Early experience is associated with the developmentof categorical representations for facialexpressions of emotionSeth D. Pollak*†‡and Doris J. Kistler‡*Department of Psychology and‡Waisman Center, University of Wisconsin, Madison, WI 53706Edited by Michael I. Posner, University of Oregon, Eugene, OR, and approved May 13, 2002 (received for review March 21, 2002)A fundamental issue in human development concerns how theyoung infant’s ability to recognize emotional signals is acquiredthrough both biological programming and learning factors. Thisissue is extremely difficult to investigate because of the variety ofsensory experiences to which humans are exposed immediatelyafter birth. We examined the effects of emotional experience onemotion recognition by studying abused children, whose experi-ences violated cultural standards of care. We found that theaberrant social experience of abuse was associated with a changein children’s perceptual preferences and also altered the discrimi-native abilities that influence how children categorize angry facialexpressions. This study suggests that affective experiences caninfluence perceptual representations of basic emotions.Categorization is an adaptive feature of perception and cog-nition that allows us to respond quickly and appropriately tofeatures of our environment. Social signals, such as thoseconveyed by the face, have long been regarded as important cuesfrom the environment that require immediate and accuraterecognition (1), yet we know little about the mechanisms throughwhich humans form perceptual categories of emotion. Thephenomenon of ‘‘categorical perception’’ may help us to under-stand more about the ontogenesis of emotional categories.Categorical perception effects occur when some kind of percep-tual mechanism enhances our perception of differences betweencategories, at the expense of our perception of incrementalchanges in the stimulus within a category. Perceiving in terms ofcategories allows an observer to efficiently assess changes be-tween categories (to see that a traffic light has changed fromgreen to yellow) at the cost of noticing subtle changes in astimulus (such as shades of greens or yellows across individualtraffic lights). Here we show that human perceptual categoriesfor basic emotions appear to be different among a group ofchildren that have had social experiences that violate culturalstandards of care. Children who experienced extreme physicalharm from their parents showed alterations in their perceptualcategories for anger as compared with nonabused children. Yet,abused children identified and discriminated other emotions inthe same manner as nonabused children. This finding bothaddresses central issues about the developmental processesthrough which humans learn to perceive emotion expressionsand also sheds light on the factors that put maltreated childrenat risk for behavioral pathology.The earliest demonstrations of categorical perception in thearea of speech perception stressed the importance of specializedinnate mechanisms (2, 3). However, later investigations haverevealed that perceptual capacities for speech, as well as otherperceptual domains, are not determined by maturational pro-cesses independent of experience (4–7). Rather, it appears thatalthough human infants may enter the world with perceptualcapacities that allow them to conduct a preliminary analysis oftheir environments, they need to adjust or tune these mecha-nisms to process specific aspects of their environment (8, 9).Categorical perception of facial expressions of emotions hasbeen demonstrated in adults (10–12). These studies have foundthat although participants are presented with instances of facialexpressions distributed along a continuum between emotions(e.g., happiness to sadness), observers perceive these stimuli asbelonging to discrete categories (happiness or sadness). Studieshave demonstrated that category boundaries for familiar andunfamiliar faces can be shifted in adults as a function offrequency of exposure to those faces (13). This feature ofperceptual processing of faces is associated with frequencyof exposure in adults, suggesting that experience may also playan important role in face perception. However, testing the effectsof familiarity with classes of emotional expressions is consider-ably more difficult than assessing recognition of individual faces.This is because it is difficult to measure the frequency of adeveloping child’s exposure to facial displays of emotion, ashuman children are always exposed to complicated affectiveexperiences from birth. Not surprisingly, people are very skilledat understanding each other’s facial expressions and appear todevelop this expertise at an early age (14, 15). The presentexperiment sought to identify experiential effects in humanrecognition of facial displays of affect.Because it is difficult to empirically measure the parameters ofan individual’s prior knowledge of, and experience with, basicemotion signals, we examined the perception of emotion inseverely abused children. We reasoned that abused childrenwould have had prior experiences with the communication ofemotion that differed in important ways from nonabused chil-dren. The emotional environments of these children includeperturbations in both the frequency and content of their emo-tional interactions with their caregivers (16, 17). Children whowere physically abused by their parents and nonabused controls(matched on age and IQ to the maltreated children) performeda facial discrimination task that required them to distinguishfaces that had been morphed to produce a continuum on whicheach face differed in signal intensity. To create continua of facialexpressions of affect, we used a two-dimensional morphingsystem to generate stimuli that spanned four emotional catego-ries: happiness, anger, fear, and sadness (Fig. 1). After thediscrimination task, children completed an identification taskwith each facial image used in the previous discrimination task.MethodsSubjects. Forty children (mean age ⫽ 9 years, 3 months), 22 malesand 18 females, participated in these studies. Seventeen non-abused children were recruited from a local after-school pro-gram and 23 physically abused children were recruited from astate psychiatric facility and a local social welfare agency servingmaltreated children. Abuse histories (or lack thereof) wereverified based on reviews of clinical and legal records. Allparticipants
View Full Document
Unlocking...