The more you know the less you can tell: inhibitory effects of visuo-semantic activation on modality specific visual misnaming

Associative (prosop)agnosia without (apparent) perceptual deficits: A case-study

In associative agnosia early perceptual processing of faces or objects are considered to be intact, while the ability to access stored semantic information about the individual face or object is impaired. Recent claims, however, have asserted that associative agnosia is also characterized by deficits at the perceptual level, which are too subtle to be detected by current neuropsychological tests. Thus, the impaired identification of famous faces or common objects in associative agnosia stems from difficulties in extracting the minute perceptual details required to identify a face or an object. In the present study, we report the case of a patient DBO with a left occipital infarct, who shows impaired object and famous face recognition. Despite his disability, he exhibits a face inversion effect, and is able to select a famous face from among non-famous distractors. In addition, his performance is normal in an immediate and delayed recognition memory for faces, whose external features were deleted. His deficits in face recognition are apparent only when he is required to name a famous face, or select two faces from among a triad of famous figures based on their semantic relationships (a task which does not require access to names). The nature of his deficits in object perception and recognition are similar to his impairments in the face domain. This pattern of behavior supports the notion that apperceptive and associative agnosia reflect distinct and dissociated deficits, which result from damage to different stages of the face and object recognition process.

A metanalysis of impaired and spared naming for different categories of knowledge in patients with a visuo-verbal disconnection

The study of the neuroanatomical correlates of category-specific semantic disorders has strongly supported the 'sensory/motor model of semantic knowledge,' which assumes that the cortical areas that have critically contributed to the development of various categories are also implicated in their semantic representation. However, if the anatomo-clinical correlates are consistent with the model, less clearcut results have been obtained by functional neuroimaging experiments. In the present metanalysis, I addressed the question from a different viewpoint, shifting attention from the anatomical lesion in patients with category-specific semantic disorders to the pattern of naming impairment shown by patients suffering from a disconnection between visual areas and lexical output mechanisms. According to the model, living entities should be particularly impaired, since their semantic representations are mainly based upon visual perceptual attributes. On the contrary, actions and body parts (and to a lesser extent artefacts) should be relatively spared, as their semantic representations are mainly based upon motor, somato-sensory or functional attributes. These predictions were checked by reviewing the categorical pattern of naming impairment shown by patients with a visuo-verbal disconnection and a category-specific naming impairment published in the last 20 years. The pattern of impaired and spared categories observed in these patients was consistent with the hypothesis, since: (1) 'actions' and 'body parts' were systematically spared in comparison to all the other categories; (2) 'artefacts' were relatively spared with respect to the 'living categories'; and (3) within the biological categories, 'plants' were usually more impaired than animals.