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Flashed Face Distortion Effect: Grotesque Faces from Relative Spaces



We describe a novel face distortion effect resulting from the fast-paced presentation of eye-aligned faces. When cycling through the faces on a computer screen, each face seems to become a caricature of itself and some faces appear highly deformed, even grotesque. The degree of distortion is greatest for faces that deviate from the others in the set on a particular dimension (eg if a person has a large forehead, it looks particularly large). This new method of image presentation, based on alignment and speed, could provide a useful tool for investigating contrastive distortion effects and face adaptation.
We discovered an interesting face distortion effect while preparing a set of face images
for an identification experiment. We obtained a set of faces from a Slovakian data-
base (SmartNet IBC, no date) and eye-aligned them using PsychoMorph (Tiddeman
et al 2001). To check the consistency of the eye alignment, we started skimming through
the images on the computer at a fast pace. After a while, we made a few remarks to one
another about the `aesthetically challenged' faces in the set. They began to appear highly
deformed and grotesque. But after inspecting the especially ugly faces individually, each
of them appeared normal or even attractive.
It seemed that, after continuously flipping through the eye-aligned faces at a steady
rate, each one began to appear as a caricature of itself. If a person had a large jaw,
it looked particularly large, almost ogre-like. If a person had a slender nose, then it
looked remarkably thin. Many of the distortions, however, were quite difficult to artic-
ulate. If we stopped the sequence and returned to these particular faces, however, they
quickly returned to normal. We entertained the idea that Slavic faces were inherently
bizarre, but we replicated the effect with faces from several other databases.
We standardised the presentation rate and found that roughly 4 ^ 5 faces per second
appear highly distorted, even monstrous. The degree of distortion is greatest for faces
that deviate from the others in the set on a particular dimension. If one face has an
especially large or pronounced forehead compared to the others in the set, for example,
then it appears particularly bulbous.
Relative encoding seems to drive the effect. That is, forcing the observer to encode
each face in light of the others. By eye-aligning the faces, it becomes much easier to
compare their shape and the relative location of their features, so the differences between
them become more evident. The fast, steady presentation rate may also encourage this
relative encoding. If the faces are not eye-aligned or if they are presented too slowly or
quickly, then the effect lessens. Or, if we insert a brief gap in the sequence, the effect
almost completely disappears (see Movie 2).
This effect is most certainly related to work on adaptation, and the `face distortion
after effect' specifically (Webster and MacLin 1999). In the basic paradigm, participants
study a single artificially distorted face for a few seconds to several minutes followed
Flashed face distortion effect: Grotesque faces
from relative spaces
Perception, 2011, volume 40, pages 628 ^ 63 0
Jason M Tangen, Sean C Murphy, Matthew B Thompson
School of Psychology, University of Queensland, St Lucia, QLD 4072, Australia;
Received 24 March 2011, in revised form 26 May 2011; published online 6 July 2011
Abstract. We describe a novel face distortion effect resulting from the fast-paced presentation of
eye-aligned faces. When cycling through the faces on a computer screen, each face seems to become
a caricature of itself and some faces appear highly deformed, even grotesque. The degree of dis-
tortion is greatest for faces that deviate from the others in the set on a particular dimension (eg if a
person has a large forehead, it looks particularly large). This new method of image presentation,
based on alignment and speed, could provide a useful tool for investigating contrastive distortion
effects and face adaptation.
by an unaltered face that now appears distorted in the opposite direction to the adapting
face. Adaptation to a distorted face that is fat, happy, contracted, male, etc, causes
neutral faces to appear thin, sad, expanded, female, etc (see Hills et al 2010 for review).
Similar effects have been demonstrated for distortion effects of identity, ethnicity,
orientation, and attractiveness (Leopold et al 2001; Rhodes et al 2003, 2004; Webster
et al 2004).
