Unmasking of visual deficits following unilateral prestriate lesions in man.

The primate visual cortex is a mosaic of different areas which are roughly organized into two major pathways, a dorsal one along an occipito-parietal channel and a ventral one along an occipito-temporal channel. It is known that visual stimuli are processed differently within these two systems and one might expect therefore that behavioral deficits would differ according to the channel damaged by cerebral lesions. Two patients with left prestriate lesions presented perceptual deficits in the right visual field. These deficits involved reading, recognition of line drawings and colour perception and would be compatible with a dysfunction of the ventral system. Magnetic resonance imaging analysis confirmed that this was the case.

Lexicalization in an anomic patient.

Following a haemorrhage in the left temporal lobe, a 25 yr-old left-handed male patient presented a word finding difficulty, particularly in confrontation naming. The patient had extensive semantic knowledge of the items that he was not able to name. Several experiments showed that he had a poor phonological image of the target word and was poorly helped by phonological cues. He had a better knowledge of the graphological image, but it remained insufficient to result in word retrieval. On several occasions, when the patient failed to name a picture which happened to be lexicalized by a polysemous word, a residual covert word form could still operate as a link between different meanings of the target word; then, the patient produces a word or a circumlocution related to one meaning which was not the illustrated meaning. This kind of response could be called a parasemia. We postulate that the patient's deficit took place outside semantic treatment and before achievement of lexical (phonological or graphological) output.