THE PROPORTION-OF-THE-TOTAL-DURATION RULE FOR THE DISCRIMINATION OF AUDITORY PATTERNS

A principle of auditory perception that governs the detectability of changes in components in unfamiliar sequences of tones is demonstrated in four experiments. The proportion-of-the-total-duration (PTD) rule can be stated as follows: Each individual component of an unfamiliar sequence of tones is resolved with an accuracy that is a function of its proportion of the total duration of the sequence or "pattern." An adaptive-tracking frequency-discrimination task was used in all experiments. Experiment 1 demonstrated that the PTD rule holds over a wide range of total pattern durations, numbers of components, and component durations. Experiment 2 demonstrated that the PTD rule governs discrimination performance despite variation in the relative durations of context and target tones. Experiment 3, using a variable temporal position for the target, confirmed that the PTD effect does not require that a listener be able to anticipate the temporal location of the target tone. Experiment 4, using two target tones, showed that the PTD rule applies to the proportional duration of individual components within patterns and not to the total proportional duration of nonadjacent components within the pattern. These findings are incompatible with performance limitations based on a fixed-duration short-term memory capacity and with versions of informational limitations in which the amount of information in a pattern varies either with the number of components or with the total pattern duration. The PTD rule appears to reflect the way listeners distribute their attention when presented with unfamiliar complex sounds that have no structural properties (other than proportional duration) that significantly increase the salience of individual components.