Visual perception and visual mental imagery of emotional faces generate similar expression aftereffects

What is the relationship between visual perception and visual mental imagery of emotional faces? We investigated this question using a within-emotion perceptual adaptation paradigm in which adaptation to a strong version of an expression was paired with a test face displaying a weak version of the same emotion category. We predicted that within-emotion adaptation to perception and imagery of expressions would generate similar aftereffects, biasing perception of weak emotional test faces toward a more neutral value. Our findings confirmed this prediction. Adaptation to mental images yielded aftereffects that inhibited emotion recognition of test expressions, as participants were less accurate at recognising these stimuli compared to baseline. While the same inhibitory effect was observed when expressions were visually perceived, the size of the aftereffects was greater for perception than imagery. These findings suggest the existence of expression-selective neural mechanisms that subserve both visual perception and visual mental imagery of emotional faces.     

Categorical perception of emotional facial expressions in preschoolers

Adults perceive emotional facial expressions categorically. In this study, we explored categorical perception in 3.5-year-olds by creating a morphed continuum of emotional faces and tested preschoolers’ discrimination and identification of them. In the discrimination task, participants indicated whether two examples from the continuum “felt the same” or “felt different.” In the identification task, images were presented individually and participants were asked to label the emotion displayed on the face (e.g., “Does she look happy or sad?”). Results suggest that 3.5-year-olds have the same category boundary as adults. They were more likely to report that the image pairs felt “different” at the image pair that crossed the category boundary. These results suggest that 3.5-year-olds perceive happy and sad emotional facial expressions categorically as adults do. Categorizing emotional expressions is advantageous for children if it allows them to use social information faster and more efficiently.     

Categorical perception of familiar objects

We report three experiments where the categorical perception of familiar, three-dimensional objects was investigated. A continuum of shape change between 15 pairs of objects was created and the images along the continuum were used as stimuli. In Experiment 1 participants were first required to discriminate pairs of images of objects that lay along the shape continuum. Then participants were asked to classify each morph-image into one of two pre-specified classes. We found evidence for categorical perception in some but not all of our object pairs. In Experiment 2 we varied the viewpoint of the objects in the discrimination task and found that effects of categorical perception generalized across changes in view. In Experiment 3 similarity ratings for each object pair were collected. These similarity scores correlated with the degree of perceptual categorization found for the object pairs. Our findings suggest that some familiar objects are perceived categorically and that categorical perception is closely tied to inter-object perceptual similarity.     

Categorical perception: effects of the extent and rate of spectral change

ABSTRACT

Two experiments evaluated a potential explanation of categorical perception (CP) for place of articulation – namely, that listeners derive limited information from rapid spectral changes. Experiment 1 examined vowel context effects for /b/–/d/ continua that included consonant–vowel tokens with F2 onset frequencies that varied systematically from the F2 frequencies of their corresponding steady-states. Phoneme categorisation sharply shifted with F2 direction at locations along the continuum where discrimination performance peaked, indicating CP. Experiment 2 compared findings for a replicated condition against conditions with vowels reduced to match consonant duration or consonants extended to match vowels. CP was similarly obtained for replicated and vowel-reduced conditions. However, listeners frequently perceived diphthongs centrally on the consonant-extended continuum. Some listeners demonstrated CP, although aggregate performance appeared more continuous. These experiments indicate a model based upon the perceived direction of frequency transitions.     

Categorical perception of tactile distance

The tactile surface forms a continuous sheet covering the body. And yet, the perceived distance between two touches varies across stimulation sites. Perceived tactile distance is larger when stimuli cross over the wrist, compared to when both fall on either the hand or the forearm. This effect could reflect a categorical distortion of tactile space across body-part boundaries (in which stimuli crossing the wrist boundary are perceptually elongated) or may simply reflect a localised increased in acuity surrounding anatomical landmarks (in which stimuli near the wrist are perceptually elongated). We tested these two interpretations across two experiments, by comparing a well-documented bias to perceive mediolateral tactile distances across the forearm/hand as larger than proximodistal ones along the forearm/hand at three different sites (hand, wrist, and forearm). According to the ‘categorical’ interpretation, tactile distances should be elongated selectively in the proximodistal axis thus reducing the anisotropy. According to the ‘localised acuity’ interpretation, distances will be perceptually elongated in the vicinity of the wrist regardless of orientation, leading to increased overall size without affecting anisotropy. Consistent with the categorical account, we found a reduction in the magnitude of anisotropy at the wrist, with no evidence of a corresponding localised increase in precision. These findings demonstrate that we reference touch to a representation of the body that is categorically segmented into discrete parts, which consequently influences the perception of tactile distance.     

