[Smooth pursuit eye movements evoked by head-phone acoustic stimulation]

Smooth pursuit eye movement evoked by binaural acoustic stimulation is examined in the present work. The effect of lateralization was achieved by modulating the interaural difference in intensity, within the headphone, following a pendular pattern. The test was performed on 10 healthy subjects; oscillation frequencies of the acoustic target being 0.15, 0.5 and 0.83 Hz, stimulus intensity 65 and 92 dB SPL. The acoustic signal consisted of white noise. Each trial was performed with eyes closed and then with eyes open. The results demonstrate that sinusoidal eye movement can only be obtained in a few subjects when the acoustic target has the lowest velocity and especially at the higher intensity. In all other cases eye movement was characterized by multiple saccades. The variability in eye movement amplitude is reduced and the value of this parameter decreases significantly under open-eye conditions. The data obtained are in agreement with other reports obtained with free field acoustic stimulation and demonstrate that smooth pursuit eye movement is principally an ocular reflex. In conclusion, acoustic smooth pursuit eye movement appears normally to be characterized by multiple saccades whose pattern can be modulated by intensity and oscillation frequency of the acoustic target as well as by the presence of visual inputs and attentional factors.