Revisiting vocal perception in non-human animals: a review of vowel discrimination, speaker voice recognition, and speaker normalization

The extent to which human speech perception evolved by taking advantage of predispositions and pre-existing features of vertebrate auditory and cognitive systems remains a central question in the evolution of speech. This paper reviews asymmetries in vowel perception, speaker voice recognition, and speaker normalization in non-human animals - topics that have not been thoroughly discussed in relation to the abilities of non-human animals, but are nonetheless important aspects of vocal perception. Throughout this paper we demonstrate that addressing these issues in non-human animals is relevant and worthwhile because many non-human animals must deal with similar issues in their natural environment. That is, they must also discriminate between similar-sounding vocalizations, determine signaler identity from vocalizations, and resolve signaler-dependent variation in vocalizations from conspecifics. Overall, we find that, although plausible, the current evidence is insufficiently strong to conclude that directional asymmetries in vowel perception are specific to humans, or that non-human animals can use voice characteristics to recognize human individuals. However, we do find some indication that non-human animals can normalize speaker differences. Accordingly, we identify avenues for future research that would greatly improve and advance our understanding of these topics.

High Level of Song Sharing in an Eastern Population of Song Sparrow (Melospiza Melodia)

Using shared songs is believed to be an integral part of neighbor communication and territory establishment strategies among many avian species with repertoires. Previous studies of two western subspecies of Song Sparrows (Melospiza melodia) reported a high level of song sharing among neighboring males, whereas studies of an eastern subspecies have reported a very low level. The purpose of our study was to investigate another population of the eastern subspecies to determine whether higher song-sharing levels existed within its range. Every song in the repertoire of 29 males was compared with the songs of all other males to assess the number of shared songs. For each male, we calculated the mean song-sharing level with neighbors and non-neighbors. Males shared, on average, 33% of their repertoire with neighbors, significantly more than they shared with non-neighbors (27% of their repertoire). Two first-year males learned whole song types from several individuals and preferentially learned the song types shared among those individuals. Our results suggest that the eastern and western subspecies may not differ genetically in the way they learn songs, because song-sharing levels and song learning in our population were more similar to those of the western subspecies than to those of other populations within its own subspecies. Song-sharing differences among eastern populations may be explained instead by factors acting at the level of individual populations.

Niveau Élevé de Chants Partagés chez une Population de l'Est de Melospiza melodia