Perceptual expertise enhances the resolution but not the number of representations in working memory

Despite its central role in cognition, capacity in visual working memory is restricted to about three or four items. Curby and Gauthier (2007) examined whether perceptual expertise can help to overcome this limit by enabling more efficient coding of visual information. In line with this, they observed higher capacity estimates for upright than for inverted faces, suggesting that perceptual expertise enhances visual working memory. In the present work, we examined whether the improved capacity estimates for upright faces indicates an increased number of "slots" in working memory, or improved resolution within the existing slots. Our results suggest that perceptual expertise enhances the resolution but not the number of representations that can be held in working memory. These results clarify the effects of perceptual expertise in working memory and support recent suggestions that number and resolution represent distinct facets of working memory ability.     

A computer-generated face database with ratings on realism, masculinity, race, and stereotypy

Ratings of realism, masculinity, race, and racial stereotypy were collected on a set of computer-generated faces representing European, South East Asian, and African American ethnicities. To determine if these faces are processed in the same way as photographs of real faces, we demonstrated with these faces superior memory performance for upright faces over inverted faces (the face inversion effect). Further, in observers of European decent, we found both superior memory for European faces and a larger inversion effect for European than African American faces. Based on these results, we believe that this set of faces may be of use in perceptual investigations in which race is a critical manipulation.     

Discrimination of faces and houses by rhesus monkeys: the role of stimulus expertise and rotation angle

The face inversion effect, or impaired recognition of upside down compared to upright faces, is used as a marker for the configural processing of faces in primates. The inversion effect in humans and chimpanzees is strongest for categories of stimuli for which subjects have considerable expertise, primarily conspecifics’ faces. Moreover, discrimination performance decreases linearly as faces are incrementally rotated from upright to inverted. This suggests that rotated faces must be transformed, or normalized back into their most typical viewpoint before configural processing can ensue, and the greater the required normalization, the greater the likelihood of errors resulting. Previous studies in our lab have demonstrated a general face inversion effect in rhesus monkeys that was not influenced by expertise. Therefore, the present study examined the influence of rotation angle on the visual perception of face and nonface stimuli that varied in their level of expertise to further delineate the processes underlying the inversion effect in rhesus monkeys. Five subjects discriminated images in five orientation angles. Results showed significant linear impairments for all stimulus categories, including houses. However, compared to the upright images, only rhesus faces resulted in worse performance at rotation angles greater than 45°, suggesting stronger configural processing for stimuli for which subjects had the greatest expertise.     

The perception of unfamiliar faces and houses by chimpanzees: influence of rotation angle

The inversion effect, or impaired recognition of upside-down faces, is used as evidence supporting the configural processing of faces. Human studies report a linear relationship between face-discrimination performance and orientation, such that recognition is more difficult as faces are rotated away from their typical viewpoint. Previous studies on chimpanzees also support a configural bias for processing faces, particularly faces for which subjects have developed expertise. In the present study, we examined the influence of expertise and rotation angle on the visual perception of faces in chimpanzees. Six subjects were presented with unaltered and blurred conspecific faces and houses in five orientation angles. A computerized paradigm was used to further delineate the nature of configural face processing in this species. The data were consistent with those reported in humans: chimpanzees showed a significant linear impairment when discriminating conspecific faces as they rotated away from their upright orientation. No inversion effect was observed for discriminations involving houses. Thus, chimpanzees, like humans, show a face-specific inversion effect that is linearly affected by angle of orientation, suggesting that their visual processing of faces is strongly influenced by the extraction of configural cues and closely resembles the perceptual strategies of humans.     

A visual short-term memory advantage for faces

What determines how much can be stored in visual short-term memory (VSTM)? Studies of VSTM have focused largely on stimulus-based properties such as the number or complexity of the items stored. Recent work also suggests that capacity is severely reduced for items within the same category. However, the importance for VSTM capacity of more qualitative differences in processing for different categories has not been investigated. For example, faces are processed more holistically than other objects. In Experiments 1 and 2, we show that the processing of faces, objects that are crucial socially and for which we possess considerable expertise, overcomes these limitations. More faces can be stored in VSTM than objects from other complex nonface categories. As in prior studies, at short encoding durations we found that capacity for faces was less than that for other categories. However, at longer encoding durations, capacity for faces exceeded that for nonface objects, and this advantage was specific to upright faces. Because inversion reduces holistic processing, the interaction of orientation with VSTM capacity—which occurred for faces but not objects in Experiment 3—suggests that it is holistic processing that confers an advantage for face VSTM when sufficient encoding time is allowed.     

