Effects of syllable-final segment duration on the identification of synthetic speech continua by birds and humans

In an attempt to test whether experience with or knowledge of language is necessary to show typical speaking rate effects in the perception of speech, budgerigars (Melopsittacus undulatus) and humans categorized stimuli from the synthetic continua /ba/-/wa/ and /bas/-/was/, with both short and long syllable-final phonemes. This comparative approach aims to shed some light on whether knowledge of language has a role in rate normalization effects, such as using duration information as an indicator of speaking rate in human speech perception. Syllable-final phoneme durations were varied, and were either temporally adjacent to the initial target (CV series) or were nonadjacent (CVC series). The birds were always influenced by syllable-final duration variation in the present experiments and displayed greater boundary shifts than humans. In humans, there was a significant boundary shift observed in the CV series, but there were no effects of duration variation in the final segment in the CVC series. The results from the birds suggest that specialized speech-based principles may not be necessary for explaining findings of grouping speech or speechlike elements in perception.