Perceptual Coherence : Hearing and Seeing

(A)
(B)
Warbleness
The Transition Between Noise and Structure 185
Figure 4.14. The tonal strength (A) and degree of warble (B) for repeating random
noise segments.
shorter-duration segments, the reverse was true. Listeners were more likely
to maintain the combined AB segment as the repeating unit, so that the timbre
did not vary (e.g., the sequence AAAABBBBAAAABBBB was perceived
as the repetition of [AAAABBBB]). For example, for 2 ms segments
(500 Hz), the strong perception of alternating timbres for ABAB sequences
occurred only for 12 or more repetitions (e.g., in shorthand notation 12A,
12B, 12A, 12B) but the perception of timbre changes for ABCD sequences
occurred for 4 or more repetitions (e.g., 4A, 4B, 4C, 4D). There was a perceptual
tendency to hang onto the perception of one repeating segment until
it produced such long-duration segments that the perception of a strong
pitch became problematic. At that point, the perception of warble began, and
its strength grew as the number of repetitions increased further. A more extreme
example occurred for the .5 ms segments (2000 Hz). If the segments
alternated, it took more than 48 repetitions (48A, 48B, 48A, 48B) before the
perception of warble occurred. Thus, it appears that the fundamental factor
in determining the tonal perception for ABAB sequences is the number