Neuromagnetic study of pattern recognition activity in the human brain

According to human patient studies [1], the lesion in the inferior temporal cortex and/or in the parietal areas causes the agnosia. There are two types of agnosia; apperceptive agnosia and association agnosia. According to Farah [2], the apperceptive agnosia patients seem to have adequate elementary visual functions and general cognitive ability, but they were dramatically impaired on the simplest forms of shape discrimination. On the other hand, the associative agnosia patients have a selective impairment in recognizing visually presented objects despite apparently adequate visual perception. However, Farah [2] carefully investigated the conventional apperceptive agnosia patients and found that the simultanagnosia patients, simultanagnosics, had been included in this apperceptive agnosia group because the disturbance of this simultanagnosia was very similar to the conventional apperceptive agnosia. The simultanagnosics cannot see or recognize more than one object. Farah claimed that there are two types of simultanagnosia [2]; dorsal and ventral simultanagnosia. The dorsal simultanagnosics, having damage in the bilateral occipitoparietal regions, cannot see more than one object. In contrast, the ventral simultanagnosics, having left inferior occipitotemporal damage, can see more than one object, but cannot recognize more than one object. Therefore, when recognizing more than one object, both the occipitotemporal and the occipitoparietal regions may be activated.