William Morris Hartmann
Dept. of Phys., Michigan State Univ., East Lansing, MI 48824
Brad Rakerd
Michigan State Univ., East Lansing, MI 48824
In a sagittal plane localization experiment, listeners (N=8) were required to localize a train of eight clicks that originated from a source that was either directly in front, overhead, or behind. Click trains were made from 25-(mu)s pulses, separated by 110 ms, and were presented in an anechoic room. The principal experimental parameter was the peak level of the clicks: 68, 74, 80, 86, 92, or 98 dB SPL. All listeners except one showed a level disadvantage: The localization error rate increased with increasing level, on the average by a factor of 10 over the range of levels. It was conjectured that the level disadvantage arises from a failure of the auditory system to resolve details of the spectral shaping caused by pinna, head, and upper torso in the case of a high-level pulse. Resolving these details is necessary for localization in the sagittal plane. This conjecture was tested in headphone experiments on filtered click discrimination. Many instances of level disadvantage were found, but none so strong or consistent as the original localization effect. [Work supported by the NIDCD, DC00181.]