Estimation by humans of signals simulating different sound movement directions and specificity of the perception of these signals by patients with temporal epilepsy

The perception of moving sound stimuli that imitate directional sound source movement was studied in healthy subjects and in patients with temporal lobe lesions, as well as in a group of patients with simultaneous lesions of the temporal cortex and hippocampus. Under the conditions of dichotic stimulation of patients with the rightor left-side foci of convulsive activity, the nature and length of the trajectories of the emerging subjective sound images (SSI) were estimated depending on the direction of movement and interaural time difference (700, 400, 200 μs). The audiograms of all patients did not differ from those of healthy subjects, suggesting that the auditory sensitivity of patients remained unimpaired. However, in the patients, the trajectories were shorter than the trajectories in healthy subjects at all the values of the initial time delay and at all the directions of SSI movements. In patients with the cortical temporal epilepsy, changes of the subjective sound field were the most significant in the case of the right-side localization of foci of the convulsive activity. In patients with simultaneous lesions of the temporal cortex and hippocampus, the averaged trajectories of SSI movement differed significantly from those in the group of healthy subjects (p < 0.01) and in patients with a relatively isolated lesion of the temporal cortex (p < 0.05); these trajectories were independent of the initial delay. The mediobasal structures of the temporal lobe that are involved in the epileptic process proved to play a significant role in the perception and estimation of the moving sound stimuli, although they do not belong to the auditory system proper. The possible mechanisms underlying disorders in patients with temporal epilepsy are discussed.