The nature of learned categorical perception effects: a psychophysical approach

Categorical perception is often cited as a striking example of cognitive influences on perception. However, some evidence suggests the term is a misnomer, with effects based on cognitive not perceptual processing. Here, using a psychophysical approach, we provide evidence consistent with a learned categorical perception effect that is dependent on analysis within the visual processing stream. An improvement in participants' discrimination between grating patterns that they had learned to place in different categories was 'tuned' around the orientation of the patterns experienced during category learning. Thus, here, categorical perception may result from attentionally modulated perceptual learning about diagnostic category features, based upon orientation-selective stages of analysis. This argues strongly that category learning can alter our perception of the world.     

Familiarity effects on categorization levels of faces and objects

It is well established that faces, in contrast to objects, are categorized as fast or faster at the individual level (e.g., Bill Clinton) than at the basic-level (e.g., human face). This subordinate-shift from basic-level categorization has been considered an outcome of visual expertise with processing faces. However, in the present study we found that, similar to familiar faces, categorization of individually-known familiar towers is also faster at the individual level than at the basic-level in naïve participants. In addition, category-verification of familiar stimuli, at basic and superordinate levels, was slower and less accurate compared to unfamiliar stimuli. Thus, the existence of detailed semantic information, regardless of expertise, can induce a shift in the default level of object categorization from basic to individual level. Moreover, the individually-specific knowledge is not only more easily-retrieved from memory but it might also interfere with accessing more general category information.     

Slower access to visual awareness but otherwise intact implicit perception of emotional faces in schizophrenia-spectrum disorders

Schizophrenia-spectrum disorders are characterized by deficits in social domains. Extant research has reported an impaired ability to perceive emotional faces in schizophrenia. Yet, it is unclear if these deficits occur already in the access to visual awareness. To investigate this question, 23 people with schizophrenia or schizoaffective disorder and 22 healthy controls performed a breaking continuous flash suppression task with fearful, happy, and neutral faces. Response times were analysed with generalized linear mixed models. People with schizophrenia-spectrum disorders were slower than controls in detecting faces, but did not show emotion-specific impairments. Moreover, happy faces were detected faster than neutral and fearful faces, across all participants. Although caution is needed when interpreting the main effect of group, our findings may suggest an elevated threshold for visual awareness in schizophrenia-spectrum disorders, but an intact implicit emotion perception. Our study provides a new insight into the mechanisms underlying emotion perception in schizophrenia-spectrum disorders.     

Categorical perception of speech sounds in illiterate adults

Children affected by dyslexia exhibit a deficit in the categorical perception of speech sounds, characterized by both poorer discrimination of between-category differences and by better discrimination of within-category differences, compared to normal readers. These categorical perception anomalies might be at the origin of dyslexia, by hampering the set up of grapheme-phoneme correspondences, but they might also be the consequence of poor reading skills, as literacy probably contributes to stabilizing phonological categories. The aim of the present study was to investigate this issue by comparing categorical perception performances of illiterate and literate people. Identification and discrimination responses were collected for a /ba-da/ synthetic place-of-articulation continuum and between-group differences in both categorical perception and in the precision of the categorical boundary were examined. The results showed that illiterate vs. literate people did not differ in categorical perception, thereby suggesting that the categorical perception anomalies displayed by dyslexics are indeed a cause rather than a consequence of their reading problems. However, illiterate people displayed a less precise categorical boundary and a stronger lexical bias, both also associated with dyslexia, which might, therefore, be a specific consequence of written language deprivation or impairment.     