There must, however, be some degree of homogeneity among the faces for the
outliers to stand out and for the effect to occur. The distortion effect, therefore, seems
to depend on the outlying dimensions among the images in the set, and these dimen-
sions do not seem to be limited to facial features or configurations. For example,
if a photograph is brightly lit compared to the others, then it appears overexposed.
Presumably, then, the effect relies on the same contrastive mechanism that gives rise
to shape-contrast effects. Suzuki and Cavanagh (1998), for example, demonstrated that
a briefly flashed line distorts a circle into an ellipse that appears elongated orthogo-
nally to the line orientation. Owing to the multidimensional nature of the faces in our
flashed face distortion effect, the resulting distortion is not on any single dimension,
but on every dimension along which the face images vary. In contrast, face distortion
after effects commonly result from prolonged exposure to one face with a single exagger-
ated dimension defined by the experimenter, such as the distance between the eyes.
The dimensions that can be caricatured in our effect, therefore, are not limited to those
that can be easily defined and modified by experimenters. For example, only Greeble
experts (Gauthier and Tarr 1997) could determine whether a Greeble's `belly horn' is
abnormally large or pointy (see Movie 3). Indeed, it becomes difficult to identify or label
the basis of the face distortions if the faces are rotated 1808(see Movie 4), much like the
Thatcher effect (Thompson 1980).
Traditionally, face adaptation effects have been interpreted within the framework
of Valentine's (1991) face-space model, in which faces are encoded by their positions in
a multidimensional space. A variety of similar metaphors have been used in conjunc-
tion with this model, such as a two-pool neural net and exemplar or prototype accounts
(Robbins et al 2007). While it is too early to know which model or theoretical framework
will be the most useful in defining this flashed face distortion effect, and predicting its
boundary conditions, face-space accounts or shape-contrast effects may serve as useful
starting points for investigating this interesting effect.
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ß 2 011 a Pion publication
630 J M Tangen, S C Murphy, M B Thompson
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ISSN 0301-006 6 (print) ISSN 1468-423 3 (electronic)
... One illusion that may be related to these effects is the flashed face distortion effect (Tangen, Murphy, & Thompson, 2011) : When eye-aligned faces are flashed continuously in the peripheral visual field, the faces start to look like caricatures of themselves, whereby different features of the face appear subjectively to be highly exaggerated and even grotesque. This phenomenologically vivid illusion may be related to the detection bias effects mentioned above because detection requires recognizing a stimulus as being different from the background or a norm. ...
... One critical feature of the flashed face distortion effect (Tangen et al., 2011) is that the illusion occurs only after a few repetitive flashes of different faces in the same locations in the periphery. Here we tested if this kind of temporal overloading would lead to color patches being perceived as more deviant from the norm or background, too (i.e., whether they would look more vividly colorful compared to a standard of the same saturation at a central location, which would not be preceded by flashes of similar color patch stimuli). ...
... Inspired by the dramatic and vivid nature of the flashed face distortion effect (Tangen et al. 2011) , here we attempted to test whether a similar illusion can be created with simple color stimuli. We reasoned that there may be a common general mechanism for the two cases: under some degree of processing overload induced by repetitive flashes of stimuli, peripheral perception may start to be biased towards seeing things as more deviant from the background or norm. ...
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A long-standing puzzle in perception concerns the subjective impression of vivid color experience in the periphery. While peripheral color processing is not entirely insensitive, the subjective vividness seems unsupported by the relative paucity of representation in the periphery. Inspired by the flashed face distortion effect, in which peripheral faces are perceived as somewhat exaggerated or distorted when they are preceded by flashes of other faces in the same location, we attempted to create an equivalent illusion in the domain of color. The hypothesis is that under temporal overload, patches of colorful dots may be perceived as more exaggerated in terms of saturation. We confirmed this hypothesis with the observation of a significant effect of modest magnitude, which was replicated in a second experiment. These results suggest that subjective inflation of perceived color saturation does occur in the periphery, when the perceptual system is sufficiently occupied temporally and spatially. We discuss the relationship between the observed effects with previous findings of liberal detection biases in the unattended periphery.
