Processing acoustic communication signals is among the most difficult, yet vital capabilities that the auditory system must achieve. These abilities lie at the heart of language and speech processing, and their success or failure can have profound impacts on quality of life across the lifespan. Understanding the neurobiological mechanisms that support these basic abilities holds promise for advancing assistive listening devices, as well as improving diagnoses and treatments for learning disabilities and communication disorders such as auditory processing disorder, dyslexia, and specific language impairment. While much has been learned about the loci of language-related processing using non-invasive neuroscience techniques in humans, these techniques cannot answer how individual neurons and neural circuits implement language-relevant computations. As a result, the explicit cellular circuit-level and neuro-computational mechanisms that support acoustic communication signal processing are poorly understood. Multiple lines of research suggest that songbirds can provide an excellent model for investigating shared auditory processing abilities relevant to language, in particular the processing of temporal patterns within communication signals. The experiments outlined in this proposal investigate the neural mechanisms of auditory temporal pattern processing. In humans, the transition statistics between adjacent speech sounds (phonemes) can aid or alter phoneme categorization, providing cues for language learners and listeners to disambiguate perceptually similar sounds. Sensitivity to transition statistics is not exclusive to speech signals however, but reflects general auditory processes shared by many animals.
In Aim 1 we investigate the categorical perception of complex auditory objects in populations of cortical neurons in an animal model, and ask how these neural representations are effected by temporal context. In addition to which elements occur in a sequence, speech processing also requires knowing where those elements occur. Sensitivities to the statistical regularities of speech sequences are established long before infants learn to speak, and continue to affect both recognition and comprehension throughout adulthood. Studies in Aim 2 focus on how sequence-specific information is encoded by single neurons and neural populations in auditory cortex.
In Aim 3, we propose a basic circuit in which population level representations of auditory objects could be differentially modulated by patterning rules, and test this proposed pattern processing circuit using direct, casual manipulations. The proposed approach permits progress in the near term towards establishing the basic neurobiological substrates of foundational language-relevant abilities and a general framework within which more complex, uniquely human processes, can be proposed and eventually tested.
Normal speech comprehension and communication are rooted in basic auditory cognitive processes. Deficits in these processes accompany severe communication disorders (e.g. auditory processing disorder, dyslexia, specific language impairment, autism), and their abnormal function can compound the negative impacts of hearing impairments. The proposed project investigates the neuronal mechanisms of auditory temporal pattern processing using natural communication signals, with the ultimate goal of understanding the neurobiological basis of language-relevant abilities and improving treatment of communication processing disorders.
