conditions were

parameters other than the SOA have


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little effect on the thresholds. This is an interesting result which' lH>nr r t ' the that the of. emotional expressions should be arobust phenomenon, even in cases of & JWA


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g., the teeth in athat this is just asense used Frijda

The results ofreported

39

and not unconscious emotional

that elicitation of SCRs to masked stimuH wasare in accordance with the results

and Soaresobtained a similar effect when snakes and " " " * " " " ' ' " ~ ' " ' of fear-relevant

were used as the CS+. The fact that , . . , , , l , hnn i rm faces did notu w ' ~ ' ' " " ' 5 should not be , , , r w i ~ i n

by -'-"' '"'"U 'v > to the resuhs withangry faces, did not show resistance to extinction

& thisfaces have an inhibitory effect on aversively

conditioned responses. Aliso other cases of conditioning with neutral CSs have faHedto show unconscious eliciting effects. Both Ferreira, and Ross (1974) usingletters as visual and and Soares (1993) with flowers and mushroomsas the showed that effective backward eliminated differentialresponding during extinction. Taken together, this obtained selectivity, thatonly f e a r ~ r e l e v a n t stimuli can resist masking and elicit conditioned responses,supports the preparedness

Although faces have failed to survive backward masking it must beadmitted that the possibility of a association between a US and ahappy face was not examined. Would it be possible to elicit responses to a maskedhappy face after a Pavlovian conditioning procedure using a US? Thisquestion, although important for the CS-US belongingness issue &Droungas, Ohman, 1993b), was not addressed in this thesis.

From the results of Experiment 3 in II attentional task was found tointerfere with physiological activation at a unconscious an importanttheoretical conclusion can be drawn. The elicitation of physiological responses is notcompletely automatic. Such a automaticity would imply no influence ofmanipulation in the direction of attention. u"''"""" it seems to be a case of

& Graham, 1991). A consequence of this result is theof human information p n J c ~ : : s s J n l ! :

(Ohman,


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integrate into the mainstream of the human Pavlovian literature. Ingeneral, awareness of the CS-US contingency is assumed to be necessary forcoJ10JtJo:nmg to occur (Dawson & Furthermore,has been denied in other contexts g.,

III showed that m r i . , , . t ~ that had beenconditioned to effectively masked angry faces showed differential respondingafterwards when to the CSs without masks. One ~ c - ~ u ~ " ' ' " ' " ' criticism of ourresults could be to question the effectiveness of backward uw"ru'"l';blockresults of Study I and the Pilot experiment in

ignoring thethat some

on some became aware of the masked and also could becomeaware of the CS-US contingency. the comparison with groups whichbecame aware of the CSs by (i.e., the conditioning control andtherefore also could became aware of the CS-US contingency, did not show anydifference. In fact, if awareness of the contingency of reinforcement was a necessarycondition for conditioning to occur, it should be expected that more subjects in theconditioning control groups, compared with the preattentive groups, would becomeconditioned. Thus, some differentiation should have been obtained between theseconditions, which was not the case.

This unconscious conditioning effect was obtained with fear-relevantstimuli (see also Ohman & Soares, Thus, a possible explanation of thediscrepancy between our results and the dominant perspective would be to admitthat, in general, awareness of the CS-US contingency is necessary for Pavlovianconditioning to occur, but when biologically relevant stimuli are used, partiallyautomatic stimulus analysis can take place and result in impHcit learning. Such acapacity of potential threatening stimuli to elicit brief attentional shifts (Ohman,

is in accordance with the "pop-out" effect described by Hansen and Hansen(1988).

is dependent on the definition of awareness and the choice of criteria for itsassessment. It should be emphasized that awareness of a perceived stimulus is not anali-or-none process. Some features of the target picture, by the attentional

could be integrated with the perception of the masking face (Breitmeyer &Ganz, what is important here is that the subjects were not aware ofhaving been exposed to the CSs. Thus, a more awareness criterion


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integration of the target and the mask deserves a last comment. In the controlconditions used in 2 and 3 neutral faces were usedas showed a tendency to more often the"'"'"'"''


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of an appropriated conscious appraisal

The importance of the detection of angry faces to social fear and phobiafollows from this approach. Although the political, economic and social structures ofthe existing societies have been the product of many transformations in the lastcenturies, social interactions at the level of the smaH group have not changed much.A reason for the actuality of the classic works in literature is this

Stories of love and hate are still regulated by the same mechanisms,whether they be called primitive or not. A correct of a person's emotionsand intentions an important role in our social interactions. Furthermore, thecorrect display and appraisal of facial expressions is related to the establishment ofdominance hierarchies, to the regulation of status within groups. Thus, earlydetection of facial threatening cues has a dear functional value. In given theimportance of faces in nonverbal communication it is plausible to admit that much ofour social interactions are influenced by unconscious appraisals of others facialdisplays. Furthermore, there is empirical evidence that this unconscious processingcan be self-perpetuating (Lewicki, Hill, & Sasaki, 1989). For example, negative firstimpressions could be confirmed by a biased decoding of emotional expressions.

This approach suggests that it is plausible that the unconscious processing ofaffective expressions plays a role in the development and maintenance of socialphobias and in anxiety disorders. Furthermore, the impairment of the ability of a

evaluation of others' emotional displays could be related to other dinicalproblems. The study of impairments in the recognition of emotional facialexpressions in schizophrenics is a recent but growing field (see Morrison, Bellack, &Mueser, 1988, for a review). Also, Cooley and Nowicki (1989) obtained slowerreaction times in the discrimination of emotional expressions in depressed patientscompared to normal subjects. Much work is still to be done in the understanding ofemotional behaviour and disturbances. The studies presented in this thesis are just asmall contribution to the field.


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