Grantham [Grantham, J. Acoust. Soc. Am. 79, 1939-1949 (1986)] has proposed that subjects are able to resolve the velocity of a moving sound source simply by determining the distance traveled and the time required to complete the movement. In the current experiment, subjects were able to discriminate between accelerated and decelerated movements which were identical on both parameters; that is, the accelerated and decelerated movements began and ended at the same locus and required the same amount of time to be completed. The minimum duration required to discriminate between these two movement patterns was 310 and 90 ms, respectively, for displacements of 9 degrees and 18 degrees. These results suggest that, under some conditions, the perception of velocity in the auditory modality may be based upon something more than a simple comparison of the total distance traveled and the time required to complete the movement.

No abstract

The ‘‘snapshot’’ hypothesis [D. W. Grantham, J. Acoust. Soc. Am. 79, 1939–1949 (1986)] suggests that velocity is simply inferred. Subjects are assumed to be utilizing information regarding both the distance traveled from signal onset to offset and the temporal extent of the interval during which movement occurs. A number of motion patterns were examined in the current series of experiments with particular attention to whether subjects could discriminate between sequences in which both the distances traveled and the duration of the events were identical. As a case in point, subjects were able to discriminate between acceleration and deceleration movement patterns. The implications of these results will be discussed. [Work supported by NSF.]

Gilkey and Good [J. Acoust. Soc. Am. 92, 2334 (1992)] found that the detectability of a click-train signal, presented in the free-field, increased dramatically when the signal was spatially separated from a noise masker, in either azimuth or elevation. In separate conditions, stimuli were filtered into low-, mid-, and high-frequency regions. The pattern of results suggested that the increases in detectability might have been based on monaural, rather than binaural, processing. Here, this study was partially replicated using ‘‘virtual’’ sound sources. The stimuli were filtered through head-related transfer functions and presented through headphones. Binaural, left-ear monaural, and right-ear monaural stimulus presentations were compared. Thresholds in the binaural condition were in good agreement with the free-field data. Although there was evidence under some conditions of a small binaural advantage at low frequencies, in general, binaural performance was no better than monaural performance with the ‘‘better ear.’’ Overall, the results suggest that the subjects of Gilkey and Good could have performed as well as they did based on monaural processing alone. [Work supported by NIH-DC-00786 and AFOSR-91-0289.]

Previous research of moving sound sources show an increase of minimal displacements as a direct function of velocity. The current experiment attempted to establish upper limits for this function. Five subjects were tested, three naive and two experienced. MAMA thresholds for velocity ranging from 10 to 1500 deg per second were obtained using a three-up one-down adaptive procedure. For comparison purposes, visual targets were also employed in the paradigm. For velocities in excess of 100 deg per second, auditory displacement thresholds were substantially lower than those obtained for vision. However, the superiority of the visual modality was evident at lower rates of travel. These results will be discussed relative to our hypothesis that the auditory system may have a significant role in oculomotor processes.