Papers by Philip Pell
Autism spectrum conditions (ASC) are associated with a number of atypicalities in face processing... more Autism spectrum conditions (ASC) are associated with a number of atypicalities in face processing, including difficulties in face memory. However, the neural mechanisms underlying this difficulty are unclear. In neurotypical individuals, repeated presentation of the same face is associated with a reduction in activity, known as repetition suppression (RS), in the fusiform face area (FFA). However, to date, no studies have investigated RS to faces in individuals with ASC, or the relationship between RS and face memory. Here, we measured RS to faces and geometric shapes in individuals with a clinical diagnosis of an ASC and in age and IQ matched controls. Relative to controls, the ASC group showed reduced RS to faces in bilateral FFA and reduced performance on a standardized test of face memory. By contrast, RS to shapes in object-selective regions and object memory did not differ between groups. Individual variation in face-memory performance was positively correlated with RS in regions of left parietal and prefrontal cortex. These findings suggest difficulties in face memory in ASC may be a consequence of differences in the way faces are stored and/or maintained across a network of regions involved in both visual perception and short-term/working memory.
Background: Autism Spectrum Conditions (ASC) are associated with a range of perceptual atypicalit... more Background: Autism Spectrum Conditions (ASC) are associated with a range of perceptual atypicalities, including abnormalities in gaze processing. Pellicano and Burr (Trends Cogn Sci 16(10):504-10, 2012) have argued that these atypicalities might be explained within a Bayesian framework, in which perception represents the combination of sensory information with prior knowledge. They propose that the Bayesian priors of individuals with ASC might be attenuated, such that their perception is less reliant on prior knowledge than neurotypical individuals. An important tenet of Bayesian decision theory is that increased uncertainty about incoming sensory information will lead to a greater influence of the prior on perception. Consistent with this, Mareschal et al. (Curr Biol 23(8):717-21, 2013) showed that when noise is added to the eyes of a face (increasing uncertainty about gaze direction), gaze is more likely to be perceived as direct. Methods: We adopted the same paradigm as Mareschal et al. to determine whether the influence of a prior on gaze perception is reduced in neurotypical participants with high numbers of autistic traits (experiment 1) and in individuals with a clinical diagnosis of ASC (experiment 2). Participants were presented with synthetic faces and asked to make a judgement about the relative gaze directions of the faces. Uncertainty about gaze direction was manipulated by adding noise to the eyes of a face. Results: Consistent with previous work, in both experiment 1 and experiment 2, participants showed a bias towards perceiving gaze as direct under conditions of uncertainty. However, there was no evidence that the magnitude of this bias was reduced either in the ASC group or in neurotypical controls with a high number of autistic traits.
The human ventral temporal cortex (VTC) plays a critical role in object recognition. Although it ... more The human ventral temporal cortex (VTC) plays a critical role in object recognition. Although it is well established that visual experience shapes VTC object representations, the impact of semantic and contextual learning is unclear. In this study, we tracked changes in representations of novel visual objects that emerged after learning meaningful information about each object. Over multiple training sessions, participants learned to associate semantic features (e.g., "made of wood," "floats") and spatial contextual associations (e.g., "found in gardens") with novel objects. fMRI was used to examine VTC activity for objects before and after learning. Multivariate pattern similarity analyses revealed that, after learning, VTC activity patterns carried information about the learned contextual associations of the objects, such that objects with contextual associations exhibited higher pattern similarity after learning. Furthermore, these learning-induced increases in pattern information about contextual associations were correlated with reductions in pattern information about the object's visual features. In a second experiment, we validated that these contextual effects translated to real-life objects. Our findings demonstrate that visual object representations in VTC are shaped by the knowledge we have about objects and show that object representations can flexibly adapt as a consequence of learning with the changes related to the specific kind of newly acquired information.
Social Neuroscience
An adaptation paradigm was used to investigate the influence of a previously experienced visual c... more An adaptation paradigm was used to investigate the influence of a previously experienced visual context on the interpretation of ambiguous emotional expressions. Affective classification of fear-neutral ambiguous expressions was performed following repeated exposure to either fearful or neutral faces. There was a shift in the behavioural classification of morphs towards ‘fear’ following adaptation to neutral compared to adaptation to fear with a non-significant trend towards the high anxiety group compared to the low being more influenced by the context. The event-related potential (ERP) data revealed a more pronounced late positive potential (LPP), beginning at ~400 ms post-stimulus onset, in the high but not the low anxiety group following adaptation to neutral compared to fear. In addition, as the size of the behavioural adaptation increased there was a linear increase in the magnitude of the late-LPP. However, context-sensitivity effects are not restricted to trait anxiety, with similar effects observed with state anxiety and depression. These data support the proposal that negative moods are associated with increased sensitivity to visual contextual influences from top-down elaborative modulations, as reflected in an enhanced late positive potential deflection.
