Music perception and octave generalization in rhesus monkeys

Area of Science:

• Animal Behavior
• Music Perception
• Comparative Cognition

Background:

• Octave generalization, the ability to recognize a melody regardless of its pitch level, is a fundamental aspect of human music perception.
• Understanding the cognitive mechanisms underlying music perception in non-human primates can provide insights into the evolutionary origins of music.

Purpose of the Study:

• To investigate whether rhesus monkeys exhibit octave generalization for musical stimuli.
• To determine if monkeys process tonal melodies as coherent gestalts that maintain identity across octave transpositions.

Main Methods:

• Two rhesus monkeys were trained to discriminate between same and different musical passages.
• Passages included familiar songs, tonal melodies, atonal melodies, and random-synthetic sequences, transposed by various octave intervals.
• Judgments of same/different were recorded for each stimulus type and transposition.

Main Results:

• Monkeys showed complete octave generalization for familiar childhood songs and algorithmically generated tonal melodies.
• No octave generalization was observed for random-synthetic melodies, atonal melodies, or individual notes.
• Generalization was robust for whole-octave (1 and 2 octave) transpositions but diminished for fractional (0.5 and 1.5 octave) transpositions of familiar songs.

Conclusions:

• Tonal melodies are perceived as musical gestalts by rhesus monkeys, similar to humans.
• Monkeys preserve the identity of tonal melodies when transposed by whole octaves, indicating chroma constancy.
• These findings suggest shared neural mechanisms for music processing and memory in primates, with implications for the nature vs. nurture debate in music perception.