Motion aftereffects with horizontally moving sound sources in the free field

Abstract

A horizontally moving BOund was presented to an observer seated in the center of an anechoic chamber. The BOund, either a 500-Hz low-pass noise or a 6300-Hz high-pass noise, repeatedly traversed a semicircular arc in the observer's front hemifield at ear level (distance: 1.5 m), At lO-sec intervals this adaptor was interrupted, and a 750-msec moving probe (a 500-Hz low-pass noise) was presented from a horizontal arc 1.6 m in front of the observer. During a run, the adaptor was presented at a constant velocity (-200°to +200 0/sec), while probes with velocities varying from -10°to +10 0/sec were presented in a random order. Observers judged the direction of motion (left or right) of each probe. As in the case of stimuli presented over headphones (Grantham & Wightman, 1979),an auditory motion aftereffect (MAE) occurred: subjects responded "left" to probes more often when the adaptor moved right than when it moved left. When the adaptor and probe were spectrally the same, the MAE was greater than when they were from different spectral regions; the magnitude of this difference depended on adaptor speed and was subjectdependent. It is proposed that there are two components underlying the auditory MAE: (1) a generalized bias to respond that probes move in the direction opposite to that of the adaptor, independent of their spectra; and (2) a loss ofsensitivity to the velocity of moving BOunds after prolonged exposure to moving BOunds having the same spectral content.We have reported the existence of an auditory motion aftereffect (MAE), analogous to the well-known waterfall effect in vision (Grantham & Wightman, 1979). In the previous study, we exposed subjects to sounds that moved repeatedly through the head in one direction (created by dynamically varying the interaural time differences and interaural level differences of pure tones presented over headphones). Following such exposure, subjects tended to respond that subsequently presented probes moved in the opposite direction. This tendency indicates that an auditory MAE exists, although whether the effect is a sensory one or simply a response bias is not yet clear.The visual MAE is almost certainly a sensory effect. A generally accepted theory to account for this effect postulates the existence of directionally sensitive analyzers in the visual system (Sekuler & Pantle, 1967). These analyzers become fatigued from prolonged stimulation by a pattern moving in their preferred direction; subsequently, upon presentation of a neutral (stationary) pattern, activity in the analyzers tuned to the opposite direction dominates, resulting in the perception of movement when none is present. The fact that single units that respond selectively to the direction of a moving target have been found in the eat's cortex (Hubel & Wiesel, 1962)

Processing Temporal Modulations in Binaural and Monaural Auditory Stimuli by Neurons in the Inferior Colliculus and Auditory Cortex

“…However, the presence of neurons that are sensitive to each direction may provide a basis for the motion after-effects that occur after conditioning for extended periods with one direction of motion (Grantham 1989;Carlile et al 2001). That is, movement in one direction could lead to adaptation of neurons most sensitive to that particular direction, such that when the motion is stopped the activity in the non-adapted neurons will give a percept of motion in the opposite direction.…”

Distortions of perceived auditory and visual space following adaptation to motion

“…Early studies typically failed to demonstrate an effect that was both convincing and reliable between observers (e.g. Grantham and Wightman 1979;Grantham 1989;Reinhardt-Rutland 1992). In contrast, the results of recent studies provide more compelling evidence that a robust and replicable aMAE does indeed exist (Grantham 1998;Dong et al 2000;Jenison 2003, 2004).…”

Adaptation to auditory motion in the horizontal plane: Effect of prior exposure to motion on motion detectability

“…However, there were large intersubject differences in the shape of the MAMA versus adaptor velocity functions. This loss of sensitivity to motion that most subjects show after exposure to moving signals is probably one component underlying the auditory motion aftereffect (Grantham, 1989),in which judgments ofthe direction ofmoving sounds are biased in the direction opposite to that of a previously presented adaptor.…”

“…In the previous study (Grantham, 1989), the hypothesized loss of sensitivity to motion after exposure to moving signals was based on the shape of the psychometric This research was supported by NIH Grant DCOOI85. The author is grateful to Carl C. Crandell for assistance in data collection and analysis and to Maureen K. Powers for discussions about statistical procedures.…”

“…In a recent paper by Grantham (1989), the existence of an auditory motion aftereffect (MAE) was reported.…”