The Effects of Age on Saccades made to Visual, Auditory and Tactile Stimuli

Anthony Sullivan B.Orth (Hons), D.O.B.A.
Larry A Abel, PhD
School of Orthoptics, La Trobe University, Melbourne, Australia

Purpose: To investigate the effects of stimulus modality and aging on saccades in healthy human subjects.
Methods: Visual, auditory and tactile evoked saccades of young, middle aged and older healthy subjects with normal visual function, hearing and somatosensation were measured and analysed. The young group was comprised 12 subjects aged between 20 and 30 years of age, with a mean age of 23.7 (+ 2.9) years. The middle-aged group was comprised of 7 subjects ranging in age from 40 to 50 years with a mean age of 46.9 + 3.4 years. The older group was comprised of 7 subjects ranging from 60 to 70 years of age, with a mean age of 63.86 +3.0 years. The visual stimuli were presented by light emitting diodes at 0, +5, 10, 15 and 19 degrees. The auditory stimuli were noise-emitting loudspeakers placed above the visual stimuli. The tactile stimuli were presented by bone vibrators driven at 250 Hz placed beneath the fingertips at corresponding angles.
Results: The latency of auditory saccades was significantly longer than tactile saccades, whose latencies were in turn significantly greater than visual saccades. Visual saccades were most accurate and least variable, followed by tactile saccades. Auditory saccades were found to be highly variable and grossly inaccurate. Age did not affect saccades to different sensory modalities.
Conclusions: The results suggest that non-visual stimuli undergo greater neural transformation than visual stimuli, and, specifically, auditory stimuli undergo more neural transformation than tactile stimuli for the generation of a saccade. The findings of this study provide the initial basis for eventual clinical applications of tactile stimuli in the evaluation and rehabilitation of persons with visual impairment.