The Journal of Neurophysiology Vol. 84 No. 1 July 2000, pp. 96-101
Copyright ©2000 by the American Physiological Society

Saccades to Sounds: Effects of Tracking Illusory Visual Stimuli

 ¹Department of Neurology,  ²Department of Biomedical Engineering, and  ³Department of Neuroscience, Department of Veterans Affairs Medical Center and University Hospitals, Case Western Reserve University, Cleveland, Ohio 44106

Somers, Jeffrey T., Vallabh E. Das, Louis F. Dell'Osso, and R. John Leigh. Saccades to Sounds: Effects of Tracking Illusory Visual Stimuli. J. Neurophysiol. 84: 96-101, 2000. In 10 normal human subjects, we studied the accuracy of memory-guided saccades made to the remembered locations of visual targets and sounds. During the time of stimulus presentation, subjects were smoothly tracking a projected laser spot that was moving horizontally across a tangent screen, sinusoidally ±15° at 0.25 Hz. In one set of experiments, the laser spot moved across a 40° × 28° random dot display that moved synchronously in the vertical plane; this induced a strong illusion that the trajectory of the laser spot was diagonal (variant of Duncker illusion). In control experiments, the laser spot moved across the same display, which was stationary. The visual targets and speakers were at six locations (range ±15°) in the horizontal plane. Saccades made to the remembered locations of targets presented during background motion (illusion) were significantly (P < 0.05) more inaccurate than with the background stationary (control) in 9 of 10 subjects for lights and in 6 of 10 subjects for sounds. As a group, the median change in errors due to the Duncker illusion was ~2.5 times greater for visual compared with acoustic targets (P < 0.001). These findings are consistent with electrophysiological studies which have shown that neurons in the primate lateral intraparietal area (LIP) may respond to both visual and auditory targets and these neurons are also influenced by the Duncker illusion during programming of memory-guided saccades.