Gary R. Kidd
Dept. of Speech and Hear. Sci., Indiana Univ., Bloomington, IN 47405
Thresholds for detection and frequency discrimination were determined for tones that occurred at unexpected temporal locations within 12-tone sequences. Expectancies were established by repeated presentations of a standard pattern on each trial. Temporal deviations were introduced in comparison patterns by advancing or delaying the onset of a single ``target'' tone while maintaining its serial position within the pattern. Rhythmic patterns consisting of 350- and 150-ms intertone intervals were used to allow for a large range of temporal displacements. Thresholds were determined for target tones that were advanced (``early'' targets) or delayed (``late'' targets) by various degrees. Thresholds for displaced targets were elevated with respect to nondisplaced targets for both detection and discrimination. However, for most listeners, there was little or no effect of temporal displacement on detection except when targets were advanced by 200 ms or more. Temporal deviations had more consistent effects on frequency discrimination for both early and late targets. The results are consistent with the view that, when presented with an auditory pattern, a listener's attention is dynamically allocated in time in response to the temporal structure of the pattern. [Work supported by NIH.]