Bharath Chandrasekaran

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 Research Interests

            I am currently a doctoral candidate in the interdisciplinary neuroscience program. The interdisciplinary neuroscience program is a conglomerate of several departments conducting neuroscience-related research, which could range from molecular to behavioral neuroscience. My primary or home department is Speech, Language, and Hearing sciences.  I am interested in understanding the nature and limits of experience-dependant plasticity in the early cortical processing of linguistically-relevant features of speech, as evidenced by event-related potentials.

            Recently, it has been shown that early cortical processing of speech, as reflected by the mismatch negativity (MMN) component, is a function of both acoustic dissimilarity and language experience. These findings suggest that experience-dependant plasticity enhances processing as early as 100-250 ms post change-onset, a time-window widely regarded to be ‘automatic’ and 'preattentive'. Crosslanguage studies have demonstrated experience-dependant plasticity for a number of features of speech processing, including consonants , phonotactics , and more recently suprasegmental features. 

            In Chandrasekaran et al. (2007), we examined crosslanguage differences in early cortical processing of Mandarin tones. We found that native speakers of Mandarin demonstrated larger MMN responses, relative to English speakers, for conditions that involved a contrast between level and contour tones. Since pitch is a multidimensional attribute, we conducted a companion study to determine the exact nature and number of dimensions or features that underlie the Mandarin electrophysiological tone space. We applied a three-way multidimensional scaling analysis (Individual Differences Scaling; INDSCAL) directly on the MMN mean amplitudes of individual subjects. We found that INDSCAL could indeed extract a common set of dimensions that underlie the group electrophysiological space. More importantly, individuals were found to differ in the relative weights placed on separate dimensions as a function of language experience.           

            By applying INDSCAL to ERP responses we now have a tool to explore the number and nature of neurocognitive dimensions underlying the MMN and their relative importance to one another as a function of one's auditory experience. We can now design comparable MMN paradigms to objectively evaluate the neural and behavioral effects of speech sound training, or retraining in the case of disordered populations. This gives us an objective method to quantify ‘learning’, since the MMN responses are free of potential confounds such as attention and memory which typically plague behavioral indices.

Recent Publications

Chandrasekaran, B., Gandour, J. T., & Krishnan, A. (in press). Neuroplasticity in the processing of pitch dimensions: A multidimensional scaling analysis of the mismatch negativity. Restorative Neurology and Neuroscience

Chandrasekaran, B., Krishnan, A., & Gandour, J. T. (2007). Mismatch negativity to pitch contours is influenced by language experience. Brain Research, 1128(1), 148-156.

Kemmerer, D., Chandrasekaran, B., & Tranel, D. (2007). A case of impaired verbalization but preserved gesticulation of motion events. Cognitive Neuropsychology 24 (1), 70-114.

Huber, J. E., & Chandrasekaran, B. (2006). Effects of increasing sound pressure level on lip and jaw movement parameters and consistency in young adults. J Speech Language and Hearing Research, 49(6), 1368-1379.

Huber, J. E., Chandrasekaran, B., & Wolstencroft, J. J. (2005). Changes to respiratory mechanisms during speech as a result of different cues to increase loudness. Journal of Applied Physiology, 98(6), 2177-2184

Presentations

Chandrasekaran, B., Gandour, J. T., & Krishnan, A. (2007, April). Crosslanguage differences in preattentive processing of pitch dimensions as revealed by multidimensional scaling analysis of the mismatch negativity. Poster to be presented at the Cognitive neuroscience society annual meeting.

Chandrasekaran, B., Gandour, J. T., & Krishnan, A. (2007, June). Neuroplasticity in the processing of pitch dimensions: A multidimensional scaling analysis of the mismatch negativity. Poster to be presented at the Organization for Human Brain Mapping Conference.

Chandrasekaran, B., Krishnan, A., & Gandour, J. T. (2006, April). Language experience modulates preattentive pitch processing: A crosslanguage study. Poster presented at the 4th Conference on Mismatch Negativity (MMN) and its Clinical and Scientific Applications.

Chandrasekaran, B., Krishnan, A., Swaminathan, J., & Gandour, J. T. (2006, February). Language-dependent preattentive pitch processing in young adults. Podium presentation at the Annual Meeting of the Association for Research in Otolaryngology, Baltimore.

Chandrasekaran, B., Kemmerer, D., & Tranel, D. (2005, April). A case of impaired verbalization but preserved gesticulation of motion events: Investigating the language-specific representation of space from a neuropsychological perspective. Poster presented at the Cognitive Neuroscience Society Annual Conference.

Chandrasekaran, B., & Huber, J. E. (2004, November). Young adults’ respiratory patterns and speech variability in noise. Podium presented at the American Speech-Language-Hearing Association Conference.