ABSTRACT
At first glance, Figure 23.1 shows what appears to be a black candleholder, or vase, on a white background. However, if the viewer focuses attention on the contour boundary between the white and black regions, two white faces staring at each other over a black background may be perceived instead. is visual perception phenomenon is known as gure-ground reversal. As we gaze at visual stimuli such as these, the gure (or foreground) and the ground (or background) spontaneously switch their roles. is perceptual phenomenon has been exploited in the work of several artists, including Salvador Dali, who used it quite successfully in several paintings such as the Slave Market with Disappearing Bust of Voltaire.*
A similar phenomenon occurs in the domain of aural perception of rhythms. Consider the two rhythms shown in Figure 23.2. Let the rhythm on the le be the lead rhythm (gure) played on a high-pitched conga, and the one on the right be the accompaniment (background) played on a low-pitched conga. If both rhythms are played at the same volume, then the listener’s attention may shi back and forth spontaneously, or at will, to perceive either the rhythm on the le or the one on the right.*
Note that in Figure 23.2, the rhythm on the right consists of onsets at the positions of the silent pulses contained in the rhythm on the le , and vice versa. Such rhythms are called complementary.† Together, they ll the entire set of pulse locations in the cycle, and are thus also referred to as interlocking‡ rhythms. Interlocking rhythms constitute one of the main principles of rhythm integration in African drumming.§ In this particular case, both rhythms belong to the same necklace: one rhythm is a rotation of the other. us, this aural example is not completely analogous to the visual example in Figure 23.1, where the gure (candle holder) and the ground (two faces) are completely dierent patterns. However, analogous examples with two dierent complementary rhythms are also possible, as Figure 23.3 illustrates. e rhythm on the le is the illustrious bembé rhythm (also diatonic scale in the pitch domain), and the one on the right is a rotation of the equally prominent fumefume rhythm (also pentatonic scale in the pitch domain). e “audible” beats of one rhythm are the “empty” beats of the other.¶ It is interesting that both the seven-onset bembé timeline and its complement are both highly prominent in sub-Saharan African traditional
music. Playing both together on dierent drums at the same volume also produces in the listener spontaneous gure-ground reversals between the two timelines.
