No abstract

European starlings (Sturnus vulgaris) were trained to discriminate two complex harmonic structures modeled after musical chords in a 2-alternative choice task. Musical chords provide rich acoustic structures with which to study relative pitch perception and perceptual invariance in nonhuman animals. The starlings learned the chord discrimination and transferred the discrimination to chords with different root frequencies, thus showing perceptual invariance for the chords. Further transfer tests showed that correlates of chord structure were indeed controlling discrimination performance. The proposition that the starlings were responding primarily to a sensory dimension of consonance and dissonance in the acoustic structures provides a good account of the data. The harmonic principles that govern consonance and dissonance may be important for starling auditory communication and, perhaps, auditory communication of other songbirds. From the standpoint of human music cognition, the data add to previous observations suggesting that the idea of musical universals may be extended to species other than humans.In this article, we extend a comparative study of the perception of complex acoustic structures by songbirds to the pitch structures defined by musical chords. We doubt that the chords of Western music as such have any direct significance to starlings (Sturnus vulgaris). However, the structure of musical chords leads to some perceptual properties (for humans, at any rate) that may have significance for avian communication, and for that reason chords provide an interesting tool with which to examine perceptual processes that may, in fact, play an important role in nature. For example, chords are rich in pitch relations among their component tones. Pitch relations have been shown to be relevant for communication in at least some species of songbird, for example, black-capped chickadees (Parus atricapillus; Weary & Weisman, 1991) and white-throated sparrows (Zonotrichia albicollis; Hurly, Ratcliffe, & Weisman, 1990). Furthermore, constant relations among the spectral properties of natural sounds have been shown to be potentially relevant for communication in zebra finches (Taeniopygia guttata;Cynx, Williams, & Nottebohm, 1990) and starlings (Braaten & Hulse, 1991).

The sensitive period is a special time for auditory learning in songbirds. However, little is known about perception and discrimination of song during this period of development. The authors used a go/no-go operant task to compare discrimination of conspecific song from reversed song in juvenile and adult zebra finches (Taeniopygia guttata), and to test for possible developmental changes in perception of syllable structure and syllable syntax. In Experiment 1, there were no age or sex differences in the ability to learn the discrimination, and the birds discriminated the forward from reversed song primarily on the basis of local syllable structure. Similar results were found in Experiment 2 with juvenile birds reared in isolation from song. Experiment 3 found that juvenile zebra finches could discriminate songs on the basis of syllable order alone, although this discrimination was more difficult than one based on syllable structure. The results reveal well-developed song discrimination and song perception in juvenile zebra finches, even in birds with little experience with song.

Four European starlings (Sturnus vulgaris) discriminated a 300-ms segment of starling song from a 300-ms segment of budgerigar song in three contexts in a two-choice key-peck operant discrimination task. In the starling-song context, on each trial, one of the song segments was presented in the context of starling song; in the budgerigar-song context, the segments were presented in the context of budgerigar song. In the no-song context, the song segments were presented outside of a song context. On occasional unreinforced probe trials, the song segments were replaced by either white noise or silence. On noise trials in the two song contexts, but not on silent trials in the song contexts or noise trials in the no-song context, the starlings were significantly more likely to respond to the key associated with the starling song segment than to the key associated with the budgerigar song segment. This effect was especially pronounced in the starling-song context. The results indicate that noise induces perceptual restoration of missing birdsong segments in songbirds.

If one stimulus pattern is transposed to another, and if the two are recognizably the same, then they are said to be perceptually invariant. Usually, transpositions that lead to perceptual invariance involve changes on a ratio scale between the stimuli comprising the two patterns. In this paper, we survey the literature with a view to the conditions of pitch structure (melody and harmony), spectral structure (timbre), intensity structure (loudness), and temporal structure (rhythm, meter, and tempo) that produce perceptual invariance. The review compares perceptual invariance for human infants, young children, and adults and nonhuman animals. For the most part, perceptual invariance holds at all levels of development and for all species throughout the acoustic dimensions surveyed. However, for melody perception, there is evidence that humans go through a stage in early childhood in which absolute (as distinguished from relative) pitch perception plays a role. Without doubt, absolute pitch is important in perception of serial acoustic (melodic) structures by animals. For both humans and nonhumans, melody perception appears to be governed by a hierarchy of perceptual strategies that includes both absolute and relative pitch. The survey suggests the value of a comparative perspective in understanding the perceptual principles underlying music perception in humans and the principles by which human infants and nonhuman animals process acoustic information.