Dissociation of visual and auditory order thresholds after cerebral injury in man

Visual and auditory order thresholds were measured with aphasic patients suffering from lesions of the left hemisphere, non-aphasic patients with lesions of the right hemisphere, and a control-group of normals. The aphasic patients showed the highest auditory order thresholds. Visual order thresholds were equal for both groups of patients, but significantly increased compared to those of the control-group. It seems that a lesion of the left hemisphere has consequences for temporal signal processing. The impairment affects primarily the auditory modality. This finding perhaps explains certain difficulties of aphasic patients on the phonetic level.