What Do Eye Movements Tell Us About the Visual Perception of Individuals With Congenital Prosopagnosia?

Objective: The lack of inversion effect for face recognition in congenital prosopagnosia (CP) is consistent with the hypothesis of a failure in holistic processing. However, although CPs' abnormal gaze behavior for upright faces has already been demonstrated, neither their scanning strategy for inverted faces, nor the possibility that their abnormal gaze behavior with upright faces is because of reasons other than the holistic deficit have been investigated yet. Method: We recorded the eye movements of a congenital prosopagnosic and a control group during the encoding of unknown faces, objects, and flowers. Two types of stimuli (faces and objects) were presented upright and inverted. Results: CPs explored upright and inverted faces in the same way (i.e., similar number of fixations of the same duration and similarly distributed), whereas controls increased the number of fixations and their duration during the presentation of inverted faces. By contrast, the 2 groups showed a similar inversion effect during the encoding of objects. Finally, CPs showed anomalous exploration of within-class objects (i.e., flowers) and impairment in subordinate-level object discrimination. Conclusions: Our results demonstrate that: (a) CPs use the same part-based strategy in encoding both upright and inverted faces, suggesting a possible interpretation of the lack of inversion effect in this population; (b) CPs' lack of inversion effect is face-specific and does not affect objects; (c) however, CPs' deficit seems not to be limited to faces, and to extend to individual-item recognition within a class. General Scientific Summary This study suggests that people with a low performance in face recognition from birth (i.e., congenital prosopagnosics) have also some difficulties in recognizing stimuli with a high degree of similarity, such as objects belonging to the same class (e.g., gerberas), and that these difficulties are associated with a different pattern of visual exploration.