Acoustic-induced eye movements.

ABSTRACT

This article reports the influence of moving acoustic signals on eye movements (oculomotor functions) using 350 healthy test subjects. An acoustic test setting developed especially for this purpose has made possible the application of moving acoustic signals of varying frequency and form (square stimuli, sinusoidal stimuli, circular movements), as well as the examination of visual-acoustic and vestibular-acoustic interactions. It must be stressed that according to these investigations, both voluntary and involuntary eye movements can be demonstrated in response to moving acoustic signals. Involuntary eye movements, however, under th given experimental conditions, only are observed in about 20% of all test subjects and their frequency of occurrence is highest in young female subjects. They are most pronounced in darkness and when there is no fixation, and they can be coupled to varying degrees with the given acoustic signal. Voluntary and involuntary eye movements do not differ very much from one another. They consist mainly of a series of saccades that form staircase jerks. In both cases, no typical smooth movements or nystagmoid movement forms occur--which are predominant in tracking eye movements of visual stimuli. Occasionally, slight drifting movements can be demonstrated in the intersaccadic intervals. At a larger movement amplitude and increased movement frequency of the sound signal, pure opposite jerks finally appear, which follow up to a movement frequency of 1 Hz. The eye movements are influenced only slightly by a change in the amplitude of the sound movement (+/- 15 degrees to +/- 90 degrees). However, a close phase relationship between eye and sound movement exists. If instead of continuous acoustic signals (music), single burst signals are given at an increasing repetition rate, this results (at low repetition rates of bursts) in orienting reactions upon the individual signals, while at high signal repetition rates (above 0.5 Hz), continuous eye movements in the form of staircase jerks result. In investigating acoustically induced tracking eye movements, many new questions have arisen that previously have been open only to psychophysical studies.