Macaque monkeys discriminate pitch relationships. Brosch, M., Selezneva, E., Bucks, C., & Scheich, H. Cognition, 91(3):259-272, 2004.
abstract   bibtex   
This study demonstrates that non-human primates can categorize the direction of the pitch change of tones in a sequence. Two Macaca fascicularis were trained in a positive-reinforcement behavioral paradigm in which they listened to sequences of a variable number of different acoustic items. The training of discriminating pitch direction was divided into three phases with increasing task complexity. In the first two phases, subjects learned to employ a same/different rule. In phase I, they discriminated acoustic items of different sound quality. Subjects had to respond when there was a change from repeating noise bursts to repeating click trains or vice versa. In phase II, acoustic items differed along one physical dimension only. Subjects had to respond to a change of the frequency of a repeating series of pure tones. In phase III, sequences consisted of three series of repeating tones of different frequency. Subjects were required to respond when the frequency of the tones changed in a downward direction and to refrain from responding when the frequency remained constant or increased. After several ten thousand trials, subjects categorized pitch direction well above chance level. The discrimination was performed over a 4.5-octave range of frequencies and was largely independent of the temporal and ordinal position of the downward pitch direction within the sequence. These results demonstrate that monkeys can recognize pitch relationships and thus that monkeys have the concept of ordinal relations between acoustic items.
@ARTICLE{Brosch2004,
  author = {Michael Brosch and Elena Selezneva and Cornelia Bucks and Henning
	Scheich},
  title = {Macaque monkeys discriminate pitch relationships},
  journal = {Cognition},
  year = {2004},
  volume = {91},
  pages = {259-272},
  number = {3},
  abstract = {This study demonstrates that non-human primates can categorize the
	direction of the pitch change of tones in a sequence. Two Macaca
	fascicularis were trained in a positive-reinforcement behavioral
	paradigm in which they listened to sequences of a variable number
	of different acoustic items. The training of discriminating pitch
	direction was divided into three phases with increasing task complexity.
	In the first two phases, subjects learned to employ a same/different
	rule. In phase I, they discriminated acoustic items of different
	sound quality. Subjects had to respond when there was a change from
	repeating noise bursts to repeating click trains or vice versa. In
	phase II, acoustic items differed along one physical dimension only.
	Subjects had to respond to a change of the frequency of a repeating
	series of pure tones. In phase III, sequences consisted of three
	series of repeating tones of different frequency. Subjects were required
	to respond when the frequency of the tones changed in a downward
	direction and to refrain from responding when the frequency remained
	constant or increased. After several ten thousand trials, subjects
	categorized pitch direction well above chance level. The discrimination
	was performed over a 4.5-octave range of frequencies and was largely
	independent of the temporal and ordinal position of the downward
	pitch direction within the sequence. These results demonstrate that
	monkeys can recognize pitch relationships and thus that monkeys have
	the concept of ordinal relations between acoustic items.}
}

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