Processing deficits for familiar and novel faces in patients with left posterior fusiform lesions

Abstract

Pure alexia (PA) arises from damage to the left posterior fusiform gyrus (pFG) and the striking reading disorder that defines this condition has meant that such patients are often cited as evidence for the specialisation of this region to processing of written words. There is, however, an alternative view that suggests this region is devoted to processing of high acuity foveal input, which is particularly salient for complex visual stimuli like letter strings. Previous reports have highlighted disrupted processing of non-linguistic visual stimuli after damage to the left pFG, both for familiar and unfamiliar objects and also for novel faces. This study explored the nature of face processing deficits in patients with left pFG damage. Identification of famous faces was found to be compromised in both expressive and receptive tasks. Discrimination of novel faces was also impaired, particularly for those that varied in terms of second-order spacing information, and this deficit was most apparent for the patients with the more severe reading deficits. Interestingly, discrimination of faces that varied in terms of feature identity was considerably better in these patients and it was performance in this condition that was related to the size of the length effects shown in reading. This finding complements functional imaging studies showing left pFG activation for faces varying only in spacing and frontal activation for faces varying only on features. These results suggest that the sequential part-based processing strategy that promotes the length effect in the reading of these patients also allows them to discriminate between faces on the basis of feature identity, but processing of second-order configural information is most compromised due to their left pFG lesion. This study supports a view in which the left pFG is specialised for processing of high acuity foveal visual information that supports processing of both words and faces.

Word and text processing in developmental prosopagnosia

“…One study of four patients found impaired same-different judgments about facial identity and slow but accurate matching of faces across viewpoint changes (Behrmann & Plaut, 2014). A second study of 19 patients found slow but accurate matching of famous names to faces and reduced efficiency in same/different judgments about the spatial configuration of facial features (Roberts et al, 2015). On the other hand, two studies have reported a dissociation between face and visual word processing in pure alexia.…”

“…This hypothesis has received some neuropsychological support from a survey of patients with unilateral posterior cerebral arterial infarcts (Gerlach, Marstrand, Starrfelt, & Gade, 2014) and two studies showing faceprocessing deficits in alexic subjects (Behrmann & Plaut, 2014;Roberts et al, 2015). Studies of visual word processing in acquired prosopagnosia have produced mixed results, however.…”

A vision of graded hemispheric specialization

“…One recent study that investigated in some detail the face‐perception skills of pure alexic individuals observed that the sequential part‐based processing strategy that gives rise to the length effect in the reading by these patients apparently allows them to discriminate between faces on the basis of feature identity. In these individuals, the processing of second‐order configural information is compromised due to their left posterior FG lesion, suggesting that the deficit in face perception that emerges after the lesion is a reflection of the damage to the LH part‐processing bias per se rather than being a direct parallel of prosopagnosia after an RH lesion …”

Triangulation of the neurocomputational architecture underpinning reading aloud

“…The visually based reading deficit sometimes termed "pure alexia" is associated with damage to the left ventral occipitotemporal cortex (14,15), an area that is ubiquitously activated for tasks involving orthographic processing (8,16). Critically, such patients also have visual deficits for nonorthographic stimuli such as checkerboards and faces (15,17,18), supporting the primary systems view that this brain region is a more general visual-processing area. In a similar vein, patients with phonological dyslexia have concomitant phonological deficits in tasks that do not involve written words (19)(20)(21).…”