Auditory apparent motion in the free field: The effects of stimulus duration and separation

Abstract

The effects of stimulus duration and spatial separation on the illusion of apparent motion in the auditory modality were examined. Two narrow-band noise sources (40 dB, A-weighted) were presented through speakers separated in space by 2.5°, 5°, or 10°, centered about the subject's midline. The duration of each stimulus was 5, 10, or 50 msec. On each trial, the sound pair was temporally separated by 1 of 10 interstimulus onset intervals aSOIs): 0, 2, 4, 6, 8, 10, 15, 20, 50, or 70 msee. Five subjects were tested in nine trial blocks; each block represented a particular spatial-separation-duration combination. Within a trial block, each ISOI was presented 30 times each, in random order. Subjects were instructed to listen to the stimulus sequence and classify their perception of the sound into one of five categories: single sound, simultaneous sounds, continuous motion, broken motion, or successive sounds. Each subject was also required to identify the location of the first-occurring stimulus (left or right). The percentage of continuous-motion responses was significantly affected by the ISOI [F(9,36) = 5.67, p < .001], the duration x ISOI interaction [F(18,72) = 3.54, p < .0001], and the separation x duration x ISOI interaction [F(36,144) The results indicate that a minimum duration is required for the perception of auditory apparent motion. Little or no motion was reported at durations of 10 msee or less. At a duration of 50 msec, motion was reported most often for ISOIs of 20-50 msee. The effect of separation appeared to be limited to durations and ISOIs during which little motion was perceived.The illusion of apparent motion is a general sensory phenomenon, because it occurs in the visual, auditory, and tactual modalities. Visual apparent motion has been studied extensively, and it is probably the dominant means of investigating visual motion perception. On the other hand, the illusion of auditory apparent motion has received only minimal attention in the literature. In such work, the auditory illusion has usually been compared with the visual illusion.The search for similarities between these illusions has focused on the applicability of Korte's laws (Kolers, 1972;Korte, 1915) to the auditory illusion. Korte determined the relationship between the duration of the stimulus, the interstimulus interval (or interstimulus onset interval, ISO!), the spatial separation between the stimuli, and the intensity of the stimuli. Two of these laws (the second and third) have been studied in the auditory modality. Korte's (1915) second law describes the relationship between the ISOI and duration. This law states that for visual apparent motion to be maintained, when the duration of the stimuli is increased, the ISOI must also increase, butCorrespondence should be addressed to T. Z. Strybel, Department of Psychology, California State University, Long Beach, CA 90840.the ISOI increases at a slower rate. This law was verified in the visual modality by Neuhaus (1930), and it is described in Kolers (1972). For a duration of ...

The effect of timing and spatial separation on the velocity of auditory apparent motion

“…AAM can be heard at the same burst duration-SOA combinations for separations between 3°and 160°, under monaural and binaurallistening conditions and for sources separated in the horizontal and midsaggital planes (Strybel, Manligas, Chan, & Perrott, 1990;Strybel & Neale, 1994;Strybel, Witty, & Perrott, 1992). In fact, motion can be heard when the lead and lag stimulus are presented from a single loudspeaker (Strybel, 1994;Perrott & Strybel, 1997).…”

“…The detection of AAM is affected by burst duration and SOA, however. The minimum burst duration for the illusion is roughly 25 msec (Strybel & Neale, 1994;Strybel et al 1992), and the SOAs that produce AAM increase with burst duration, according to Korte's second law ofvisual apparent motion (Briggs & Perrott, 1972;Strybel & Neale, 1994). Although only stimulus timing affects the minimum conditions for motion, both spatial and temporal factors affect discrimination ofthe direction ofmotion.…”

Effect of Velocity and Time-Step on the Continuity of a Discrete Moving Sound Image

“…Whether the listener can perceive the discrete motion as continuous or not is dependent on conditions such as the spatial separation of sounds, stimulus duration, moving velocity, or time-step (time period of the discrete motion) of the discrete process. Strybel et al [8] investigated the effects of stimulus duration and spatial separation of two sounds that were displayed through two loudspeakers in a free field alternately. Lakatos [9] also reported that their results indicated a direct 2 Advances in Acoustics and Vibration relationship between the horizontal separation of two sounds and the critical stimulus onset asynchrony (SOA).…”

Upper threshold of burst duration for continuous apparent motion. Effects of amplitude modulation and frequency band.

“…The range of burst duration and the ISOI for auditory apparent motion is not sensitive to the location and the spatial interval of stimuli (Nakajima et al, 1990 ;Strybel et al, 1990 ;Strybel et al, 1992 ;Strybel 1993 ;Mizushima et al, 1994), unlike that for visual apparent motion (Korte, 1915 ;Scholz, 1924 ;etc.). The timing condition for auditory continuous motion is also independent of whether monaural listening or binaural listening is used (Strybel and Neale, 1994).…”

“…Based on the relationship between the burst duration and the ISOI, Briggs and Perrott (1972) classified the perception under dichotic listening into five categories : single sound, simultaneous sounds, continuous motion, broken motion, and successive sounds. Strybel et al (1989Strybel et al ( , 1990Strybel et al ( and 1992) also investigated the relationship between the category and the timing under binaural and monaural conditions in a free field. They replicated the results obtained by Briggs and Perrott (1972).…”