The Role of Memory in Auditory Perception

Sound sources produce physical entities that, by definition, are extended in time. Moreover, whereas a visual stimulus lasting only 1 ms can provide very rich information, that is not the case for a 1-ms sound. Humans are indeed used to processing much longer acoustic entities. In view of this, it is natural to think that “memory” (in the broadest sense) must play a crucial role in the processing of information provided by sound sources. However, a stronger point can be made: It is reasonable to state that, at least in the auditory domain, “perception” and “memory” are so deeply interrelated that there is no definite boundary between them. Such a view is supported by numerous empirical facts and simple logical considerations. Consider, as a preliminary example, the perception of loudness. The loudness of a short sound, e.g., a burst of white noise, depends on its duration (Scharf 1978). Successive noise bursts equated in acoustic power and increasing in duration from, say, 5 ms to about 200 ms are perceived not only as longer and longer but also as louder and louder. Loudness is thus determined by a temporal integration of acoustic power. This temporal integration implies that a “percept” of loudness is in fact the content of an auditory memory. A commonsense notion is that memory is a consequence of perception and cannot be a cause of it. In the case of loudness, however, perception appears to be a consequence of memory. This is not a special case: Many other examples of such a relationship between perception and memory can be given. Consider, once more, the perception of white noise. A long sample of white noise, i.e., a completely random signal, is perceived as a static “shhhhh...” in which no event or feature is discernible. But if a 500-ms or 1-s excerpt of the same noise is taken at random and cyclically repeated, the new sound obtained is rapidly perceived as quite different. What is soon heard is a repeating sound pattern filled with perceptual events such as “clanks” and “rasping” (Guttman and Julesz 1963; Warren 1982, Chapter 3; Kaernbach 1993, 2004). It can be said that the perceptual events in question are a creation of memory, since they do not exist in the absence of repetitions. Kubovy and Howard (1976) provided another thought-provoking example. They constructed sequences of binaural “chords”