... As the faces are presented sequentially, they appear increasingly distorted and deformed. The effect was first observed accidently by Tangen, Murphy, and Thompson (2011), while scrolling through a set of eye-aligned Slovakian face images for an unrelated study (original stimulus available at Upon further investigation, they noted that the effect was increased when the faces were viewed eccentrically and greatest in faces for which the dimensions of one or more of the facial features deviated significantly from the others in the set (e.g., if one face has a particularly large forehead, it appeared even larger and bulbous in shape). ...
... Upon further investigation, they noted that the effect was increased when the faces were viewed eccentrically and greatest in faces for which the dimensions of one or more of the facial features deviated significantly from the others in the set (e.g., if one face has a particularly large forehead, it appeared even larger and bulbous in shape). The effect was also reduced by rotating the faces by 180 (Tangen et al., 2011). Further investigation by Utz and Carbon (2015) showed that the effect decreases significantly if the faces used are from different ethnic origins or species. ...
... The mechanism by which the FFDE arises remains unclear. Tangen et al. (2011) hypothesized that the FFDE is related to the face distortion aftereffect (FDAE), a phenomenon first discussed by Webster and MacLin (1999). The FDAE occurs when individuals are exposed to a distorted face image for an extended period of time. ...
The flashed face distortion effect is a phenomenon whereby images of faces, presented at 4–5 Hz in the visual periphery, appear distorted. It has been hypothesized that the effect is driven by cortical, rather than retinal, components. Here, we investigated the role of peripheral viewing on the effect. Normally sighted participants viewed the stimulus peripherally, centrally, and centrally with a blurring lens (to match visual acuity in the peripheral location). Participants rated the level of distortion using a Visual Analogue Scale. Although optical defocus did have a significant effect on distortion ratings, peripheral viewing had a much greater effect, despite matched visual acuity. We suggest three potential mechanisms for this finding: increased positional uncertainty in the periphery, reduced deployment of attention to the visual periphery, or the visual crowding effect.
... Relatedly, the temporal dynamics and time course of the Merry-or-Worry perception would also be interesting to explore. Illusory distortions of facial configuration leading to grotesque perceptual effects occur only with fast pace of alternating stimuli presentation (Tangen et al., 2011). This suggests that interpretation switch in the perception of our stimulus ought to be also fast. ...
... Neither should prosopometamorphopsia be confused with face adaptation (i.e., the finding that faces can be perceived slightly differently due to prior exposure to other faces; Webster & MacLeod, 2011). Finally, it should be distinguished from the flashed face distortion effect (also known as multiple-faces configuration), an experimentally induced illusion that involves a marked distortion of facial features when normal faces are presented in rapid succession to the peripheral visual field (Simas, Rocha, Sedycias, do Amaral, & de Menezes, 2008;Tangen, Murphy, & Tompson, 2011). Of note, patients with Alice in Wonderland syndrome may sometimes experience several types of metamorphopsia simultaneously but facial distortions only count as prosopometamorphopsia when non-facial distortions are of a different nature, such as plagiopsia (seeing things as being slanted), macrsomatognosia (experiencing one's own body as larger) or time distortions. ...
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Prosopometamorphopsia is an extremely rare disorder of visual perception characterised by facial distortions. We here review 81 cases (eight new ones and 73 cases published over the past century) to shed light on the perception of face gestalts. Our analysis indicates that the brain systems underlying the perception of face gestalts have genuine network properties, in the sense that they are widely disseminated and built such that spatially normal perception of faces can be maintained even when large parts of the network are compromised. We found that bilateral facial distortions were primarily associated with right-sided and bilateral occipital lesions, and unilateral facial distortions with lesions ipsilateral to the distorted hemifield or to the splenium of the corpus callosum. We also found tentative evidence for the involvement of the left frontal regions in the fusing of vertical hemi-images of faces, and of right parietal regions in the fusing of horizontal hemi-images. Evidence supporting the remarkable adaptability of the network comes from the relatively high recovery rates that we found, from the ipsilateral hemifield predominance of hemi-prosopometamorphopsia, and from a phenomenon called cerebral asthenopia (heightened visual fatigability) which points to the dynamic nature of compensatory mechanisms maintaining normal face perception, even in chronic cases of prosopometamorphopsia. Finally, our analysis suggests that specialised networks for the representation of face gestalts in familiar-versus-unfamiliar faces and for own-versus-other face may be present, although this is in need of further study.