The other-race effect does not rely on memory: Evidence from a matching task

Viewers are typically better at remembering faces from their own race than from other races; however, it is not yet established whether this effect is due to memorial or perceptual processes. In this study, UK and Egyptian viewers were given a simultaneous face-matching task, in which the target faces were presented upright or upside down. As with previous research using face memory tasks, participants were worse at matching other-race faces than own-race faces and showed a stronger face inversion effect for own-race faces. However, subjects' performance on own and other-race faces was highly correlated. These data provide strong evidence that difficulty in perceptual encoding of unfamiliar faces contributes substantially to the other-race effect and that accounts based entirely on memory cannot capture the full data. Implications for forensic settings are also discussed.     

本族和异族面孔的视觉工作记忆容量:面孔特征的影响

采用延迟探测刺激匹配再认任务,考察面孔种族和内外部特征是否会影响面孔视觉工作记忆容量。被试先识记2或4张中国人或白人的真实面孔图片,一半有内部特征(眼睛、鼻子和嘴巴),另一半有内部和外部特征(脸型、发型),再进行面孔再认判断。采用Cowan’s K值的分析显示,我国被试对本族和异族面孔的视觉工作记忆容量没有差异,但面孔数量与特征多少会影响面孔工作记忆容量,表明对本族和异族面孔的视觉加工不同。     

Familiarity enhances visual working memory for faces

Although it is intuitive that familiarity with complex visual objects should aid their preservation in visual working memory (WM), empirical evidence for this is lacking. This study used a conventional change-detection procedure to assess visual WM for unfamiliar and famous faces in healthy adults. Across experiments, faces were upright or inverted and a low- or high-load concurrent verbal WM task was administered to suppress contribution from verbal WM. Even with a high verbal memory load, visual WM performance was significantly better and capacity estimated as significantly greater for famous versus unfamiliar faces. Face inversion abolished this effect. Thus, neither strategic, explicit support from verbal WM nor low-level feature processing easily accounts for the observed benefit of high familiarity for visual WM. These results demonstrate that storage of items in visual WM can be enhanced if robust visual representations of them already exist in long-term memory.     

Face processing skills predict faithfulness of portraits drawn by novices

Individuals show astonishing variability in their face recognition abilities, and the causes and consequences of this heterogeneity are unclear. Special expertise with faces, for example in portraitists, is associated with advantages on face processing tasks, especially those involving perceptual abilities. Do face processing skills improve through practice, or does drawing skill reflect pre-existing individual differences? If the latter, then the association between face processing skills and production of faithful portraits should also exist in people without practice in drawing. Two exploratory studies and one follow-up confirmatory study provide support for this hypothesis. Drawing ability of novices was predicted by their performance on face recognition tasks involving perceptual discrimination and visual short-term memory, but not by those that rely more heavily on long-term memory or memory for non-face objects. By examining non-experts, we show that expertise with faces might build upon pre-existing individual differences in face processing skills.     

The effect of face inversion on the detection of emotional faces in visual search

Past literature has indicated that face inversion either attenuates emotion detection advantages in visual search, implying that detection of emotional expressions requires holistic face processing, or has no effect, implying that expression detection is feature based. Across six experiments that utilised different task designs, ranging from simple (single poser, single set size) to complex (multiple posers, multiple set sizes), and stimuli drawn from different databases, significant emotion detection advantages were found for both upright and inverted faces. Consistent with past research, the nature of the expression detection advantage, anger superiority (Experiments 1, 2 and 6) or happiness superiority (Experiments 3, 4 and 5), differed across stimulus sets. However both patterns were evident for upright and inverted faces. These results indicate that face inversion does not interfere with visual search for emotional expressions, and suggest that expression detection in visual search may rely on feature-based mechanisms.     

The cost of facing fear: Visual working memory is impaired for faces expressing fear

Previous research has identified numerous factors affecting the capacity and accuracy of visual working memory (VWM). One potentially important factor is the emotionality of the stimuli to be encoded and held in VWM. We often must hold in VWM information that is emotionally charged, but much is still unknown about how the emotionality of stimuli impacts VWM performance. In the current research, we performed four studies examining the impact of fearful facial expressions on VWM for faces. Fearful expressions were found to produce a consistent cost to VWM performance. This cost was modulated by encoding time, but not set size. This cost was only present for faces in an upright orientation consistent with this cost being a product of the emotionality of the faces rather than lower‐level perceptual differences between neutral and fearful faces. These findings are discussed in the context of existing theoretical accounts of the impact of emotion on information processing. We suggest that a number of competing effects drive both costs and benefits and are at play when emotional information must be stored in VWM, with the task context determining the balance between them.     

