Social, Ecological and Genetic Variables in a Model Learning System
Michael D. Beecher
The use of elaborate acoustic vocalizations for communication is common in a wide variety of animal groups. In the oscine passerines (songbirds), such vocalizations are called song and have an additional, intriguing aspect: they are learned, with much of that learning occurring very early in life. Song learning in songbirds has been extensively analyzed in the laboratory and has become a major model system for studying the neurobiology of learning. Its value as a model system is enhanced by its many parallels with human language learning. These parallels include an early sensitive period, a perceptual filtering mechanism tuned to species communication signals, a crucial role for auditory feedback in normal development, a separation between sensory and motor learning, and an early subsong or babbling stage. Work on the neural basis of song perception and production in songbirds has revealed additional parallels between the neural centers for song in birds and those for language in humans. In this context, understanding the normal course of song development in songbirds becomes crucial if this model system is going to provide general insights into the development of vocal communication systems in general and human language in particular. Unfortunately, our understanding of normal song development is surprisingly incomplete, because most studies of song learning to date have been laboratory experiments in which essentially all social features have been removed. Four series of studies will be carried out to examine social, ecological and genetic variables in the song learning process for one particular species, the song sparrow. In the first series of experiments, singing interactions between tutor and tutee, and between tutors, will be manipulated and analyzed as a potential variable in song learning; this will be the first time this has been attempted in the laboratory. The setup will simulate four live song tutors, and both tutor-tutor and tutor-tutee singing interactions will be systematically varied; the general prediction is that birds will copy more songs from more interactive tutors. A second study will examine the role of genetic factors by comparing song learning by eastern and western song sparrows. On the basis of field studies, it has been hypothesized that birds in the two populations follow very different, genetically-based song-learning programs. This hypothesis will be tested by collecting birds from both populations and raising them in a common song-tutoring regime; according to the genetic hypothesis, the differences observed in the field should persist despite the common tutoring regime. In a third study, song learning will be directly examined in the field by radio-tracking young song sparrows through their first year and correlating the extent and timing of their interactions with potential song tutors and the degree to which the young birds copy their songs. In the fourth study, playback experiments in which the experimenter simulates a birds neighbor by playing recordings of the neighbor to the bird in a realistic simulation -- will be carried out to analyze how birds in both populations use their songs in territorial interactions with their neighbors. Field studies have suggested that the rules of communication in these two populations may be quite different, paralleling the presumed difference in their song learning programs. It is hoped that results from these different lines of research will combine to elucidate the social factors that shape the development of this model vocal learning system. In turn, such insights may shed light on human disorders such as autism that are characterized by a co-occurrence of language and social deficiencies.