... Due to this reduced sensitivity, they will underestimate the degree of changes. Interestingly, van Lier and Koning (2014) further revealed an overestimation of the real morphing range when they had to fixate on a stationary fixation dot-they assumed that this overestimation happened as a result of a figural face aftereffect (Carbon & Ditye, 2011, 2012Tangen et al., 2011;Webster & MacLin, 1999): through prolonged stationary fixation (between the eyes), differences in faces are perceived larger than they actually are. ...
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van Lier and Koning introduced the more-or-less morphing face illusion: The detection of changes in a constantly morphing face-sequence is strongly suppressed by fast eye saccades triggered by a moving fixation dot. Modulators of this intriguing effect were investigated with systematically varied facial stimuli (e.g., human faces from varying morphological groups, emotional states) and fixation location. Results replicated the overall pattern of moving fixations substantially reducing the sensitivity to detect transitions. Importantly, a deviation from real to perceived changes could only be detected when faces were altered in a way not happening in real world—by changing identity. When emotional states of faces were changed, people were capable of perceiving these changes: A situation very similar to everyday life where we might quickly inspect a face by executing fast eye saccades but where we are still aware of transient changes of the emotional state of the very same person.
... Similarly, many visual aftereffects increase in magnitude with eccentricity. These include tilt aftereffects (Harris & Calvert, 1985;Muir & Over, 1970), motion aftereffects (Castet, Keeble, & Verstraten, 2002;Wright, 1986), shape aftereffects (Gheorghiu, Kingdom, Bell, & Gurnsey, 2011;Suzuki & Cavanagh, 1998), and face aftereffects (Tangen, Murphy, & Thompson, 2011;Webster, Kaping, Mizokami, & Duhamel, 2004). Although the scaling of cortical magnification might explain the larger tilt aftereffect found in the periphery (Harris & Calvert, 1985), it cannot account for the eccentricitydependent increase in the shape aftereffect, and Gheorghiu et al. (2011) suggested that the differences might instead reflect greater adaptation gain (i.e., larger post-adaptation sensitivity suppression) or an eccentricity-dependent decrease in the stimulus-selectivity of the adapted mechanisms. ...
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Adaptation aftereffects are generally stronger for peripheral than for foveal viewing. We examined whether there are also differences in the dynamics of visual adaptation in central and peripheral vision. We tracked the time course of contrast adaptation to binocularly presented Gabor patterns in both the central visual field (within 5°) and in the periphery (beyond 10° eccentricity) using a yes/no detection task to monitor contrast thresholds. Consistent with previous studies, sensitivity losses were stronger in the periphery than in the center when adapting to equivalent high contrast (90% contrast) patterns. The time course of the threshold changes was fitted with separate exponential functions to estimate the time constants during the adapt and post-adapt phases. When adapting to equivalent high contrast, adaptation effects built up and decayed more slowly in the periphery compared with central adaptation. Surprisingly, the aftereffect in the periphery did not decay completely to the baseline within the monitored post-adapt period (400 s), and instead asymptoted to a higher level than for central adaptation. Even when contrast was reduced to one-third (30% contrast) of the central contrast, peripheral adaptation remained stronger and decayed more slowly. This slower dynamic was also confirmed at suprathreshold test contrasts by tracking tilt-aftereffects with a 2AFC orientation discrimination task. Our results indicate that the dynamics of contrast adaptation differ between central and peripheral vision, with the periphery adapting not only more strongly but also more slowly, and provide another example of potential qualitative processing differences between central and peripheral vision.
