Short-Latency, Goal-Directed Movements of the Pinnae to Sounds That Produce Auditory Spatial Illusions

1 Department of Physiology and 3 Neuroscience Training Program, University of Wisconsin, Madison, Wisconsin; and 2 Department of Physiology and Biophysics, University of Colorado Health Sciences Center, Aurora, Colorado Submitted 25 August 2009; accepted in final form 31 October 2009 ABSTRACT The precedence effect (PE) is an auditory spatial illusion whereby two identical sounds presented from two separate locations with a delay between them are perceived as a fused single sound source whose position depends on the value of the delay. By training cats using operant conditioning to look at sound sources, we have previously shown that cats experience the PE similarly to humans. For delays less than ±400 µs, cats exhibit summing localization, the perception of a "phantom" sound located between the sources. Consistent with localization dominance, for delays from 400 µs to 10 ms, cats orient toward the leading source location only, with little influence of the lagging source. Finally, echo threshold was reached for delays >10 ms, where cats first began to orient to the lagging source. It has been hypothesized by some that the neural mechanisms that produce facets of the PE, such as localization dominance and echo threshold, must likely occur at cortical levels. To test this hypothesis, we measured both pinnae position, which were not under any behavioral constraint, and eye position in cats and found that the pinnae orientations to stimuli that produce each of the three phases of the PE illusion was similar to the gaze responses. Although both eye and pinnae movements behaved in a manner that reflected the PE, because the pinnae moved with strikingly short latencies ( 30 ms), these data suggest a subcortical basis for the PE and that the cortex is not likely to be directly involved. Address for reprint requests and other correspondence: D. J. Tollin, Univ. of Colorado Health Sciences Ctr., Dept. of Physiology and Biophysics, Mail Stop 8307, PO Box 6511, Aurora, CO 80045 (E-mail: Daniel.Tollin{at}UCDenver.edu ).