The other-race effect does not rely on memory: Evidence from a matching task

Viewers are typically better at remembering faces from their own race than from other races; however, it is not yet established whether this effect is due to memorial or perceptual processes. In this study, UK and Egyptian viewers were given a simultaneous face-matching task, in which the target faces were presented upright or upside down. As with previous research using face memory tasks, participants were worse at matching other-race faces than own-race faces and showed a stronger face inversion effect for own-race faces. However, subjects' performance on own and other-race faces was highly correlated. These data provide strong evidence that difficulty in perceptual encoding of unfamiliar faces contributes substantially to the other-race effect and that accounts based entirely on memory cannot capture the full data. Implications for forensic settings are also discussed.     

Visual working memory capacity for objects from different categories: a face-specific maintenance effect

The capacity of visual working memory was examined when complex objects from different categories were remembered. Previous studies have not examined how visual similarity affects object memory, though it has long been known that similar-sounding phonological information interferes with rehearsal in auditory working memory. Here, experiments required memory for two or four objects. Memory capacity was compared between remembering four objects from a single object category to remembering four objects from two different categories. Two-category sets led to increased memory capacity only when upright faces were included. Capacity for face-only sets never exceeded their nonface counterparts, and the advantage for two-category sets when faces were one of the categories disappeared when inverted faces were used. These results suggest that two-category sets which include faces are advantaged in working memory but that faces alone do not lead to a memory capacity advantage.     

On facial expertise: processing strategies of twins' parents

Parents of monozygotic twins typically learn to recognise their own children and also to tell them apart on photographs. However, it is unknown whether such exemplar expertise can be generalised to unfamiliar faces of equal similarity (ie other twins). In the present study, parents of monozygotic twins were compared to 'control' parents whose children were non-twin siblings. In a same/different task with familiar and unfamiliar twin faces as stimuli, twins' parents were faster than control parents in distinguishing their own children, but slower when distinguishing unfamiliar twin faces. These unexpected findings can be interpreted as a generalisation of a habitual perceptual strategy that is efficient only with familiar face exemplars. When pictures of the twins' faces were inverted by 180degrees, the typical inversion costs for familiar faces were observed, but the twins' parents recognised unfamiliar twins' faces better when these were inverted than when upright. This inverted inversion effect could be caused by the high similarity of the face pairs as well as by experience with familiar faces of equally high similarity. We conclude that the facial expertise of twins' parents is idiosyncratic to their own children and not based on an enhanced general facial expertise.     

Information processing during face recognition: the effects of familiarity, inversion, and morphing on scanning fixations

Where we make ocular fixations when viewing an object likely reflects interactions between 'external' object properties and internal 'top-down' factors, as our perceptual system tests hypotheses and attempts to make decisions about our environment. These scanning fixation patterns can tell us how and where the visual system gathers information critical to specific tasks. We determined the effects of the internal factors of expertise, experience, and ambiguity on scanning during a face-recognition task, in eight subjects. To assess the effects of expertise, we compared upright with inverted faces, since it is hypothesized that inverted faces do not access an orientation-dependent face-expert processor. To assess the effects of experience, we compared famous with novel faces, as famous faces would have stronger internal representations than anonymous ones. Ambiguity in matching seen and remembered faces was manipulated with morphed faces. We measured three classes of variables: (i) total scanning time and fixations; (ii) the spatial distribution of scanning; and (iii) the sequence of scanning, using first-order Markov matrices for local scan structure and string editing for global scan structure. We found that, with inverted faces, subjects redistributed fixations to the mouth and lower face, and their local and global scan structure became more random. With novel or morphed faces, they scanned the eyes and upper face more. Local scan structure was not affected by familiarity, but global scan structure was least random (most stereotyped) for novel upright faces. We conclude that expertise (upright faces) leads to less lower-face scanning and more predictable global patterns of information gathering. Experience (famous faces) leads to less upper-face scanning and more idiosyncratic global scan structures, suggesting a superseding influence of facial memories. With morphed faces, subjects return to the upper face to resolve ambiguity, implying a greater importance of this region in face recognition.     

