Simultaneous presentation of similar stimuli produces perceptual learning in human picture processing

Human participants received unsupervised exposure to difficult-to-discriminate stimuli (e.g., A and A'), created with a morphing procedure from photographs of faces, before learning a discrimination between them. Experiments 1 and 2 demonstrated that prior exposure enhanced later discrimination and that intermixed exposure (A, A', A, A'...) resulted in better subsequent discrimination than blocked exposure (B, B, ...B', B'...). Experiments 3 and 4 showed that simultaneous exposure to 2 similar stimuli facilitated the later acquisition of both a simultaneous and a successive discrimination, and this effect was observed even though simultaneous exposure to 2 stimuli fostered the development of an excitatory association between them (Experiment 5). The findings of Experiments 1 and 2 revealed a perceptual learning effect with pictures of faces, and the findings of Experiments 3-5 are difficult to reconcile with associative analyses of perceptual learning.     

Perceiving facial expressions

Three experiments investigated the perception of facial displays of emotions. Using a morphing technique, Experiment 1 (identification task) and Experiment 2 (ABX discrimination task) evaluated the merits of categorical and dimensional models of the representation of these stimuli. We argue that basic emotions—as they are usually defined verbally—do not correspond to primary perceptual categories emerging from the visual analysis of facial expressions. Instead, the results are compatible with the hypothesis that facial expressions are coded in a continuous anisotropic space structured by valence axes. Experiment 3 (identification task) introduces a new technique for generating chimeras to address the debate between feature-based and holistic models of the processing of facial expressions. Contrary to the pure holistic hypothesis, the results suggest that an independent assessment of discrimination features is possible, and may be sufficient for identifying expressions even when the global facial configuration is ambiguous. However, they also suggest that top-down processing may improve identification accuracy by assessing the coherence of local features.     

Categorization difficulty is associated with negative evaluation in the “uncanny valley” phenomenon

Human observers often experience strongly negative impressions of human‐like objects falling within a particular range of visual similarity to real humans (the “uncanny valley” phenomenon). We hypothesized that negative impressions in the uncanny valley phenomenon are related to a difficulty in object categorization. We produced stimulus images by morphing two of each of real, stuffed, and cartoon human face images (Experiment 1). Observers were asked to categorize each of these images as either category and evaluated the likability of the image. The results revealed that the longest latency, the highest ambiguity in categorization, and the lowest likability score co‐occurred at consistent morphing percentages. Similar results were obtained even when we employed stimulus images that were created by morphing two of each of real, stuffed, and cartoon dog images (Experiment 2). However, the effect of categorization difficulty on evaluation was weak when two real human faces were morphed (Experiment 3). These results suggest that the difficulty in categorizing an object as either of two dissimilar categories is linked to negative evaluation regardless of whether the object is human‐related or not.     

Perceptual learning and acquired face familiarity: Evidence from inversion,use of internal features,and generalization between viewpoints

Pairs of similar faces were created from photographs of different people using morphing software. The ability of participants to discriminate between novel pairs of faces and between those to which they had received brief, unsupervised, exposure (5×2 s each) was assessed. In all experiments exposure improved discrimination performance. Overall, discrimination was better when the faces were upright, but exposure produced improved discrimination for both upright and inverted faces (Experiment 1). The improvement produced by exposure was selective to internal face features (Experiment 2) and was evident when there was a change in orientation (three-quarter to full face or vice versa) between exposure and test (Experiment 3). These findings indicate that perceptual learning observed following brief exposure to faces exhibit well-established hallmarks of familiar face processing (i.e., internal feature advantage and insensitivity to a change of viewpoint). Considered in combination with previous studies using the same type of stimuli (Mundy, Honey, & Dwyer, 2007), the current results imply that general perceptual learning mechanisms contribute to the acquisition of face familiarity.     

