Academic journal article Perception and Psychophysics

An Interval Size Illusion: The Influence of Timbre on the Perceived Size of Melodic Intervals

Academic journal article Perception and Psychophysics

An Interval Size Illusion: The Influence of Timbre on the Perceived Size of Melodic Intervals

Article excerpt

In four experiments, we investigated the influence of timbre on perceived interval size. In Experiment 1, musically untrained participants heard two successive tones and rated the pitch distance between them. Tones were separated by six or seven semitones and varied in timbre. Pitch changes were accompanied by a congruent timbre change (e.g., ascending interval involving a shift from a dull to a bright timbre), an incongruent timbre change (e.g., ascending interval involving a shift from a bright to a dull timbre), or no timbre change. Ratings of interval size were strongly influenced by timbre. The six-semitone interval with a congruent timbre change was perceived to be larger than the seven-semitone interval with an incongruent timbre change (interval illusion). Experiment 2 revealed similar effects for musically trained participants. In Experiment 3, participants compared the size of two intervals presented one after the other. Effects of timbre were again observed, including evidence of an interval illusion. Experiment 4 confirmed that timbre manipulations did not distort the perceived pitch of tones. Changes in timbre can expand or contract the perceived size of intervals without distorting individual pitches. We discuss processes underlying interval size perception and their relation to pitch perception mechanisms.

One of the most basic findings in music cognition is that listeners are highly sensitive to relative pitch. Relative pitch refers to relations between pitches-for example, whether one pitch is higher or lower than another, or whether two pitches are proximate (forming a small pitch interval) or far apart (forming a large pitch interval). From about the age of 6, relative pitch processing is evident for most listeners (Takeuchi & Hulse, 1993). Relative pitch is exemplified by the psychological similarity between two pitch intervals that have the same fundamental frequency ratio but differ in absolute pitch values. For example, the pitch interval formed by tones with fundamental frequencies of 200 and 300 Hz (the pitch distance between the first and second twinkles in "Twinkle, Twinkle Little Star") is psychologically similar to the pitch interval formed by tones with fundamental frequencies of 400 and 600 Hz, and both intervals are defined by the same musical label (perfect fifth).

Musically trained listeners possess explicit knowledge of interval categories that is manifested in the ability to assign labels to intervals (e.g., perfect fifth or octave). Untrained listeners possess implicit knowledge of interval categories (Smith, Nelson, Grohskopf, & Appleton, 1994). Such knowledge is evident when a familiar melody (e.g., "Happy Birthday") is recognized even though it is sung at a novel pitch level. Untrained listeners can also tell whether a melody is sung poorly or out of tune.

Factors other than fundamental frequency affect relative pitch. For example, intervals with similar harmonic functions in Western music, such as a perfect fifth (seven semitones) and a perfect fourth (five semitones) have greater psychological similarity than intervals with different harmonic functions (Krumhansl, 1979; Schellenberg & Trainor, 1996). Expectations can also affect relative pitch. The same interval will be perceived as slightly larger or smaller depending on whether it is larger or smaller than expected (Russo & Thompson, in press; Shepard & Jordan, 1984) and whether it is moving toward or away from the center of an established pitch range (Russo & Thompson, in press). Moreover, when embedded in a melody, the same interval will create a stronger or weaker melodic accent depending on the rhythmic context (e.g., Boltz & Jones, 1986; Jones, Moynihan, MacKenzie, & Puente, 2002).

The effects of timbre on the perception of pitch are complex. Certain manipulations to the frequency and phase spectrum of a tone can result in changes to the perceived pitch of that tone (e. …

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