Alison Harris

The fusiform face area is selective for faces not animals

To test whether the human fusiform face area (FFA) responds not only to faces but to anything human or animate, we used fMRI to measure the response of the FFA to six new stimulus categories. The strongest responses were to stimuli containing faces: human faces (2.0% signal increase from fixation baseline) and human heads (1.7%), with weaker but still strong responses to whole humans (1.5%) and animal heads (1.3%). Responses to whole animals (1.0%) and human bodies without heads (1.0%) were significantly stronger than responses to inanimate objects (0.7%), but responses to animal bodies without heads (0.8%) were not. These results demonstrate that the FFA is selective for faces, not for animals.

Perception of face parts and face configurations: An fmri study

fMRI studies have reported three regions in human ventral visual cortex that respond selectively to faces: the occipital face area (OFA), the fusiform face area (FFA), and a face-selective region in the superior temporal sulcus (fSTS). Here, we asked whether these areas respond to two first-order aspects of the face argued to be important for face perception, face parts (eyes, nose, and mouth), and the T-shaped spatial configuration of these parts. Specifically, we measured the magnitude of response in these areas to stimuli that (i) either contained real face parts, or did not, and (ii) either had veridical face configurations, or did not. The OFA and the fSTS were sensitive only to the presence of real face parts, not to the correct configuration of those parts, whereas the FFA was sensitive to both face parts and face configuration. Further, only in the FFA was the response to configuration and part information correlated across voxels, suggesting that the FFA contains a unified representation that includes both kinds of information. In combination with prior results from fMRI, TMS, MEG, and patient studies, our data illuminate the functional division of labor in the OFA, FFA, and fSTS.

The representation of parts and wholes in face-selective cortex

Although face perception is often characterized as depending on holistic, rather than part-based, processing, there is behavioral evidence for independent representations of face parts. Recent work has linked face-selective regions defined with functional magnetic resonance imaging (fMRI) to holistic processing, but the response of these areas to face parts remains unclear. Here we examine part-based versus holistic processing in face-selective visual areas using face stimuli manipulated in binocular disparity to appear either behind or in front of a set of stripes [Nakayama, K., Shimojo, S., & Silverman, G. H. Stereoscopic depth: Its relation to image segmentation, grouping, and the recognition of occluded objects. Perception, 18, 5568, 1989]. While the first case will be filled in by the visual system and perceived holistically, we demonstrate behaviorally that the latter cannot be completed amodally, and thus is perceived as parts. Using these stimuli in fMRI, we found significant responses to both depth manipulations in inferior occipital gyrus and middle fusiform gyrus (MFG) face-selective regions, suggesting that neural populations in these areas encode both parts and wholes. In comparison, applying these depth manipulations to control stimuli (alphanumeric characters) elicited much smaller signal changes within face-selective regions, indicating that the part-based representation for faces is separate from that for objects. The combined adaptation data also showed an interaction of depth and familiarity within the right MFG, with greater adaptation in the back (holistic) condition relative to parts for familiar but not unfamiliar faces. Together, these data indicate that face-selective regions of occipito-temporal cortex engage in both part-based and holistic processing. The relative recruitment of such representations may be additionally influenced by external factors such as familiarity.

Neural Tuning for Face Wholes and Parts in Human Fusiform Gyrus Revealed by fMRI Adaptation

Although the right fusiform face area (FFA) is often linked to holistic processing, new data suggest this region also encodes part-based face representations. We examined this question by assessing the metric of neural similarity for faces using a continuous carryover functional MRI (fMRI) design. Using faces varying along dimensions of eye and mouth identity, we tested whether these axes are coded independently by separate part-tuned neural populations or conjointly by a single population of holistically tuned neurons. Consistent with prior results, we found a subadditive adaptation response in the right FFA, as predicted for holistic processing. However, when holistic processing was disrupted by misaligning the halves of the face, the right FFA continued to show significant adaptation, but in an additive pattern indicative of part-based neural tuning. Thus this region seems to contain neural populations capable of representing both individual parts and their integration into a face gestalt. A third experiment, which varied the asymmetry of changes in the eye and mouth identity dimensions, also showed part-based tuning from the right FFA. In contrast to the right FFA, the left FFA consistently showed a part-based pattern of neural tuning across all experiments. Together, these data support the existence of both part-based and holistic neural tuning within the right FFA, further suggesting that such tuning is surprisingly flexible and dynamic.