Peak shift but not range effects in recognition of faces

University students were trained to discriminate between two gray-scale images of faces that varied along a continuum from a unique face to an average face created by morphing. Following training, participants were tested without feedback for their ability to recognize the positive face (S+) within a range of faces along the continuum. In Experiments 1 and 4, the range of stimuli presented during testing was manipulated. In Experiment 2, participants viewed different ranges of faces during an adaptation period that followed training and preceded testing. In all experiments, generalization functions revealed peak shifts or area shifts (fewer “yes” responses to novel faces on the negative side of the S+), but no systematic effects of the test or adaptation range. Peak shift was found both for upright and inverted faces and occurred even if the orientation of the face was reversed between training and test. Using similar methods, either an area shift or range effect (but not both together) was demonstrated for line tilt stimuli (Experiment 3), and the appearance of these effects depended on instructions. It appears that peak shift and area shift are robust across many different kinds of stimuli, but range effects may not readily occur with complex multidimensional stimuli.     

Categorization and Perceptual Learning: An Analogue of the Face Inversion Effect

This paper reports two experiments that investigate the extent to which it is plausible to suppose that an associatively based mechanism for perceptual learning acts as the basis for the effects of inversion on identification, recognition, matching and discrimination of faces (and certain other stimuli rendered familiar by expertise, e.g. gundogs). In the first experiment, an inversion effect that is contingent both on familiarity with a category and on the category possessing prototypical structure is demonstrated using discrimination learning of chequerboard stimuli. The second experiment demonstrates that the inversion effect found in Experiment 1 can generalize to a recognition paradigm as well. These results are discussed within the framework provided by associative learning theory, and a parallel is drawn with models employing a norm-based coding in similarity space. The conclusion is that it would be remarkable if the inversion effects demonstrated with the abstract categories used in the experiments reported here were not implicated in the inversion effects found with other classes of stimuli,whilstconceding thatthe analogy is notcomplete,particularly in the case of faces.     

知觉适应对种族融合面孔的种族分类和知觉辨别的影响

面孔加工的种族效应(the other-race effects)指人们对面孔做个体辨别任务时辨别本族面孔的绩效优于辨别他族面孔的绩效, 而做种族分类任务时分类他族面孔的绩效优于分类本族面孔的绩效。本研究通过知觉适应操纵被试对种族两歧(高加索和亚洲)融合面孔的种族知觉, 进而比较被试在两种条件下对同一张融合面孔进行种族分类和知觉辨别的绩效的差异。结果发现, 知觉适应能使被试产生将两歧融合面孔知觉为与原始面孔所属种族相反种族的知觉偏向, 并且, 伴随着这种知觉偏向, 两歧融合面孔的加工出现了他族分类优势和本族辨别优势, 提示社会认知因素对面孔加工的种族效应有重要作用。     

知觉经验对面孔整体加工的影响

基于经验的整体加工理论认为, 随着知觉经验的增多, 人们加工面孔的专家化能力逐渐增强。其中一种表现形式为, 在知觉面孔时更倾向于整体加工。该理论已经得到了一些实验证据的支持, 但未能解释另外一些研究的发现, 即对他族人群没有长期知觉经验的被试在加工他族面孔时也有强烈的整体加工。本研究旨在考察知觉经验对面孔整体加工的影响, 包括两个实验。实验1a通过组合面孔范式测量了中国被试在辨别本族面孔、他族面孔和种族融合面孔时的组合面孔效应(即面孔整体加工强度)。结果发现, 被试在知觉种族融合面孔时没有表现出组合面孔效应, 在知觉本族面孔和他族面孔时都表现出强烈的组合面孔效应。实验1b以灰阶图重复了实验1a。结果发现, 被试在知觉种族融合面孔时仍然没有表现出组合面孔效应, 在知觉本族面孔和他族面孔时表现出强烈的组合面孔效应。实验2通过操纵种族融合面孔的有或无, 测量5 s的知觉经验对融合面孔的组合效应的影响。结果发现, 在经过短时的知觉经验后, 被试在知觉融合面孔时也表现出强烈的组合面孔效应。上述实验结果表明, 中国被试在加工本族面孔、他族面孔和种族融合面孔时所诱发组合面孔效应有显著的、量的差别, 且这种整体加工的差异不会受到面孔肤色信息的影响。在经过短时的知觉经验后, 中国被试在加工种族融合面孔时表现出强烈的整体加工。该研究的发现提示, 不论是短时知觉经验还是长期知觉经验, 知觉经验的增加是面孔整体加工的一个关键要素。     

