Biomedical subjects

M Behrmann

Publications and source records attributed to M Behrmann.

12 recordsLinked to original sources

PubMed1992

Dissociation between mental imagery and object recognition in a brain-damaged patient.

Visual imagery is the creation of mental representations that share many features with veridical visual percepts. Studies of normal and brain-damaged people reinforce the view that visual imagery and visual perception are mediated by a common neural substrate and activate the same representations. Thus, brain-damaged patients with intact vision who have an impairment in perception should have impaired visual imagery. Here we present evidence to the contrary from a patient with severely impaired object recognition (visual object agnosia) but with normal mental imagery. He draws objects in considerable detail from memory and uses information derived from mental images in a variety of tasks. In contrast, he cannot identify visually presented objects, even those he has drawn himself. He has normal visual acuity and intact perception of equally complex material in other domains. We conclude that rich internal representations can be activated to support visual imagery even when they cannot support visually mediated perception of objects.

Adult↗

PubMed1990

The evolution of pure alexia: a longitudinal study of recovery.

This case report documents the partial recovery, over a 12-month period, of pure alexia in an adult female following a left occipital infarction. Measures of speed and accuracy were obtained on an oral reading and a lexical decision task immediately postonset and then on 10 subsequent occasions. Explicit letter-by-letter reading was observed only during the first week poststroke but a significant effect of word length was seen in all testing sessions. Reading accuracy was relatively good at all stages and reading latency showed a remarkable decrease over time but did not reach normal reading rates. The inability to use higher-order orthographic knowledge, as manifest in the absence of a word superiority effect, was still noted at one year postonset. We therefore concluded that the change in behavior was attributable to increased proficiency in the use of the adaptive letter-by-letter procedure rather than to the resolution of the underlying deficit. It is suggested that longitudinal neurobehavioral studies add to our understanding of the alexic deficit and provide insight into the recovery process.

Adult↗

PubMed1990

Perceptual and conceptual mechanisms in neglect dyslexia. Two contrasting case studies.

The contribution of peripheral, data-driven effects is contrasted with conceptual, 'top-down' effects to the reading performance of 2 subjects with neglect dyslexia following a single right hemisphere lesion. Several tasks were administered, manipulating the physical, lexical or morphemic properties of the stimuli in an attempt to establish whether the attentional deficit disrupts reading at an early or late stage of processing. Both subjects were impaired at detecting elementary stimulus features on the left side of the display but were even more impaired at identifying conjoined features. One subject's performance was influenced by structural manipulations which altered the low-level representation of the stimulus. The other was less affected by structural changes of the stimuli but was influenced by the lexical and morphemic status of the words. This apparent double dissociation is interpreted as arising from a graded attentional deficit at a single locus, early in the reading process where low-level information is detected. When the deficit is not severe sufficient information may be picked up and may interact with higher order lexical knowledge to offset partially the peripheral malfunction. For a severe attentional deficit, top-down knowledge is not engaged as insufficient information is processed on the left-hand side. This hybrid view of attention provides insight into the mechanisms underlying neglect dyslexia and bears on the role of attention in normal visual processing.

Aged↗

PubMed1989

Category-specific treatment of a lexical-semantic deficit: a single case study of global aphasia.

The aim of this study was to improve the comprehension of single items in a subject with global aphasia. Existing models of semantic organisation were used to inform and guide the treatment programme. Detailed pre-therapy testing suggested a severe comprehension deficit with an inability to obtain a precise semantic specification of the items, irrespective of modality of input. A category-specific hierarchical treatment programme including generic and specific details about items was implemented through various exercises and drills. Post-therapy testing revealed a significant improvement on treated and untreated items of treated categories but limited generalisation to items in untreated categories. Improvement in the subject's general semantic abilities was also documented following treatment. The results, which are shown to be a direct consequence of the intervention programme, lend support to the categorical and hierarchical view of the organisation of semantics and provide a basis for future rehabilitation studies in this area.

Aphasia↗

PubMed1987