Frequency-specific, location-nonspecific adaptation of interaural time difference sensitivity

Abstract

Human listeners' sensitivity to interaural time differences (ITD) was assessed for 1000 Hz tone bursts (500 ms duration) preceded by trains of 500-ms "adapter" tone bursts (7 s total adapter duration, frequencies of 200, 665, 1000, or 1400 Hz) carrying random ITD, or by an equal-duration period of silence. Presentation of the adapter burst train reduced ITD sensitivity in a frequency-specific manner. The observed effect differs from previously described forms of location-specific psychophysical adaptation, as it was produced using a binaurally diffuse sequence of tone bursts (i.e., a location-nonspecific adapter stimulus). Results are discussed in the context of pre-binaural adaptation.

Figure 1

Schematic illustration of example stimuli. Each trial consisted of a 7 s adapter interval followed by a 500 ms pause and a 1.1 s test interval (see text). Here, “No Adapter” and “1000 Hz Adapter” conditions are illustrated. The subject s task was to indicate whether the final 1000 Hz tone burst was shifted to the left or right of the preceding 1000 Hz diotic reference tone burst.

Figure 2

ITD discrimination thresholds as a function of adapter condition. Dashed lines and symbols plot individual subjects mean thresholds based on 10 threshold estimates for each condition, with error bars giving ±1 standard error of the mean across runs. The solid line and symbols plot the cross-subject mean thresholds for each condition with error bars giving ±1 standard error of the mean across subjects. Individual subject data are offset along the abscissa for clarity. Only subjects 0502 and 0601 completed the 1400 Hz Adapter condition; thus a mean is not displayed for that condition.