Acquired prosopagnosia without word recognition deficits

Abstract

It has long been suggested that face recognition relies on specialized mechanisms that are not involved in visual recognition of other object categories, including those that require expert, fine-grained discrimination at the exemplar level such as written words. But according to the recently proposed many-to-many theory of object recognition (MTMT), visual recognition of faces and words are carried out by common mechanisms [Behrmann, M., & Plaut, D. C. ( 2013 ). Distributed circuits, not circumscribed centers, mediate visual recognition. Trends in Cognitive Sciences, 17, 210-219]. MTMT acknowledges that face and word recognition are lateralized, but posits that the mechanisms that predominantly carry out face recognition still contribute to word recognition and vice versa. MTMT makes a key prediction, namely that acquired prosopagnosics should exhibit some measure of word recognition deficits. We tested this prediction by assessing written word recognition in five acquired prosopagnosic patients. Four patients had lesions limited to the right hemisphere while one had bilateral lesions with more pronounced lesions in the right hemisphere. The patients completed a total of seven word recognition tasks: two lexical decision tasks and five reading aloud tasks totalling more than 1200 trials. The performances of the four older patients (3 female, age range 50-64 years) were compared to those of 12 older controls (8 female, age range 56-66 years), while the performances of the younger prosopagnosic (male, 31 years) were compared to those of 14 younger controls (9 female, age range 20-33 years). We analysed all results at the single-patient level using Crawford's t-test. Across seven tasks, four prosopagnosics performed as quickly and accurately as controls. Our results demonstrate that acquired prosopagnosia can exist without word recognition deficits. These findings are inconsistent with a key prediction of MTMT. They instead support the hypothesis that face recognition is carried out by specialized mechanisms that do not contribute to recognition of written words.

Word and text processing in developmental prosopagnosia

“…Three reports on acquired prosopagnosia have examined the word-length effect. One found elevated word-length effects in three subjects (Behrmann & Plaut, 2014), but as others have pointed out (Hills et al, 2015;Susilo et al, 2015), interpreting these data is complicated by the fact that the subjects have been described elsewhere as having an integrative agnosia (Behrmann & Kimchi, 2003). On the other hand, two studies have demonstrated a dissociation between visual word and face processing in acquired prosopagnosia.…”

“…Hence one must be cautious about the implications of normal reading in developmental prosopagnosia for the many-to-many hypothesis until more is known about which components of the face-processing network are dysfunctional in this disorder. In this regard, evidence of normal visual word processing in subjects with acquired prosopagnosia from unilateral right fusiform lesions (Hills et al, 2015;Susilo et al, 2015) is a more significant challenge to the many-to-many hypothesis.…”

“…While elevated word-length effects were demonstrated in four subjects with prosopagnosia after bilateral lesions, five subjects with prosopagnosia after right anterior temporal or right fusiform lesions showed no evidence of reading impairment (Hills et al, 2015). Similarly, word-length effects in lexical decision and reading aloud tasks were evaluated in five subjects with acquired prosopagnosia, four with unilateral lesions and two with fusiform lesions: Only one subject had consistent problems (Susilo et al, 2015).…”

“…However, a second report on 11 subjects found elevated word-length effects only in those subjects with bilateral lesions (Hills, Pancaroglu, Duchaine, & Barton, 2015). A third study found an elevated wordlength effect and other signs of impaired reading in only one of five subjects with acquired prosopagnosia (Susilo, Wright, Tree, & Duchaine, 2015). Interestingly, one of these studies found that, instead of impaired visual word processing, almost all prosopagnosic subjects had difficulty perceiving the font or handwriting of text (Hills et al, 2015).…”

The Definition and Diagnosis of Developmental Prosopagnosia

“…The latter is perhaps unlikely, given the apparent cognitive heterogeneity in the presentation of DP, implying that the condition may have different subtypes and result from a potentially large variation of genetic and/or developmental atypicalities (Bate & Bennetts, 2014). Given the possibility that even apparent familial cases may not necessarily reflect genetic influence, other authors prefer to use the more conservative term "DP" for all cases of prosopagnosia with an absence of brain injury (e.g., Duchaine et al, 2007;Susilo & Duchaine, 2013;Susilo, Wright, Tree, & Duchaine, 2015).…”