Differential thresholds for tempi (with interonset intervals ranging from 100 to 1,500 msec) were measured using an adaptive 2IFC paradigm for several types of auditory sequences. In Experiment 1, the number of intervals in an isochronous sequence was varied to compare the sensitivity for single intervals with that for sequences oftwo to six intervals. Mean relative just noticeable differences (JNDs) decreased as the number of intervals increased (single intervals = 6%, two intervals = 4%, four intervals = 3.2%, six intervals = 3%) and were optimal at intermediate tempi for both sequences and single intervals (as low as 1.5% in the range between 300 and 800 msec), In Experiment 2, the sensitivity for different types of irregular sequences was studied. Globally, JNDs for irregular sequences were of an intermediate level between that observed for single intervals and that observed for regular sequences. However, the closer a sequence was to regularity, the lower its relative JND. Experiment 3 demonstrated that musicians were more sensitive than nonmusicians to changes in tempo, and this was true for single intervals and for regular and irregular sequences, demonstrating the role of training on these abilities. The results are discussed in terms of possible underlying mechanisms, in particular those providing a mental representation of the mean and dispersion of successive interval durations.How small a change in duration are we able to detect? The psychoacousticalliterature on time perception suggests that when subjects are asked to compare two intervals (empty or filled by a sound) they are able to say which is longer or shorter when there is a difference of at least 6% to 10% of the standard duration (Abel, 1972;Allen, 1979;Creelman, 1962;Getty, 1975Getty, , 1976Small & Campbell, 1962;Woodrow, 1951). This is true within a range of 200-2,000 msec, and the actual precision depends on many different factors, in particular the method used and the physical characteristics of the events marking the intervals. A similar level of sensitivity is also found when subjects are asked to detect a change in duration of one or two of the intervals contained in regular and rhythmic sequences (Drake, 1990(Drake, , 1992(Drake, , 1993 Drake, Botte, & Gerard, 1989; Drake, Gerard, & Botte, in press;Halpern & Darwin, 1982;Hirsh, Monahan, Grant, & Singh, 1990; van Noorden, 1975). However, when subjects are asked to compare the rate or tempo of two isochronous sequences, the little data available suggests that subjects are much more sensitive to changes, since they are able to detect a change of about 2% (Michon, 1964).How can we explain this greater sensitivity to changes in tempo of sequences than to changes in duration of single intervals? An obvious answer is that in the case of We wish to thank Professors Douglas Creelman, Ken Grant. and Peter Killeen for their helpful reviews and Mari Jones, Jean Lorenceau, and Steve McAdams for their comments on previous versions of this manuscript. Correspondence should be addressed to C. Drak...

Previous findings on streaming are generalized to sequences composed of more than 2 subsequences. A new paradigm identified whether listeners perceive complex sequences as a single unit (integrative listening) or segregate them into 2 (or more) perceptual units (stream segregation). Listeners heard 2 complex sequences, each composed of 1, 2, 3, or 4 subsequences. Their task was to detect a temporal irregularity within 1 subsequence. In Experiment 1, the smallest frequency separation under which listeners were able to focus on 1 subsequence was unaffected by the number of co-occurring subsequences; nonfocused sounds were not perceptually organized into streams. In Experiment 2, detection improved progressively, not abruptly, as the frequency separation between subsequences increased from 0.25 to 6 auditory filters. The authors propose a model of perceptual organization of complex auditory sequences.

This study investigated the relations between theoretical auditory filters and "attentional filters" observed when measuring the detectability in noise of tones of expected or unexpected (probe) frequency. The effect of the level of the noise and the frequency range (narrow or wide) of the probes was assessed. For each 2IFC trial, a tone of the expected target frequency was presented as a cue preceding the two observation intervals--the signal was more often the expected than an unexpected frequency. For the narrow frequency range of probe frequencies, increasing the masker level resulted in a broadening of the probe-signal contour (percent correct as a function of probe frequency); however, detection was significantly better only for probe frequencies farthest from the target frequency. For the wide range of probe frequencies, the percentage of correct detections depended less systematically on masker level; however, detection was better and the attentional band wider than in the narrow frequency range. The results suggest that attentional focusing does not simply reflect auditory filtering: A more central and adaptive process may operate from the outputs of adjacent or more distant auditory filters.