BIRDSONG AND HUMAN SPEECH: Common Themes and Mechanisms

Abstract

Human speech and birdsong have numerous parallels. Both humans and songbirds learn their complex vocalizations early in life, exhibiting a strong dependence on hearing the adults they will imitate, as well as themselves as they practice, and a waning of this dependence as they mature. Innate predispositions for perceiving and learning the correct sounds exist in both groups, although more evidence of innate descriptions of species-specific signals exists in songbirds, where numerous species of vocal learners have been compared. Humans also share with songbirds an early phase of learning that is primarily perceptual, which then serves to guide later vocal production. Both humans and songbirds have evolved a complex hierarchy of specialized forebrain areas in which motor and auditory centers interact closely, and which control the lower vocal motor areas also found in nonlearners. In both these vocal learners, however, how auditory feedback of self is processed in these brain areas is surprisingly unclear. Finally, humans and songbirds have similar critical periods for vocal learning, with a much greater ability to learn early in life. In both groups, the capacity for late vocal learning may be decreased by the act of learning itself, as well as by biological factors such as the hormones of puberty. Although some features of birdsong and speech are clearly not analogous, such as the capacity of language for meaning, abstraction, and flexible associations, there are striking similarities in how sensory experience is internalized and used to shape vocal outputs, and how learning is enhanced during a critical period of development. Similar neural mechanisms may therefore be involved.

The biology and evolution of music: A comparative perspective

“…Vocal play as a precursor of adult birdsong is of course perfectly intelligible in these terms, and the ubiquity of subsong in birds suggests that it is not only useful, but perhaps necessary, if an individual is to reliably master a complex vocal repertoire. Similar comments can be made about babbling and language acquisition (Doupe & Kuhl, 1999).…”

“…At the behavioural level, song-learning birds go through a ''sensitive period'' early in life, when they must be exposed to normal conspecific song if they are to develop normal singing behaviour (Marler, 1987), paralleling the critical or sensitive periods documented for some aspects of language and music learning in humans (Newport, 1991;Trainor, 2005). Perhaps related, birds with vocal learning go through an immature stage where they produce highly variable song, termed ''subsong'', which develops towards an accurate rendition of their tutorsÕ song during a process of successive experimentation and approximation (Doupe & Kuhl, 1999;Tchernichovski, Mitra, Lints, & Nottebohm, 2001). This process, which creates a self-stimulatory auditory/motor loop, has been shown in a few species to be necessary for adequate song learning (cf.…”

“…The classic example, birdsong, is based on an ability to learn vocalizations that has evolved at least three times in birds (songbirds, parrots and hummingbirds (Doupe & Kuhl, 1999)). I will focus here on songbirds, which are by far the best-understood of these groups.…”

“…Doupe & Kuhl, 1999;Fitch, 2000;Marler, 1976;Nottebohm, 1976). Perhaps surprisingly, the parallels with language have received far more attention (Marler, 2000).…”

Brain and cognitive evolution: Forms of modularity and functions of mind.

“…Invariant patterns are those that provide reliable and consistent information about conditions that have covaried with survival or reproductive outcomes during the species' evolutionary history. Examples include motion patterns generated by conspecifics (e.g., Blake, 1993;Grossman et al, 2000), shape and coloration of fruit for fruit-eating species (Barton et al, 1995), and acoustical patterns generated by human vocalizations (Doupe & Kuhl, 1999), among many others. We predict that an evolved sensitivity to variant information patterns occurs when discriminations within broader, invariant categories result in survival or reproductive advantages.…”