Categorical perception of colour in the left and right visual field is verbally mediated: evidence from Korean

In this study we demonstrate that Korean (but not English) speakers show Categorical perception (CP) on a visual search task for a boundary between two Korean colour categories that is not marked in English. These effects were observed regardless of whether target items were presented to the left or right visual field. Because this boundary is unique to Korean, these results are not consistent with a suggestion made by Drivonikou [Drivonikou, G. V., Kay, P., Regier, T., Ivry, R. B., Gilbert, A. L., Franklin, A. et al. (2007) Further evidence that Whorfian effects are stronger in the right visual field than in the left. Proceedings of the National Academy of Sciences 104, 1097-1102] that CP effects in the left visual field provide evidence for the existence of a set of universal colour categories. Dividing Korean participants into fast and slow responders demonstrated that fast responders show CP only in the right visual field while slow responders show CP in both visual fields. We argue that this finding is consistent with the view that CP in both visual fields is verbally mediated by the left hemisphere language system.     

Categorical perception of morphed objects using a free-naming experiment

Morphed figures entail a dominant and nondominant interpretation. Testing perception of morphed objects using forced-choice methods demonstrates that morphed figures are perceived as their dominant interpretation (“categorical perception”, or CP). Using a more natural free-naming response could reveal whether CP is an effect independent of method. In Experiment 1, therefore, series of morphed figures were tested for CP using free naming. Half of the morph series were identified as CP patterns. In Experiment 2, we used forced choice to investigate CP, resulting in an increase of number of CP series compared to free naming. The overlap between CP series of Experiments 1 and 2 was small, however. Experiment 3 revealed that higher perceptual similarity between the extremes of the series was strongly related to CP for the free-naming method, in contrast to the forced-choice method. We conclude that the observation of CP depends on the intactness of the intrinsic object structure caused by the morphing procedure.     

Adaptation and the perception of facial age

We examined how the perceived age of adult faces is affected by adaptation to younger or older adult faces. Observers viewed images of a synthetic male face simulating ageing over a modelled range from 15 to 65 years. Age was varied by changing shape cues or textural cues. Age level was varied in a staircase to find the observer's subjective category boundary between “old” and “young”. These boundaries were strongly biased by adaptation to the young or old face, with significant aftereffects induced by either shape or textural cues. A further experiment demonstrated comparable aftereffects for photorealistic images of average older or younger adult faces, and found that aftereffects showed some selectivity for a change in gender but also strongly transferred across gender. This transfer shows that adaptation can adjust to the attribute of age somewhat independently of other facial attributes. These findings suggest that perceived age, like many other natural facial dimensions, is highly susceptible to adaptation, and that this adaptation can be carried by both the structural and textural changes that normally accompany facial ageing.     

Electrophysiological markers of categorical perception of color in 7-month old infants

The origin of color categories has been debated by psychologists, linguists and cognitive scientists for many decades. Here, we present the first electrophysiological evidence for categorical responding to color before color terms are acquired. Event-related potentials were recorded on a visual oddball task in 7-month old infants. Infants were shown frequent presentations of one color (standard) interspersed with infrequent presentations of a color that was either from the same category (within-category deviant) or from a different category (between-category deviant) to the standard. Differences in the event-related potentials elicited by the stimuli were found that were related to the categorical relationship of the standard and the deviant stimuli. The data are discussed in relation to the processes that underlie categorical responding in infancy, as well as the debate about the origin of color categories in language and cognition.     

Allophonic mode of speech perception in dyslexia

Perceptual discrimination between speech sounds belonging to different phoneme categories is better than that between sounds falling within the same category. This property, known as "categorical perception," is weaker in children affected by dyslexia. Categorical perception develops from the predispositions of newborns for discriminating all potential phoneme categories in the world's languages. Predispositions that are not relevant for phoneme perception in the ambient language are usually deactivated during early childhood. However, the current study shows that dyslexic children maintain a higher sensitivity to phonemic distinctions irrelevant in their linguistic environment. This suggests that dyslexic children use an allophonic mode of speech perception that, although without straightforward consequences for oral communication, has obvious implications for the acquisition of alphabetic writing. Allophonic perception specifically affects the mapping between graphemes and phonemes, contrary to other manifestations of dyslexia, and may be a core deficit.     