Face inversion and contrast-reversal effects across development: in contrast to the expertise theory

To determine the role of configural changes on the development of face encoding and memory, we investigated face recognition in an n-back repetition task with upright, inverted and contrast-reversed unfamiliar faces in adults and children (8-16 years). Repetitions occurred immediately (0-lag) or after one intervening face (1-lag). Face recognition continued to develop beyond 14-16 years, as shown with hit rates, d' scores and reaction times that all improved with age. Inversion and contrast-reversal effects were found in all subjects but were not more pronounced with increasing age, suggesting no increased reliance on configural processing and thus arguing against the expertise theory of Diamond and Carey (1986). Recognition improved with age in upright but also in inverted and contrast-reversed faces, suggesting a quantitative rather than a qualitative developmental change in face processing. For all age groups, performances decreased and reaction times increased from 0- to 1-lag conditions similarly, suggesting a similar memory component involved in adults' and children's processing. These data suggest gradual quantitative improvements in face processing with age, mainly due to increasing working memory processing capacity.     

An inversion effect modified by expertise in capuchin monkeys

The face inversion effect may be defined as the general impairment in recognition that occurs when faces are rotated 180°. This phenomenon seems particularly strong for faces as opposed to other objects and is often used as a marker of a specialized face-processing mechanism. Four brown capuchin monkeys (Cebus apella) were tested on their ability to discriminate several classes of facial and non-facial stimuli presented in both their upright and inverted orientations in an oddity task. Results revealed significantly better performance on upright than inverted presentations of capuchin and human face stimuli, but not on chimpanzee faces or automobiles. These data support previous studies in humans and other primates suggesting that the inversion effect occurs for stimuli for which subjects have developed an expertise.     

Beyond U-Shaped Development in Infants' Processing of Faces: An Information-Processing Account

The development of the "inversion" effect in face processing was examined in infants 3 to 6 months of age by testing their integration of the internal and external features of upright and inverted faces using a variation of the "switch" visual habituation paradigm. When combined with previous findings showing that 7-month-olds use integrative processing of an upright face, but featural processing of an inverted face (Cohen & Cashon, 2001a), the present findings suggest that from 3 to 7 months, infants' ability to integrate facial features follows an N-shaped developmental pattern for upright faces and an inverted U-shaped pattern for inverted faces. We discuss these results in terms of a set of domain-general information-processing principles.     

Privileged detection of conspecifics: Evidence from inversion effects during continuous flash suppression

The rapid visual detection of other people in our environment is an important first step in social cognition. Here we provide evidence for selective sensitivity of the human visual system to upright depictions of conspecifics. In a series of seven experiments, we assessed the impact of stimulus inversion on the detection of person silhouettes, headless bodies, faces and other objects from a wide range of animate and inanimate control categories. We used continuous flash suppression (CFS), a variant of binocular rivalry, to render stimuli invisible at the beginning of each trial and measured the time upright and inverted stimuli needed to overcome such interocular suppression. Inversion strongly interfered with access to awareness for human faces, headless human bodies, person silhouettes, and even highly variable body postures, while suppression durations for control objects were not (inanimate objects) or only mildly (animal faces and bodies) affected by inversion. Furthermore, inversion effects were eliminated when the normal body configuration was distorted. The absence of strong inversion effects in a binocular control condition not involving interocular suppression suggests that non-conscious mechanisms mediated the effect of inversion on body and face detection during CFS. These results indicate that perceptual mechanisms that govern access to visual awareness are highly sensitive to the presence of conspecifics.     

The fidelity of visual memory for faces and non-face objects

The fidelity of visual working memory was assessed for faces and non-face objects. In two experiments, four levels of memory load (1, 2, 3, or 4 items) were combined with four perceptual distances between probe and study items, with maximum item confusability occurring for the minimum memory load. Under these conditions, recognition memory for multiple faces exceeded that of a single face. This result was primarily due to the higher false alarm rates for faces than non-face objects, even though the two classes of stimuli had been matched for perceptual discriminability. Control experiments revealed that this counterintuitive result emerged only for old–new recognition choices based on near-threshold image differences. For non-face objects, instead, recognition performance decreased with increasing memory load. It is speculated that the low memorial discriminability of the transient properties of a face may serve the purpose of enhancing recognition at the individual-exemplar level.