Vision Research
Influential cognitive models of face perception posit that facial expression and identity are pro... more Influential cognitive models of face perception posit that facial expression and identity are processed by independent visual systems. Recent research indicates these systems interact and that representations of different expressions also interact. Here we used a visual adaptation paradigm to test whether the overlapping visual representations of anger and disgust expressions are modulated by identity. In Experiment 1, adaptation to a disgust face biased perception away from anger when the adaptation and target face were congruent in identity. When the adaptation and target face were incongruent in identity this effect was significantly smaller, also, the magnitude of identity-dependency was not affected by target expression. Experiment 2 demonstrated the same modulating effect of identity when stimulus-specific effects are controlled. These results indicate that the facial expression system consists of identity-independent and identity-dependent elements within a representational framework supporting overlapping expression representations.
Increasing evidence suggests that the visual representations of different emotional facial expres... more Increasing evidence suggests that the visual representations of different emotional facial expressions overlap. Here we used an adaptation paradigm to investigate overlap of anger, disgust and fear expressions. In Experiment 1, participants categorized faces morphed from neutral to anger or neutral to disgust after adaptation to expressions of anger, disgust, and fear. Adaptation to expressions of both anger and disgust was found to bias perception of anger expressions away from anger. For disgust expressions, adaptation to disgust biased perception away from disgust, whereas fear adaptation biased perception towards disgust. Adaptation to anger had no measurable effect. In Experiment 2, covering the mouth-region of the disgust adaptation face was found to severely diminish the effect of disgust adaptation on perception of anger targets whereas covering the nose- or eye-region had no effect. In Experiment 3, adaptation to anger had a substantial effect on perception of anger targets when the mouth-region of the anger face was covered; indicating that the results of Experiment 2 are not an artefact of the stimuli and procedures used. These results indicate that the visual representations of anger, disgust and fear expressions overlap to a considerable degree. Furthermore, the nature of this overlap appears related to the communicative functions of these expressions.
Conference Presentations by Philip Pell
In neuroimaging studies, repetitions of the same stimulus typically result in a reduction in neur... more In neuroimaging studies, repetitions of the same stimulus typically result in a reduction in neural activity, known as repetition suppression (RS). Repeated presentation of the same face is associated with RS in core regions of the face processing network, including the fusiform face area (FFA). At a behavioural level, repeated viewing of the same stimulus causes a change in perceptual sensitivity, known as a visual aftereffect. Evidence indicates that visual aftereffects for faces are attenuated in children and adolescents with autism spectrum conditions (ASC), leading to the proposal that atypical adaptive coding in face processing networks may underlie difficulties in face learning and memory found in ASC. However, whether individuals with ASC show reduced RS to faces remains to be addressed. Here, we used functional MRI to investigate RS to faces and non-faces (simple geometric shapes) in adults with a clinical diagnosis of ASC. We measured activity in face- and object-selective regions of occipitotemporal cortex while participants viewed blocks of images comprising repetitions of the same face/shape or images of different faces/shapes. Participants also completed standardized behavioural tests of face and car memory. Relative to age and IQ matched controls, individuals with ASC showed diminished RS to faces in right FFA. By contrast, RS to shapes in object-selective regions did not differ between groups. This finding could not be explained by differences in gaze fixations or face-selectivity in FFA. In addition, behavioural data revealed that individuals with ASC showed a significant impairment in face memory (compared to controls) but not car memory. These findings suggest reduced RS in FFA as a possible neural mechanism underlying attenuated facial aftereffects found in ASC, and suggest that differences in the adaptive properties of the face-processing network may underlie difficulties in face learning and memory associated with this condition. Meeting abstract presented at VSS 2015.
Autism Spectrum Conditions (ASC) are characterized by a range of perceptual atypicalities, includ... more Autism Spectrum Conditions (ASC) are characterized by a range of perceptual atypicalities, including abnormalities in gaze processing. Pellicano and Burr (2012) recently proposed that perceptual atypicalities might be a consequence of attenuated priors in ASC (i.e. reduced influence of prior knowledge on the perception of sensory information). Evidence from neurotypical populations indicates that under conditions of uncertainty (created by adding noise to the eyes of face stimuli), gaze is more likely to be perceived as direct (Mareschal et al., 2013), suggesting that humans have a prior expectation that other people's gaze is directed toward them. Here we adopted the same paradigm to address two questions: 1) Is the influence of priors on gaze perception reduced as a function of autistic traits within a neurotypical population (Experiment 1)? 2) Do individuals with diagnosis of ASC show evidence for reduced influence of gaze priors (Experiment 2)? Each experiment began with a staircase procedure designed to tailor the noise contrast required for each participant to perform a left/right gaze discrimination at 80% correct. Participants were then required to judge the relative gaze directions of two faces when noise was added to the eyes of one face only. In Experiment 1, participants showed a significant bias towards perceiving uncertain gaze as direct, however this bias was not related to increasing autistic traits. In Experiment 2, individuals with ASC showed a robust direct gaze prior comparable to that of IQ matched controls. Given that noise-thresholds did not differ across groups, this finding is unlikely to reflect a combination of attenuated priors and increased sensory noise in ASC. These results pose a challenge to the hypoprior Bayesian model of ASC and suggest that if ASC is characterized by atypicalities in the use of prior information this is not reflected in their performance on a gaze task
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Papers by Philip Pell
Conference Presentations by Philip Pell