Abstract
Patients suffering from acquired prosopagnosia are unable to recognize familiar faces due to brain lesions in face-sensitive occipitotemporal regions. This neurological impairment is paired with suboptimal diagnostic information use during identity and facial expression recognition (FER). PS is a well-studied single case of AP with bilateral occipitotemporal lesions anatomically sparing the brain areas that are critical for FER: the amygdala, the insula, and the posterior superior temporal sulcus. PS shows impaired performance and reduced use of the eyes during static facial identification (e.g., Caldara et al., 2005) and FER (Fiset et al., 2017). In contrast, strikingly, she shows performance and representations within the normal range for the decoding of dynamic FER (Richoz et al., 2015). Nevertheless, PS’s visual sampling strategies during the decoding of the richer and more ecologically valid dynamic facial expressions of emotion (FEE) are still unknown. To this aim, we recorded the eye movements of PS and age-matched (AM) healthy controls while they performed a categorization task of the six static and dynamic basic FEE. All the observers showed an advantage for dynamic over static FER. iMap4 data-driven eye movement analyses (Lao et al., 2017) revealed that the fixation patterns underlying the recognition of static and dynamic expressions differed for both PS and AM controls. PS showed atypical fixation patterns compared to each AM control, with fewer fixations towards the eye region and prominent fixations over the mouth. Interestingly, despite this marked mouth-based bias, PS’s behavioral performance was within the normal range for all expressions in both conditions. Our data show that PS’s preferential mouth fixations enhance discrimination of all facial expression signals, regardless of the diagnostic value of this face region. PS developed an effective “suboptimal” strategy to accurately decode FEE, indicating that eye movement strategies are not strong predictors of FER performance in prosopagnosia.