Infant discrimination of faces in naturalistic events: actions are more salient than faces

Despite the fact that faces are typically seen in the context of dynamic events, there is little research on infants' perception of moving faces. L. E. Bahrick, L. J. Gogate, and I. Ruiz (2002) demonstrated that 5-month-old infants discriminate and remember repetitive actions but not the faces of the women performing the actions. The present research tested an attentional salience explanation for these findings: that dynamic faces are discriminable to infants, but more salient actions compete for attention. Results demonstrated that 5-month-old infants discriminated faces in the context of actions when they had longer familiarization time (Experiment 1) and following habituation to a single person performing 3 different activities (Experiment 2). Further, 7-month-old infants who have had more experience with social events also discriminated faces in the context of actions. Overall, however, discrimination of actions was more robust and occurred earlier in processing time than discrimination of dynamic faces. These findings support an attentional salience hypothesis and indicate that faces are not special in the context of actions in early infancy.     

A perceptual discrimination investigation of the own‐race effect and intergroup experience

Research over the past two decades has demonstrated that individuals are better at the recognition and discrimination of own‐ versus other‐race faces. Recent evidence, however, supports an own‐race effect at the level of perceptual encoding in adults. The current study examines the perceptual basis of the own‐race effect in secondary students from two racially segregated communities (White and South Asian). The contact hypothesis is investigated, as other‐race experience may influence other‐race face perception. Face stimuli were generated by morphing together South Asian and White faces along a linear continuum. In a same/different perceptual discrimination task participants judged whether face stimuli were physically identical to, or different from, the original faces. Results revealed a significant own‐race effect for the White participants only, wherein they were better at discriminating White relative to South Asian faces. Other‐race individuating experience was found to predict the own‐race effect, indicating that other‐race experience influences other‐race face perceptual expertise. Copyright © 2006 John Wiley & Sons, Ltd.     

Categorical perception of affective and linguistic facial expressions

Two experiments investigated categorical perception (CP) effects for affective facial expressions and linguistic facial expressions from American Sign Language (ASL) for Deaf native signers and hearing non-signers. Facial expressions were presented in isolation (Experiment 1) or in an ASL verb context (Experiment 2). Participants performed ABX discrimination and identification tasks on morphed affective and linguistic facial expression continua. The continua were created by morphing end-point photo exemplars into 11 images, changing linearly from one expression to another in equal steps. For both affective and linguistic expressions, hearing non-signers exhibited better discrimination across category boundaries than within categories for both experiments, thus replicating previous results with affective expressions and demonstrating CP effects for non-canonical facial expressions. Deaf signers, however, showed significant CP effects only for linguistic facial expressions. Subsequent analyses indicated that order of presentation influenced signers’ response time performance for affective facial expressions: viewing linguistic facial expressions first slowed response time for affective facial expressions. We conclude that CP effects for affective facial expressions can be influenced by language experience.     

Sensitivity to spacing changes in faces and nonface objects in preschool-aged children and adults

Sensitivity to variations in the spacing of features in faces and a class of nonface objects (i.e., frontal images of cars) was tested in 3- and 4-year-old children and adults using a delayed or simultaneous two-alternative forced choice matching-to-sample task. In the adults, detection of spacing information was robust against exemplar differences for faces but varied across exemplars for cars (Experiment 1A). The 4-year-olds performed above chance in both face and car discrimination even when differences in spacing were very small (within ±1.6 standard deviations [SDs]) and the task involved memory components (Experiment 1B), and the same was true for the 3-year-olds when tested with larger spacing changes (within ±2.5 SDs) in a task that posed no memory demands (Experiment 2). An advantage in the discrimination of faces over cars was found at 4 years of age, but only when spacing cues were made more readily available (within ±2.5 SDs). Results demonstrate that the ability to discriminate objects based on feature spacing (i.e., sensitivity to second-order information) is present at 3 years of age and becomes more pronounced for faces than cars by 4 years of age.     