... The "Flashed Face Distortion Effect" (or FFDE) refers to a striking visual illusion in which faces presented sequentially in peripheral vision begin to look increasingly grotesque after just a few faces have been presented 1 . Most observers report large shape distortions, such that faces appear to have strange proportions, as well as distortions of color appearance that lead to faces that look too red, purple, or green. ...
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When normal faces are rapidly presented in the visual periphery, they are perceived as grotesque and distorted. This phenomenon, “The flashed-face distortion effect” (FFDE) is a powerful illusion that may reveal important properties of how faces are coded in peripheral vision. Despite the strength of the illusion (and its popularity), there has been almost no follow-up work to examine what governs the strength of the illusion or to develop a clear account of its phenomenology. Presently, our goal was to address this by manipulating aspects of facial appearance and spatial/temporal properties of the flashed-face stimulus to determine what factors modulate the illusion’s strength. In three experiments, we investigated the extent to which local contrast (operationalized by the presence or absence of makeup), image eccentricity, image size, face inversion, and presentation rate of images within the sequence each contributed to the strength of the FFDE. We found that some of these factors (eccentricity and presentation rate) mattered a great deal, while others (makeup, face inversion and image size) made little contribution to the strength of the FFDE. We discuss the implications of these results for a mechanistic account of the FFDE, and suggest several avenues for future research based on this compelling visual illusion.
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Prolonged exposure to a sensory stimulus induces perceptual adaptation aftereffects. Traditionally, aftereffects are known to change the appearance of stimulus features, like contrast, color, or shape. However, shifts in the spatial position of objects have also been observed to follow adaptation. Here, I demonstrate that visual adaptation produced by different adapter stimuli generates a bi-directional spatial repulsion. Observers had to judge the distance between a probe dot pair presented in the adapted region and compare them to a reference dot pair presented in a region not affected by adaptation. If the probe dot pair was present inside the adapted area, observers underestimated the distance. If, however, the dot pair straddled the adapted area, the distance was perceived as larger with a stronger distance expansion than compression. Bi-directional spatial repulsion was found with a similar magnitude for size and density adapters. Localization estimates with mouse pointing revealed that adaptation also affected absolute position judgments. Bi-directional spatial repulsion is most likely produced by the lines of adapter stimuli since single bars used as adapters were sufficient to induce spatial repulsion. Spatial repulsion was stronger for stimuli presented in the periphery. This finding explains why distance expansion is stronger than distance compression.
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The question of what peripheral vision is good for, especially in pattern recognition, is one of the most important and controversial issues in cognitive science. In a series of experiments, we provide substantial evidence that observers' behavioral performance in the periphery is consistently superior to central vision for topological change detection, while nontopological change detection deteriorates with increasing eccentricity. These experiments generalize the topological account of object perception in the periphery to different kinds of topological changes (i.e., including introduction, disappearance, and change in number of holes) in comparison with a broad spectrum of geometric properties (e.g., luminance, similarity, spatial frequency, perimeter, and shape of the contour). Moreover, when the stimuli were scaled according to cortical magnification factor and the task difficulty was well controlled by adjusting luminance of the background, the advantage of topological change detection in the periphery remained. The observed advantage of topological change detection in the periphery supports the view that the topological definition of objects provides a coherent account for object perception in peripheral vision, allowing pattern recognition with limited acuity.