Neurophysiological evidence for categorical perception of color

The aim of this investigation was to examine the time course and the relative contributions of perceptual and post-perceptual processes to categorical perception (CP) of color. A visual oddball task was used with standard and deviant stimuli from same (within-category) or different (between-category) categories, with chromatic separations for within- and between-category stimuli equated in Munsell Hue. CP was found on a behavioral version of the task, with faster RTs and greater accuracy for between- compared to within-category stimuli. On a neurophysiological version of the task, event-related potentials (ERPs) showed earlier latencies for P1 and N1 components at posterior locations to between- relative to within-category deviants, providing novel evidence for early perceptual processes on color CP. Enhanced P2 and P3 waves were also found for between- compared to within-category stimuli, indicating a role for later post-perceptual processes.     

Similar effects of visual perception and imagery on simple reaction time

A longstanding issue is whether perception and mental imagery share similar cognitive and neural mechanisms. To cast further light on this problem, we compared the effects of real and mentally generated visual stimuli on simple reaction time (RT). In five experiments, we tested the effects of difference in luminance, contrast, spatial frequency, motion, and orientation. With the intriguing exception of spatial frequency, in all other tasks perception and imagery showed qualitatively similar effects. An increase in luminance, contrast, and visual motion yielded a decrease in RT for both visually presented and imagined stimuli. In contrast, gratings of low spatial frequency were responded to more quickly than those of higher spatial frequency only for visually presented stimuli. Thus, the present study shows that basic dependent variables exert similar effects on visual RT either when retinally presented or when imagined. Of course, this evidence does not necessarily imply analogous mechanisms for perception and imagery, and a note of caution in such respect is suggested by the large difference in RT between the two operations. However, the present results undoubtedly provide support for some overlap between the structural representation of perception and imagery.     

It felt fluent but I did not like it: fluency effects in faces versus patterns

Whether you like a person or not is often appraised in a glance. However, under such short presentation durations stimuli are harder to perceive and, according to hedonic fluency theory-which holds that higher fluency is linked to higher liking-thus, are liked less. Given that liking considerably influences person perception, we tested how shorter and longer presentation durations affect liking for faces and compared this with abstract patterns. To capture facets of fluency of processing we assessed felt fluency, liking, and certainty ratings. Following predictions of fluency theory, longer presentation durations led to higher felt fluency, certainty, and positively affected liking judgments in the abstract patterns. In faces, felt fluency and certainty also increased with longer durations. However, with longer durations, faces were liked less, and liking was not related to felt fluency. In other words, in contrast to hedonic fluency theory, faces are more attractive when only seen for a short amount of time. Thus, fluency does not inevitably lead to more positive evaluations—it rather depends on the stimulus category. We discuss these findings in terms of the special status that faces have with regard to human perception and evaluation.     

Perceptual awareness and categorical representation of faces: evidence from masked priming

How internal categories influence how we perceive the world is a fundamental question in cognitive sciences. Yet, the relation between perceptual awareness and perceptual categorization has remained largely uncovered so far. Here, we addressed this question by focusing on face perception during subliminal and conscious perception. We used morphed continua between two face identities and we assessed, through a masked priming paradigm, the perceptual processing of these morphed faces under subliminal and supraliminal conditions. We found that priming from subliminal faces followed linearly the information present in the primes, while priming from visible faces revealed a non-linear profile, indicating a categorical processing of face identities. Our results thus point to a special relation between perceptual awareness and categorical processing of faces, and support the dissociation between two modes of information processing: a subliminal mode involving analog treatment of stimuli information, and a supraliminal mode relying on discrete representation.     

Ratings of emotion in laterally presented faces: sex and handedness effects

Sixteen right-handed participants (8 male and 8 female students) and 16 left-handed participants (8 male and 8 female students) were presented with cartoon faces expressing emotions ranging from extremely positive to extremely negative. A forced-choice paradigm was used in which the participants were asked to rate the faces as either positive or negative. Compared to men, women rated faces more positively, especially in response to right visual field presentations. Women rated neutral and mildly positive faces more positively in the right than in the left visual field, whereas men rated these faces consistently across visual fields. Handedness did not affect the ratings of emotion. The data suggest a positive emotional bias of the left hemisphere in women.