Article

Birds, primates, and spoken language origins: Behavioral phenotypes and neurobiological substrates

Institute of Neuroscience, Newcastle University Newcastle upon Tyne, UK.
Frontiers in Evolutionary Neuroscience 08/2012; 4:12. DOI: 10.3389/fnevo.2012.00012
Source: PubMed

ABSTRACT

Vocal learners such as humans and songbirds can learn to produce elaborate patterns of structurally organized vocalizations, whereas many other vertebrates such as non-human primates and most other bird groups either cannot or do so to a very limited degree. To explain the similarities among humans and vocal-learning birds and the differences with other species, various theories have been proposed. One set of theories are motor theories, which underscore the role of the motor system as an evolutionary substrate for vocal production learning. For instance, the motor theory of speech and song perception proposes enhanced auditory perceptual learning of speech in humans and song in birds, which suggests a considerable level of neurobiological specialization. Another, a motor theory of vocal learning origin, proposes that the brain pathways that control the learning and production of song and speech were derived from adjacent motor brain pathways. Another set of theories are cognitive theories, which address the interface between cognition and the auditory-vocal domains to support language learning in humans. Here we critically review the behavioral and neurobiological evidence for parallels and differences between the so-called vocal learners and vocal non-learners in the context of motor and cognitive theories. In doing so, we note that behaviorally vocal-production learning abilities are more distributed than categorical, as are the auditory-learning abilities of animals. We propose testable hypotheses on the extent of the specializations and cross-species correspondences suggested by motor and cognitive theories. We believe that determining how spoken language evolved is likely to become clearer with concerted efforts in testing comparative data from many non-human animal species.

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    • "First, we can voluntarily and independently control the source and filter properties of our vocalizations, and second we can perform these modulations in the complete absence of an associated inducing experience or state333435. It is important to note that vocal control as defined above is a phenomenon distinct from vocal learning, which does not necessarily involve flexible manipulation of the vocal anatomy but rather entails the capacity to acquire or converge call types or entire vocal repertoires through imitation or learning [36,37]. The use of specific[ 5 1 _ T D $ D I F F ] and pre-existing vocalizations in different or novel contexts, and the ability to respond differentially to the vocalizations of others through experience, is considered distinct from vocal production learning, namely because these behaviors are present in a broader range of animals and are likely to require comparatively less complex neural control [38]. "
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    • "The robust nucleus of the arcopallium (RA) is a premotor nucleus in the VMP. RA receives inputs from HVC (used as a proper name) of the VMP and also receives inputs from the lateral magnocellular nucleus of anterior nidopallium (LMAN) of the anterior forebrain pathway (AFP) that is necessary for song learning and adult song variability [3]. RA projection neurons project to brainstem respiratory and vocal control nuclei to form a part of song premotor pathway [4]. "
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    • ", 2014 ) . The songbird HVC is similar to layers 2 and 3 neurons of primary motor cortex , and thereby possibly also to LMC ; songbird LMAN has a weak similarity to Broca ' s area that requires further investigation for confirmation ; DLM ( dorsolateral nucleus of the medial thalamus ) is most similar to the human anterior thalamus necessary for speech learning and production ( Jarvis , 2004 ; Petkov and Jarvis , 2012 ) . In this article I present a hypothesis on how foreign accents could be improved by optimizing variability in vocal learning brain circuits , followed by support for the hypothesis , drawing on the literature on variability in songbird vocal learning and variability in motor learning . "
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