Rhythmic Entrainment in Kea Parrots (Nestor Notabilis)

Abstract

Rhythmic entrainment or beat perception and synchronization (BPS) occurs when a subject synchronizes their movements with a rhythmic stimulus based on extracting periodicities from the rhythmic stimulus, and temporal anticipation (predicting the next pulse) [1]. Researching that phenomenon in non-human animals can help settle the dilemma of the evolutionary origins of rhythmicality and musicality. By testing the ability of kea parrots (Nestor notabilis) to spontaneously entrain to a regular beat, we also aim to support or reject the “vocal learning and rhythmic synchronization hypothesis” [2], which predicts that only vocal learning species are capable of rhythmic entrainment, as is supported by studies of different vocal learning species, most notably of the parrot (Psittaciformes) order. Simply put, vocal learning is the ability to produce sounds that are not part of an innate repertoire (e. g. by imitation).

The theory is based on the fact, that both BPS and vocal learning involve links between auditory and motor systems [3]. Compared to other parrots, Kea have reduced vocal learning abilities. So far, few vocal non-learning species have been tested for PBS, and often on a very limited subject sample. Kea are closely related to vocal learning species (parrots) but such behavior has not yet been noted with them, which makes it hard to classify them as vocal learners or reject them as vocal non-learners. They do, however, display synchronization in some of their social behaviors.

In our ongoing research, we are testing whether kea spontaneously entrain to an isochronous beat while performing a repetitive motor task. Nine kea have already been trained to solve a sequential task consisting of eight equidistant dots, displayed in two rows on a touchscreen display, which have to be tapped in a set order. In the following weeks, a metronome sound will be introduced while the kea will be solving the sequential task. In that way, three conditions will be tested. In the “baseline” condition, the metronome beat will match the inter-tap interval (ITI) of each individual. If the kea reduce the variability in their ITIs, this will be considered entrainment. For the “fast” and “slow” conditions, the metronome beat will be sped up or slowed down by 15% of the baseline, respectively. If the subjects match their ITI to those speeds, that will be considered entrainment.

If the kea entrain to the metronome, it could be claimed that BPS has not necessarily evolved solely from neural circuits responsible for complex vocal learning, but rather that it evolved from other behaviors that require synchronization (such as chorusing), or that the origin of all these behaviors lies elsewhere.

References

[1] Hasegawa, A., Okanoya, K., Hasegawa, T., & Seki, Y. (2011c). ‘Rhythmic synchronization tapping to an audio-visual metronome in budgerigars’, Scientific Reports, 1(1).doi:10.1038/srep00120.

[2] Patel, A.D. (2006) ‘Musical Rhythm, linguistic rhythm, and human evolution’, Music Perception, 24(1), pp. 99–104. doi:10.1525/mp.2006.24.1.99.

[3] Schachner, A. et al.(2009) ‘Spontaneous motor entrainment to music in multiple vocal mimicking species’, Current Biology, 19(10), pp. 831–836. doi:10.1016/j.cub.2009.03.061.