Friday, May 20, 2016

Can birds perceive rhythmic patterns?

The specific question whether animals can detect regularity in a stimulus and synchronize their own behavior to arbitrary rhythmic patterns got sudden attention with the discovery of Snowball, a sulphur-crested cockatoo that could synchronize head and body movements with the beat in several popular songs (see earlier entry). Parrots, such as Snowball, are vocal learners and vocal learning is associated with evolutionary modifications to the basal ganglia, which play a key role in mediating a link between auditory input and motor output during learning. As such linkage between auditory and motor areas in the brain is also required for beat induction, Patel suggested that only vocal learning species might be able to show beat induction. However, further studies have shown the picture to be more complicated (see earlier entry) and this calls for a re-examination of the link between vocal learning and beat perception and induction. While zebra finches (vocal learners) are able to discriminate a regular isochronous from an irregular stimulus (Van der Aa et al., 2015), this discrimination was strongly reduced with tempo transformations (changing rate, but not the regularity of the stimulus). Zebra finches seem to attend strongly to specific local features of the individual stimuli (e.g. the exact duration of time intervals) rather than the overall regularity of the stimuli, which was the main feature human listeners attended to (Van der Aa et al., 2015).

Figure 3 from Ten Cate et al. (2016)
In a recent paper (Ten Cate et al., 2016) we review the available experimental evidence for the perception of regularity and rhythms by birds, like the ability to distinguish regular from irregular stimuli over tempo transformations and report data from new experiments. While some species show a limited ability to detect regularity, most evidence suggests that birds attend primarily to absolute and not relative timing of patterns and to local features of stimuli. We conclude that, apart from some large parrot species, there is limited evidence for beat and regularity perception among birds and that the link to vocal learning is unclear. We next report experiments in which zebra finches and budgerigars (both vocal learners) were first trained to distinguish a regular from an irregular pattern of beats and then tested on various tempo transformations of these stimuli. The results showed that both species reduced the discrimination after tempo transformations. This suggests that, as was found in earlier studies, they attended mainly to local temporal features of the stimuli, and not to their overall regularity. However, some individuals of both species showed an additional sensitivity to the more global pattern if some local features were left unchanged. Altogether our study indicates both between and within species variation, in which birds attend to a mixture of local and global rhythmic features. van der Aa, J., Honing, H., & ten Cate, C. (2015). The perception of regularity in an isochronous stimulus in zebra finches (Taeniopygia guttata) and humans Behavioural Processes, 115, 37-45 DOI: 10.1016/j.beproc.2015.02.018 ten Cate, C., Spierings, M., Hubert, J., & Honing, H. (2016). Can Birds Perceive Rhythmic Patterns? A Review and Experiments on a Songbird and a Parrot Species Frontiers in Psychology, 7 DOI: 10.3389/fpsyg.2016.00730

Sunday, May 08, 2016

Can humans listen like songbirds do?

European Starling ©

Humans and songbirds share many interesting similarities with regard to their auditory processing capabilities. For example, we know that humans and European Starlings have similar frequency sensitivity, perceive the pitch of the missing fundamental, and parse multiple pure-tone sequences into separate auditory streams. At higher levels, the “musical” nature of birdsong has long been appreciated by humans, and some songbirds can readily learn to discriminate and imitate human melodic sequences (cf. Hoeschele et al., 2015).

Given these similarities, it is surprising to find a major difference in how humans and songbirds perceive sequences of tones. Humans readily recognize tone sequences that are shifted up or down in log frequency because the pattern of relative pitches is maintained (referred to as relative pitch). In contrast, songbirds appear to have a strong bias to rely on absolute pitch for the recognition of tone sequences (a pitch-shifted melody might well be perceived as an altogether different melody; Hoeschele et al., 2015).

Interestingly, a recent study by Bregman et al. (2016), contrasting pitch and spectral patterns, shows that birds perceive their song more like humans perceive speech (Shannon, 2016). More precisely, songbirds might attend more to the acoustic spectral shape than to the absolute pitch of the acoustic signal. Stimuli that preserve acoustic spectral shape, even in the absence of pitch, seem to allow for generalization of learned acoustic patterns. Hence it could well be that a sensitivity to spectral shape is what is shared between human and avian cognition of musical signals, while relative pitch is the preferred mode of listening for humans. And one could wonder: why is sound "super normally stimulated" in humans (see earlier entry), and can humans be made to change their listening mode in the direction of birds (or vice versa) when manipulating melody and spectral shape? Bregman, M., Patel, A., & Gentner, T. (2016). Songbirds use spectral shape, not pitch, for sound pattern recognition Proceedings of the National Academy of Sciences, 113 (6), 1666-1671 DOI: 10.1073/pnas.1515380113 Hoeschele, M., Merchant, H., Kikuchi, Y., Hattori, Y., & ten Cate, C. (2015). Searching for the origins of musicality across species Philosophical Transactions of the Royal Society B: Biological Sciences, 370 (1664), 20140094-20140094 DOI: 10.1098/rstb.2014.0094 Shannon, R. V. (2016). Is Birdsong More Like Speech or Music? Trends in Cognitive Sciences, 20 (4), 245-247 DOI: 10.1016/j.tics.2016.02.004