Discrimination of temporal jitter in patterned sequences of tones.

The perception of pure tone sequences in highly dependent on the serial pattern of tone frequencies. We propose that this phenomenon is mediated by a frequency-selective mechanism. Three models of the selective mechanism were evaluated in a temporal discrimination task. The observer was required to discriminate between two sequences of tone bursts. In one sequence the time interval between each tone burst was constant; in the other sequence the time interval was a random variable. A set of fixed and random pattern rules determined the frequency of each tone in the sequence. Discrimination performance was studied as a function of the magnitude of the time interval jitter and the serial pattern of tone frequency. Performance in the fixed pattern conditions was well described by a multiple-channel model in which timing information is available between tones within the same frequency region. The influence of higher order attentional factors was randomly determined. The frequency-selective mechanism appears to be sensitive to uncertainty about the frequency pattern of the input. Repeating the random pattern within each trial effectively eliminated this uncertainty. This result is consistent with experiments on the discrimination of word-length auditory patterns and temporal cues in speech.