Vocal communication is important for human learning and social interaction. Speech perception impairments are features of neurological disorders such as auditory processing disorder (APD) and autism. In APD patients and some learning-disabled children, abnormalities in the neural processing of spectrotemporally complex sounds such as those in vocalizations are observed. The goal of this research is to understand how auditory learning (perception) and vocal learning (production) affect the neural processing of vocalizations and other sounds. Animals that learn to recognize and produce complex communication vocalizations are appropriate model systems in which to study how learning alters the neural coding of vocalizations. Songbirds are well suited for this research because: 1) they are highly skilled in auditory recognition learning;2) they learn to produce their own vocalizations by vocal imitation, like humans but unlike most other animals;and 3) the auditory brain regions that process vocalizations are known. Songbirds also produce different behavioral responses to vocalizations that differ in behavioral importance, or salience. In our model species, the zebra finch, auditory midbrain neurons produce robust and reliable responses to a wide range of sounds, including complex vocalizations. Studies will test three main hypotheses. First, auditory recognition learning alters the midbrain encoding of songs and other sounds (Aim 1). We will train adult birds to recognize and respond to specific songs and then compare the responses of midbrain neurons to recognizable songs and untrained songs. Predicted differences in the neural responses to recognizable and untrained songs are spike rate, neural discrimination, spectral tuning and spectrotemporal tuning. Second, the responses of midbrain neurons to vocalizations depend on the behavioral salience of vocalizations (Aim 2). We will train adult birds to associate positive or negative behavioral salience with specific songs, and then compare the responses of midbrain neurons to salient songs with positive and negative valence, and songs without trained salience. Third, song learning (learning to produce songs by imitation) alters midbrain encoding of songs (Aim 3). We will raise juvenile birds under conditions in which song learning does and does not occur, and compare the auditory responses of midbrain neurons from birds that have and have not learned to produce song. The proposed experiments will use behavioral training/testing, neurophysiology, computational data analysis, anatomical analysis, and manipulations in vocal learning to identify how learning shapes neuronal responses to communication vocalizations. Understanding the effects of auditory and vocal learning on sound coding in vocal learners may provide candidate neural mechanisms for how auditory training alters speech coding in the human brain and ideas about how speech acquisition shapes speech processing.
Deficits in vocal communication are hallmarks of human disorders such as auditory processing disorder (APD) and autism, and interfere with learning, social interactions and work productivity. The proposed research will test the effects of adult auditory learning and juvenile vocal learning on neuronal responses to vocalizations and other sounds in the auditory midbrain. The neural mechanisms of vocal perception that are described in this work may suggest candidate mechanisms for how auditory training alters human brain processing of speech sounds and how speech acquisition shapes speech processing.
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