Monty Escabi, Ph.D.
Assistant Professor
Electrical and Computer Engineering, Biomedical Engineering
University of Connecticut
Abstract:
Ascending information from brainstem structures converges in the central nucleus of the inferior colliculus (ICC) and is rerouted to the primary auditory cortex (AI) via the auditory thalamus (MGBv). This hierarchical organization leads to a significant reduction in temporal modulation preferences from the ICC to AI. Neurons in the ICC, MGBv and AI also exhibit significant selectivity to spectral, intensity, and aural dimensions of complex stimuli; however, how these neural stations simultaneously process all of these stimulus dimensions and cues is not clear. A spectro-temporal Gabor analysis technique is presented that we are using to study joint spectro-temporal preferences in these neuronal stations and which we are using to characterize the transformations incurred at each level of processing. We use this technique to characterize the interrelationships, trade-offs, and differences between temporal, spectral and aural aspects of processing. Comparisons of auditory spectro-temporal receptive fields (STRFs) in the ICC, MGBv, and AI shows relative conservation of spectral modulation preferences but a large shift in preferred temporal modulations, as previously described with sinusoidal AM. Temporal modulation transfer functions are significantly overlapped in the thalamus and AI, although they extend to higher modulation rates in the ICC. A novel trade-off in spectral and temporal modulation preferences is seen only at the level of the ICC. Aural selectivities are explored via comparisons of left versus right ear STRFs. We are finding that the binaural structure of the auditory STRF is adept to a spectro-temporal binaural disparity analysis, analogous to the spatio-temporal binocular disparity analysis proposed by Anzai et al. for processing motion and depth in the primary visual cortex. Such a joint analysis of spectro-temporal and binaural information may enable auditory neurons to simultaneously and independently encode head related spatial cues and contextual information found in complex environmental stimuli.