Touching up on faces: A multisensory perspective on acquiring expertise with faces: [Gesichter neu erfassen: Eine multisensorische Perspektive auf die Erlangung von Expertise für Gesichter]

Faces are often considered to be different from other object categories both because of the sociobiological necessity for humans to differentiate members of their own group, and because of the differences in cognitive demands for face perception relative to general object recognition. A tremendous amount of research has shown that human observers are experts at visual face recognition due to specialized visual mechanisms for face processing that evolve with perceptual expertise. In this Ph.D. thesis, we introduce haptic face processing as a tool for studying the mechanisms underlying face processing expertise from new angles. In the first study, we tested face recognition within and across the haptic and visual modalities. We showed that both the haptic and visual systems have the capacity to process faces, and that face-relevant information can be shared across sensory modalities. Interestingly, we found this information transfer across modalities to be asymmetric and limited by haptic face processing. In the second study, we investigated whether and how the way in which haptic information is gathered affects the encoding, processing and storage of that information and consequently how it affects face recognition performance. This was achieved by using a gaze-restricted display to constrain the visual system to sequential, self-directed exploration, promoting serial encoding in vision in much the same way that the haptic system encodes objects. We found that face recognition was equally disrupted using gaze-restricted vision and haptics as compared to unrestricted vision with a clear switch from configural to featural processing. In the third study, we focused on the role of perceptual expertise on information processing of serially encoded faces using a gaze-restricted display, i.e. whether participants can learn to efficiently recognize faces that are serially encoded. We showed that practice with a previously novel way of perceiving faces, i.e. through serial encoding, can lead to some of the recognition effects typically associated with unrestricted visual face recognition, indicating that – at least for vision - serial encoding of information might allow for expert face processing. In the fourth study, we used a different approach to the question how perceptual expertise shapes efficient face processing strategies by studying haptic face recognition in the sighted, congenitally blind, and acquired blind. Our results demonstrated the crucial role of visual input for the development of efficient face processing capabilities inasmuch as a lack of relevant visual experience cannot be compensated for or improved by purely perceptual haptic expertise. Overall the thesis highlights how modality-specific differences in information acquisition affect processing strategies in high-level tasks, such as face recognition, and under which conditions those differences can be compensated for by perceptual expertise. Studying haptic face processing (and its contribution in a cross-modal context) is, therefore, a valuable new tool for studying face processing itself, the mental representation and the role of perceptual expertise, but also the differences and commonalities of information processing in the visual and haptic modalities