Detection of Dynamic Changes in Interaural Delay

The ability to detect a dynamic change in interaural time difference (ITD) was examined for rates of change from 3.125 to 32,000 s/s, for stimulus durations from 0.025 to 16 seconds, and for extent of change in interaural delay from 50 to 800 s. The stimulus was a sinusoidal tone of frequency f Hz presented to one ear and f f to the other ear, where f , the frequency difference, was varied to simulate different motion velocities. In a single-interval two-alternative forced-choice design, observers were required to discriminate between a stationary tone (same frequency to both ears) whose ITD was randomly selected between trials, and a tone with a dynamic interaural delay. Results showed that performance decayed at high and low velocities, although the specific cutoff velocities were dependent on distance traveled (i.e., total change in ITD). Higher velocity cutoffs were associated with greater distances. A minimum integration time of 100–400 ms was required for most observers before peak detection was reached. Stimulus durations greater than 4 seconds led to a decline in detection of movement, presumably due to a decay of trace memory and/or lapses in attention.