A developmental investigation of other‐race contact and the own‐race face effect

Research over the past two decades has demonstrated that individuals are better at recognizing and discriminating faces of their own race versus other races. The own‐race effect has typically been investigated in relation to recognition memory; however, some evidence supports an own‐race effect at the level of perceptual encoding in adults. The current study investigated the developmental basis of the own‐race effect in White primary students (aged 7–11), secondary students (aged 12–15) and university students. Face stimuli were generated by morphing South Asian and White parent faces together along a linear continuum. In a same/different perceptual discrimination task, participants judged whether the face stimuli (morphs and parent faces) were physically identical to or different from the original parent faces. Results revealed a significant race of face effect for each age group, whereby participants were better at discriminating White relative to Asian faces. A significantly larger own‐race effect was observed for the secondary and university students than for primary students. A questionnaire was used to assess other‐race social anxiety and contact; however, this self‐report measure was not found to be related to the observed own‐race effect.     

Categorization,categorical perception,and asymmetry in infants’ representation of face race

The present study examined whether 6‐ and 9‐month‐old Caucasian infants could categorize faces according to race. In Experiment 1, infants were familiarized with different female faces from a common ethnic background (i.e. either Caucasian or Asian) and then tested with female faces from a novel race category. Nine‐month‐olds were able to form discrete categories of Caucasian and Asian faces. However, 6‐month‐olds did not form discrete categories of faces based on race. In Experiment 2, a second group of 6‐ and 9‐month‐olds was tested to determine whether they could discriminate between different faces from the same race category. Results showed that both age groups could only discriminate between different faces from the own‐race category of Caucasian faces. The findings of the two experiments taken together suggest that 9‐month‐olds formed a category of Caucasian faces that are further differentiated at the individual level. In contrast, although they could form a category of Asian faces, they could not discriminate between such other‐race faces. This asymmetry in category formation at 9 months (i.e. categorization of own‐race faces vs. categorical perception of other‐race faces) suggests that differential experience with own‐ and other‐race faces plays an important role in infants’ acquisition of face processing abilities.     

Memorization and “feature selection” in the acquisition of natural concepts in pigeons

Pigeons were trained on a successive discrimination task using complex visual stimuli. In Experiment 1, each photographic slide that contained a person had a corresponding “matched background” slide, one that showed the same scene with the person removed. Birds trained on a human positive discrimination acquired the matched pairs problem, but birds trained on a human negative discrimination performed poorly. This suggests a feature-positive effect for complex stimulus categories. Memorization control groups that were trained on a human-irrelevant discrimination also performed poorly with matched slides. However, subsequent experiments demonstrated that these effects depended on the use of matched pairs of slides. The human-as-feature effect was not obtained when human positive and human negative groups were subsequently trained with non-matched slides (Experiment 2), and memorization control groups acquired a human-irrelevant discrimination when trained with nonmatched slides (Experiment 3). Additional tests conducted in Experiments 2 and 3 found that performance was not disrupted when either the reinforced or nonreinforced slides were replaced. This effect was obtained when the category was relevant to the discrimination (Experiment 2) and when the category was irrelevant to the discrimination (Experiment 3). Finally, Experiment 4 demonstrated that memorization of a set of slides is possible when slides are sufficiently dissimilar, (i.e., nonmatched) but performance is not as good when the category exemplars are irrelevant to the discrimination.     

Semantic interpretation effects on memory for faces

Five experiments investigated the effects of semantically interpreting faces on their recognition. Experiment 1 demonstrated that faces could meaningfully be related to occupational categories. In Experiments 2–5, each of a set of faces was presented with either the label of a congruent occupational category or a noncongruent label. Presenting a face with a congruent occupational label was found to enhance recognition that the face had previously been seen (Experiments 2–4), but congruent labeling also impaired the detection of distractor faces that matched previously seen faces’ categories (Experiments 3 and 4). In a forced-choice recognition test, in which distractors were highly similar to originally seen faces, congruent occupational labeling failed to increase recognition of previously seen faces (Experiment 5). These results indicate that interpreting faces, with respect to stereotyped categories, ratherthan improving a physical codein memory, led to theformation of a semantic code, which increased recognition of old items at the expense of the detection of new items. Another general finding was that faces that were rated more stereotypical were more recognizable, regardless of the accompanying label.     