Significant surround modulation was reported in the cortical areas corresponding to the periphery of the visual field, whereas no clear surround modulation was reported in the center. To understand the neural bases underlying the differences of the functions between the cortical areas corresponding to the center and periphery of the visual field, responses of the cells in the cat early visual cortex with their receptive fields in the center and periphery of the visual field were recorded by using multichannel electrodes, and cross-correlations of the spikes in the responses to the full-field stimuli, and the center-surround stimuli, which contained a grating in a central patch and a surround grating, were analyzed. Percentages of the cell pairs showing significant cross-correlation were larger in the cortical areas corresponding to the periphery than the center. In the center of the visual field, the percentages of the cell pairs showing significant cross-correlation significantly decreased as the separation of the recording points increased, and the time lags of the peaks of the cross-correlogram distributed around zero. In the periphery of the visual field, the time lags of the peaks of the cross-correlogram distributed more widely and increased as the separation of the recording points increased. In the responses to the center-surround stimuli in the preferred orientation of each cell, percentages of the cell pairs showing significant cross-correlation were larger in the periphery than the center. These results suggest that more lateral interactions occur in the cortical areas corresponding to the periphery than the center of the visual field.
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A framework is outlined in which individual faces are assumed to be encoded as a point in a multidimensional space, defined by dimensions that serve to discriminate faces. It is proposed that such a framework can account for the effects of distinctiveness, inversion, and race on recognition of faces. Two specific models within this framework are identified: a norm-based coding model, in which faces are encoded as vectors from a population norm or prototype, and a purely exemplar-based model. Both models make similar predictions, albeit in different ways, concerning the interactions between the effects of distinctiveness, inversion and race. These predictions were supported in five experiments in which photographs of faces served as stimuli. The norm-based coding version and the exemplar-based version of the framework cannot be distinguished on the basis of the experiments reported, but it is argued that a multidimensional space provides a useful heuristic framework to investigate recognition of faces. Finally, the relationship between the specific models is considered and an implementation in terms of parallel distributed processing is briefly discussed.
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Sensitivity to configural changes in face processing has been cited as evidence for face-exclusive mechanisms. Alternatively, general mechanisms could be fine-tuned by experience with homogeneous stimuli. We tested sensitivity to configural transformations for novices and experts with nonface stimuli ("Greebles"). Parts of transformed Greebles were identified via forced-choice recognition. Regardless of expertise level, the recognition of parts in the Studied configuration was better than in isolation, suggesting an object advantage. For experts, recognizing Greeble parts in a Transformed configuration was slower than in the Studied configuration, but only at upright. Thus, expertise with visually similar objects, not faces per se, may produce configural sensitivity.
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When a suprathreshold visual stimulus is flashed for 60-300 ms and masked, though it is no longer visibly degraded, the perceived shape is vulnerable to distortion effects, especially when a 2nd shape is present. Specifically, when preceded by a flashed line, a briefly flashed circle appears to be an ellipse elongated perpendicular to the line. Given an appropriate stimulus onset asynchrony, this distortion is perceived when the 2 stimuli (approximately 4 degrees) are presented as far as 12 degrees apart but is not due to perception of apparent motion between the 2 stimuli. Additional pairs of shapes defined by taper and overall curvature also revealed similar nonlocal shape distortion effects. The test shapes always appeared to be more dissimilar to the priming shapes, a distortion termed a shape-contrast effect. Its properties are consistent with the response characteristics of the shape-tuned neurons in the inferotemporal cortex and may reveal the underlying dimensions of early shape encoding.
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We examined figural aftereffects in images of human faces, for which changes in configuration are highly discriminable. Observers either matched or rated faces before or after viewing distorted images of faces. Prior adaptation strongly biases face perception by causing the original face to appear distorted in a direction opposite to the adapting distortion. Aftereffects transferred across different faces and were similar for upright or inverted faces, but were weaker when the adapting and test faces had different orientations (e.g., adapt inverted and test upright). Thus the aftereffects depend on which images are distorted, and not simply on the type of distortion introduced. We further show that the aftereffects are asymmetric, for adapting to the original face has little effect on the perception of a distorted face. This asymmetry suggests that adaptation may play an important normalizing role in face perception. Our results suggest that in normal viewing, figural aftereffects may strongly influence form perception and could provide a novel method for probing properties of human face perception.
