Temporal-order discrimination in nonspeech sequences presented to the left or the right ear

Abstract

Three right-handed, naive listeners with normal hearing had to discriminate between two nonspeech sequences consisting of four pure tones that differed only in the temporal order of the two middle tones (HMLH and HLMH). The frequencies of the tonal components were fixed at 1.4 (H), 1 (M), and 0.7 (L) kHz. The sequences were presented at 76 dB SPL, randomly to either the left or the right ear of the subjects at either of two durations. For each subject ear and for each daily half-session, two-point psychometric functions were constructed and threshold durations were estimated, with the 75% correct performance taken as the threshold. These threshold estimates show that (1) untrained observers need 100–240 msec/tonal component in order to discriminate the temporal order of two short tonal sequences; (2) this threshold value rapidly decreases and reaches an asymptotic duration of 10–20 msec/component around the eighth day of sessionS; (3) contrary to several reports on similar experiments using speech or speechlike stimuli, these threshold estimates indicate that there is no difference in temporal-order discrimination of sequences presented to the left or the right ear. [Supported by NINDS Grant No. 03856.]