Conscious and nonconscious discrimination of facial expressions

Abrupt discontinuities in recognizing categories of emotion are found for the labelling of consciously perceived facial expressions. This has been taken to imply that, at a conscious level, we perceive facial expressions categorically. We investigated whether the abrupt discontinuities found in categorization for conscious recognition would be replaced by a graded transition for subthreshold stimuli. Fifteen volunteers participated in two experiments, in which participants viewed faces morphed from 100% fear to 100% disgust along seven increments. In Experiment A, target faces were presented for 30 ms, in Experiment B for 170 ms. Participants made two-alternative forced-choice decisions between fear and disgust. Results for the 30 ms presentation time indicated a significant linear trend between degree of morphing and classification of the images. Results for 170 ms presentation time followed the higher order function found in studies of categorical perception. These results provide preliminary evidence for separate processes underlying conscious and nonconscious perception of facial expressions of emotion.     

Effects of geometric distortions,Gaussian blur,and contrast negation on recognition of familiar faces

It is assumed that “configural processing” is important for recognizing people whom we know. Studies have shown better discrimination of relational changes between facial features when faces are presented upright than upside down and when presented as photographic negatives. However, studies have also demonstrated tolerance for complex changes to facial configuration of familiar faces when images are geometrically distorted. In two experiments, we explored effects of linear stretching, Gaussian blur, and contrast negation on recognition of familiar or unfamiliar faces (Experiment 1) and familiar or unfamiliar company brand logos (Experiment 2). Only contrast negation severely impaired recognition of familiar faces but not unfamiliar faces or company brand logos. Effects of contrast negation were additional to linear stretching, whereas linear stretching independently had no impact on recognition. These findings highlight an important deficit in the recognition of familiar faces caused by contrast negation.     

Evaluative conditioning depends on higher order encoding processes

Evaluative conditioning (EC) is commonly conceived as stimulus-driven associative learning. Here, we show that internally generated encoding activities mediate EC effects: Neutral conditioned stimuli (CS) faces were paired with positive and negative unconditioned stimuli (US) faces. Depending on the encoding task (Is CS a friend vs. enemy of US?), Experiment 1 yielded either normal EC effects (CS adopting US valence) or a reversal. This pattern was conditional on the degree to which encoding judgements affirmed friend or enemy encoding schemes. Experiments 2a and 2b replicated these findings with more clearly valenced US faces and controlling for demand effects. Experiment 3 demonstrated unconditional encoding effects when participants generated friend or enemy relations between CS and US faces. Explicitly stated friend or enemy relations in Experiment 4 left EC effects unaffected. Together, these findings testify to the importance of higher order cognitive processes in conditioning, much in line with recent evidence on the crucial role of conditioning awareness.     

Line‐up Misidentifications: When Being ‘Prototypically Black’ is Perceived as Criminal

Eyewitness misidentifications are the leading factor contributing to wrongful convictions. Black men, more than any other racial group, are disproportionately affected by this, thus elevating the importance of identifying factors that contribute to the false recollection of unseen faces. In the current studies, we tested whether misplaced familiarity and subsequent misidentification of Black faces was underpinned by the degree to which target faces were considered ‘prototypical’ (i.e., representative) of the Black race category. First, results revealed that Black faces with stereotypical facial features were accurately categorized as ‘Black’ quicker than faces with nonstereotypical features (Experiment 1). Moreover, identification errors were higher for both face recognition (Experiment 2) and line‐up identification (Experiment3) for stereotypical‐featured than nonstereotypical‐featured faces. Overall, results suggest that stereotypical Black faces are representative of the category ‘Black’ and facilitated feelings of familiarity and the endorsement of memory errors that may underpin eyewitness misidentifications. Copyright © 2013 John Wiley & Sons, Ltd.