The Interaction of Bottom-up and Top-down Information in Human Auditory Learning and Object Recognition

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Object recognition is a crucial cognitive task for all sensory modalities. A particular challenge in object recognition is that physically dissimilar stimuli can have the same label (e.g., the same word spoken by different people, or the same face viewed under different lighting conditions), while physically similar stimuli may be labeled differently (e.g., hearing "b" or "p" based on small differences on when the vocal folds start vibrating). In audition, various animal species, but especially humans, have developed an elaborate system for communication based on the discrimination of fine acoustic differences between complex sounds. Speech perception is probably the most remarkable achievement in this domain and one that may influence the overall architecture of auditory cortex. The underlying neural mechanisms are poorly understood, however. With support from the National Science Foundation, Maximilian Riesenhuber and Josef P. Rauschecker of Georgetown University will address this issue by integrating behavioral results with functional magnetic resonance imaging (fMRI) measures of brain activity. The team will apply the insights gained in understanding the neural bases of visual object recognition to auditory object recognition. One study will investigate the neural mechanisms underlying the categorization and discrimination of speech sounds as well as the transformation of bottom-up acoustic information into categorical phonetic information along the cortical auditory hierarchy. The second study will investigate neuronal plasticity in auditory object recognition by training humans on an auditory categorization task involving modified monkey communication calls. By using novel yet natural auditory communication sounds, the investigators will be able to study the interaction of acoustic information and category labeling during learning and during recognition. The findings will be relevant for the understanding of higher-level auditory processing but also for a general understanding of the interactions between sensory and task-specific information in the brain as well as the commonalities and differences in the mechanisms supporting recognition of speech and non-speech sounds in the brain.Understanding the general principles of sensory processing in the brain, and in particular identifying the underlying neural mechanisms across sensory modalities, has implications for education (e.g., second language learning) and in engineering (e.g., the development of neurally-inspired speech recognition systems). The research project will also help train the next generation of scientists, at the graduate and undergraduate level, with a particular focus on underrepresented minorities. At the graduate level, the project directly involves graduate students from Georgetown University's Interdisciplinary PhD Program in Neuroscience, both at the thesis level and for introductory lab rotations. The project will further impact undergraduate education at Georgetown and beyond, with the opportunity for undergraduates to participate in the project as part of their cognitive science curriculum, or during summer internships. The summer outreach program for undergraduate students has a strong focus on minority recruitment through a partnership with Howard University in Washington, DC.