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Allison Yamanashi Leib, Amrita Puri, Shlomo Bentin, David Whitney, Lynn Robertson; Ensemble Encoding in Congenital Prosopagnosia. Journal of Vision 2011;11(11):575. doi: https://doi.org/10.1167/11.11.575.
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© ARVO (1962-2015); The Authors (2016-present)
Individuals with congenital/developmental prosopagnosia have difficulty recognizing faces. They also have been reported to have difficulty with more global processing of other types of complex stimuli. Here, we tested for both of these effects using a single common stimulus display, so that the two deficits could be directly compared in the same experiment. We presented groups of faces, because typical observers precisely perceive the mean of the ensemble expression or identity in such groups. We created an identity stimulus set, or “wheel”, by morphing incrementally between three distinct identities from the Ekman face gallery. Additionally, using only one identity from the gallery, we created an emotion stimulus wheel by morphing between the happy, angry, and sad versions of that face. During the experiment, congenital prosopagnosics and matched controls viewed sets of 18 faces varying in either identity or emotion (in separate blocks), and were asked to estimate the average identity or emotion of each set. Participants responded by choosing the identity or emotion from the stimulus wheel that corresponded to their perception of the average. Importantly, the face sets were presented in both upright and inverted viewing orientations (in separate blocks). For upright face sets, prosopagnosics were impaired in their ability to estimate the average for both the emotion and identity tasks. In contrast, prosopagnosics performed equivalently or better than controls in the inverted conditions in both tasks. These findings suggest that prosopagnosics are capable of extracting ensemble information about low-level features in faces, but are impaired at high-level (upright face specific) ensemble perception.
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