Dissociable Processing of Emotional and Neutral Body Movements Revealed by μ-Alpha and Beta Rhythms

Abstract Both when actions are executed and observed, electroencephalography (EEG) has shown reduced alpha-band (8–12 Hz) oscillations over sensorimotor cortex. This ‘μ-alpha’ suppression is thought to reflect mental simulation of action, which has been argued to support internal representation of others’ emotional states. Despite the proposed role of simulation in emotion perception, little is known about the effect of emotional content on μ-suppression. We recorded high-density EEG while participants viewed point-light displays of emotional vs neutral body movements in ‘coherent’ biologically plausible and ‘scrambled’ configurations. Although coherent relative to scrambled stimuli elicited μ-alpha suppression, the comparison of emotional and neutral movement, controlling for basic visual input, revealed suppression effects in both alpha and beta bands. Whereas alpha-band activity reflected reduced power for emotional stimuli in central and occipital sensors, beta power at frontocentral sites was driven by enhancement for neutral relative to emotional actions. A median-split by autism-spectrum quotient score revealed weaker μ-alpha suppression and beta enhancement in participants with autistic tendencies, suggesting that sensorimotor simulation may be differentially engaged depending on social capabilities. Consistent with theories of embodied emotion, these data support a link between simulation and social perception while more firmly connecting emotional processing to the activity of sensorimotor systems.

Embodied Valuation: Directional Action is Associated with Item Values

We have a lifetime of experience interacting with objects we value. Although many economic theories represent valuation as a purely cognitive process independent of the sensorimotor system, embodied cognitive theory suggests that our memories for items’ value should be linked to actions we use to obtain them. Here, we investigated whether the value of real items was associated with specific directional movements toward or away from the body. Participants priced a set of food items to determine their values; they then used directional actions to classify each item as high- or low-value. To determine if value is linked to specific action mappings, movements were referenced either with respect to the object (push toward high-value items; pull away from low-value items) or the self (pull high-value items toward self; push low-value items away). Participants who were assigned (Experiment 1) or chose (Experiment 2) to use an object-referenced action mapping were faster than those using a self-referenced mapping. A control experiment (Experiment 3) using left/right movements found no such difference when action mappings were not toward/away from the body. These results indicate that directional actions toward items are associated with the representation of their value, suggesting an embodied component to economic choice.

Loss Aversion Reflects Information Accumulation, Not Bias: A Drift-Diffusion Model Study

Defined as increased sensitivity to losses, loss aversion is often conceptualized as a cognitive bias. However, findings that loss aversion has an attentional or emotional regulation component suggest that it may instead reflect differences in information processing. To distinguish these alternatives, we applied the drift-diffusion model (DDM) to choice and response time (RT) data in a card gambling task with unknown risk distributions. Loss aversion was measured separately for each participant. Dividing the participants into terciles based on loss aversion estimates, we found that the most loss-averse group showed a significantly lower drift rate than the other two groups, indicating overall slower uptake of information. In contrast, neither the starting bias nor the threshold separation (barrier) varied by group, suggesting that decision thresholds are not affected by loss aversion. These results shed new light on the cognitive mechanisms underlying loss aversion, consistent with an account based on information accumulation.

Holistic Processing of Body Postures

Although research supports the idea that faces are processed holistically, less evidence exists for the holistic processing of bodies. The body has more degrees of freedom, making it a challenge to distinguish between holistic and configural processing via traditional tests of holistic processing (e.g., the composite effect). Here, we test for the holistic processing of body postures using a stereoscopic manipulation to create either the percept of a whole body occluded by a set of bars or segments of body floating in front of a background. Despite having identical low-level properties, only the first stimulus is perceived holistically due to filling-in via amodal completion. These stimuli were presented in a modified version of the whole-versus-part superiority paradigm (Tanaka & Farah, 1993) in which subjects were asked to identify body parts either in isolation or within the context of a body. In line with previous results for faces, our current data suggest that recognition performance was better for body parts in the whole-body condition, relative to isolated parts and for conditions where the body was perceived to be whole behind the bars. Additionally, it appears that the whole-part difference is greater for stereoscopic conditions where the body is perceived to be intact behind the bars rather than as floating body segments. These findings support the idea that bodies, like faces, can be processed in a holistic manner, laying the groundwork for further research using this paradigm. Meeting abstract presented at VSS 2015.

Dissociable temporal components of neural similarity in face perception: An ERP study

Psychological models suggest that perceptual similarity can be divided into geometric effects, such as metric distance in stimulus space, and non-geometric effects, such as stimulusspecific biases. We investigated the neural and temporal separability of these effects in a carry-over, event-related potential (ERP) study of facial similarity. By testing this dual effects model against a temporal framework of visual evoked components, we demonstrate that the behavioral distinction between geometric and non-geometric similarity effects is consistent with dissociable neural responses across the time course of face perception.