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We used high-level configural aftereffects induced by adaptation to realistic faces to investigate visual representations underlying complex pattern perception. We found that exposure to an individual face for a few seconds generated a significant and precise bias in the subsequent perception of face identity. In the context of a computationally derived 'face space,' adaptation specifically shifted perception along a trajectory passing through the adapting and average faces, selectively facilitating recognition of a test face lying on this trajectory and impairing recognition of other faces. The results suggest that the encoding of faces and other complex patterns draws upon contrastive neural mechanisms that reference the central tendency of the stimulus category.
Adults can be adapted to a particular facial distortion in which both eyes are shifted symmetrically (Robbins, R., McKone, E., & Edwards, M. (2007). Aftereffects for face attributes with different natural variability: Adapter position effects and neural models. Journal of Experimental Psychology: Human Perception and Performance, 33, 570–592), but they do not show as great adaptation to an asymmetrical eye distortion. We adapted children and adolescents to symmetrical and asymmetrical eye distortions and measured the aftereffects. Children (aged 6–12, mean age 9 years) showed larger aftereffects than adolescents (aged 13–18, mean age 15 years) and demonstrated aftereffects of a similar magnitude for both asymmetrical and symmetrical distortions. Adolescents only showed aftereffects for symmetrical distortions. We propose that children may have a more flexible face norm and neural responses that allow a broader range of adapted states compared to adolescents.
Average faces are attractive, but what is average depends on experience. We examined the effect of brief exposure to consistent facial distortions on what looks normal (average) and what looks attractive. Adaptation to a consistent distortion shifted what looked most normal, and what looked most attractive, toward that distortion. These normality and attractiveness aftereffects occurred when the adapting and test faces differed in orientation by 90 degrees (+45 degrees vs. -45 degrees ), suggesting adaptation of high-level neurons whose coding is not strictly retino- topic. Our results suggest that perceptual adaptation can rapidly recalibrate people's preferences to fit the faces they see. The results also suggest that average faces are attractive because of their central location in a distribution of faces (i.e., prototypicality), rather than because of any intrinsic appeal of particular physical characteristics. Recalibration of preferences may have important consequences, given the powerful effects of perceived attractiveness on person perception, mate choice, social interactions, and social outcomes for individuals.
Face perception is fundamentally important for judging the characteristics of individuals, such as identification of their gender, age, ethnicity or expression. We asked how the perception of these characteristics is influenced by the set of faces that observers are exposed to. Previous studies have shown that the appearance of a face can be biased strongly after viewing an altered image of the face, and have suggested that these after-effects reflect response changes in the neural mechanisms underlying object or face perception. Here we show that these adaptation effects are pronounced for natural variations in faces and for natural categorical judgements about faces. This suggests that adaptation may routinely influence face perception in normal viewing, and could have an important role in calibrating properties of face perception according to the subset of faces populating an individual's environment.
Humans have an impressive ability to discriminate between faces despite their similarity as visual patterns. This expertise relies on configural coding of spatial relations between face features and/or holistic coding of overall facial structure. These expert face-coding mechanisms appear to be engaged most effectively by upright faces, with inverted faces engaging primarily feature-coding mechanisms. We show that opposite figural aftereffects can be induced simultaneously for upright and inverted faces, demonstrating that distinct neural populations code upright and inverted faces. This result also suggests that expert (upright) face-coding mechanisms can be selectively adapted. These aftereffects occur for judgments of face normality and face gender and are robust to changes in face size, ruling out adaptation of low-level, retinotopically organized coding mechanisms. Our results suggest a resolution of a paradox in the face recognition literature. Neuroimaging studies have found surprisingly little orientation selectivity in the fusiform face area (FFA) despite evidence that this region plays a role in expert face coding and that expert face-coding mechanisms are selectively engaged by upright faces. Our results, demonstrating orientation-contingent adaptation of face-coding mechanisms, suggest that the FFA's apparent lack of orientation selectivity may be an artifact of averaging across distinct populations within the FFA that respond to upright and inverted faces.