Scale, key, and contour in the discrimination of tuned and mistuned approximations to melody.

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Approximations to melody were synthesized using a computational technique whereby the occurrences of certain notes and intervals were made more probable than others. In experimental melodies, these notes and intervals were chosen to clarify the diatonic scale and the key of the melody. To clarify the scale of a melody, the probabilities of the diatonic scale notes were made higher than those of nonscale notes. Perception of these melodies was compared with control melodies in which the higher probabilities were assigned to a different set of notes. The latter were chosen so that no single diatonic scale embraced the set. To clarify the key of a melody, intervals with a low “fifth-span” were made more probable than intervals with a high fifth-span, while control melodies had the higher probabilities assigned to intervals with a high fifth-span. Here fifth-span is the separation of two notes measured along a progression of fifths. Listeners heard pairs of melodies and were asked to discriminate between pairs of different melodies and pairs in which the second melody was an exact transposition of the first. It was found that this discrimination was easier if the first melody contained a high proportion of diatonic-scale notes. A similar perceptual advantage held for melodies composed of intervals with low fifth-spans. Discrimination was also easier if the contour of the second melody in a different-pair differed from that of the first. The melodies were then mistuned by changing the size of the quantal interval (semitone) by a constant (log) factor. In this way, two types of mistuned melodies were generated: melodies for which the quantal interval was reduced, and melodies for which the quantal interval was increased. Discrimination advantages for diatonic scale and low fifth-span were not found for these mistuned melodies. Nevertheless, differences in contour still led to improved discrimination. It is concluded that melody perception draws on music-specific perceptual knowledge as well as more general factors. Mistuning destroys the perceptual advantages found for the melodies with a clear scale and a clear key. These attributes are therefore considered to be specific to music. By contrast, the perceptual salience of pitch contours is more general in origin, because it was shown for both the tuned and the mistuned tone sequences.