So far we have been considering only pitch-related expectations. Listeners not only form expectations about what future events may occur, but also
when they occur. Caroline Palmer and Carol Krumhansl carried out a set of
probe-tone studies to determine when listeners most expect events to happen. Palmer and Krumhansl (1990) presented stimuli that created particular metric frameworks, like 4/4 and 3/4. Following a meter-defining
sequence, there was a pause, followed by a tone. Listeners were asked to judge the "goodness of fit" for each tone. Listeners assigned the highest values to those tones whose onsets coincided with the most important beats in the metric hierarchy, followed by the lesser beats, followed by the half-beat divisions, followed by tones that did not coincide with any beat. Mari Riess Jones has proposed that the metric hierarchy can be
understood as a structure for rhythmic attending. Auditory attention is directed at moments in time. That is, when listening, auditors do not pay attention equally at all moments. In rhythmic attending, Jones notes that the listener's attention is most acute at strong metric positions. That is, the metric hierarchy corresponds to a sort of temporal expectation
framework.
Consider the following experiment carried out by Jones, Moynihan,
MacKenzie and Puente (in press). Listeners heard an initial tone, followed by 12 "distractor" tones, followed by a comparison tone. The task of the experiment was for listeners to judge whether the comparison tone was higher or lower in pitch than the initial tone. In the following example, the first pitch (half-note B) is the initial tone, and the final pitch (half-note A#) is the comparison tone. The intervening tones are random distractor tones that increase the difficulty of the task.
Figure 18
Fig. 18. Typical stimulus used in Jones, Moynihan, MacKenzie & Puente (in press). Listeners heard a standard tone, followed by twelve interference tones, followed by a comparison tone.
Listeners were asked to judge whether the comparison tone is higher or lower than the standard tone. The temporal position of the comparison tone was varied so that it would occur earlier or later than expected. See also Fig. 19.
Jones et al manipulated the precise temporal position of the final
comparison tone. In some trials, the onset of the tone coincided with the precise downbeat (position 3). Other trials were slightly ahead (position 2) or slightly delayed (position 4) compared to the downbeat. Yet other trials were considerable ahead (position 1) or delayed (position 5) compared to the downbeat. Jones et al found that the accuracy of pitch-comparison judgments depended on the precise temporal placement of the
the comparison tone coincided with the presumed downbeat. As the tone deviated from this position, perceptual judgments were degraded:
Figure 19
Fig. 19. Effect of temporal position on accuracy of pitch judgment. (See also Fig. 18.) Jones, Moynihan, MacKenzie &
Puente (in press) showed that pitch judgments are most accurate when the tone judged occurs in an expected temporal position (position 3).
This research reinforces and extends the general principles we have already seen operating with regard to auditory expectation. Specifically,
Expectations facilitate perception.
It is not simply the case that expectations prepare an organism to take appropriate action. In the case of temporal expectations, we see that listeners expect to receive information at certain times. The
listener may not know what is going to happen, but might
nevertheless anticipate the moment when the information arrives. One can imagine a number of ways in which accurate expectations facilitate perception. The prospect of perceiving something with greater accuracy could well be responsible for encouraging an
organism to attempt to form accurate expectations about the future. In this sense, temporal expectations are akin to the orienting
response -- a behavior that improves perception.
In addition, expectations can be viewed as preparations for appropriate motor behaviors.
1.
Expectations are shaped by context.
As in the case of pitch perception, rhythmic expectations are related to the context. Some contexts are quite general, as when we
experience music in simple-duple meter, or compound-triple meter. At the other extreme, we may expect a particular temporal organization because of extensive familiarity with a particular rhythm or musical work. That is, rhythmic expectations may arise through veridical contexts.
It is also possible that listeners form schematic expectations that are culture- or genre-related. Consider, for example, the siciliano -- a leisurely baroque dance form. The siciliano is generally in 6/8 meter, although occasionally it is found in 12/8. In addition to this
compound-duple metric framework, there are stereotypic rhythms the occur in this form and that contribute to the stylistic cliché for the
siciliano. The most distinctive feature is the dotted-eighth/sixteenth
figure that begins the measure, and the quarter-note in the mid-measure position, followed by either an eighth-note or two sixteenths:
Figure 20
Fig. 20. Two rhythmic patterns commonly found in siciliano dance forms.
Schubert's famous Christmas carol, Stille Nacht ("Silent Night"), exhibits the distinctive sciliano rhythm. Below is a cumulative onset histogram for a sample of bars from various siciliana, showing the relative frequency of occurrence for various points in the 6/8 metric hierarchy.
Figure 21
Fig. 21. Cumulative onset histogram for a sample of bars from various siciliana movements, showing the relative frequency of occurrence for various points in the 6/8 metric hierarchy.
Once established, listeners readily expect the rhythm. In this case we can see that it is not simply the strict hierarchical metrical frameworks that influence a listener's temporal expectations. In addition to these
metric expectations, listeners can also form distinctly rhythmic
expectations which can employ non-regular duration patterns.
Expectations can be tailored for different rhythms: sambas, tangos, rock back-beats, and so on. Similarly, complex African rhythms can evoke specific temporal expectations for those listeners who are familiar with them. [3]
Temporal expectations are learned.
Although no one has provided a formal demonstration, it is quite likely that rhythmic expectations are shaped by the same statistical learning of the auditory environment that we've seen for pitch. The reason why periodic pulse and meter are common in music is that these patterns are the easiest patterns for which brains are able to form expectations. In this regard, the metric hierarchy is truly analogous to a scale or scale hierarchy. Metric positions provide convenient "bins" for expected stimuli.
While periodicity is helpful for listeners, periodicity is not necessary in order to form temporal expectations. It is important only that the listener be experienced with the temporal structure, and that some element of the temporal pattern be predictable. An illustration of this point can be found in the expectation for "bouncing" rhythms (see Fig. 22). Although the sound of something bouncing is not periodic, the inter-bounce interval shortens predictably as the bouncing continues and so listeners are able to predict, to some degree, the temporal sequence of events. In music, this accelerating rhythm can be found in Tibetan monastic music (where it is frequently played on cymbals). In Western music, there is no known instance of this accelerating rhythm prior to the twentieth century.
Figure 22
Fig. 22. Schematic representation of accelerating onsets characteristic of the sound produced by a bouncing object. Although the pattern is not metrically regular, it is
nevertheless predictable. 3.