Welcome to the Ramachandran lab website! Our research focuses on auditory perception in normal and hearing-impaired subjects, the neuronal encoding of the sounds driving the percept in these subjects during behavioral performance, and the relationship between the encoding of sounds by the neurons and the perception of the subjects. Our studies use the nonhuman primate animal model with interest in perception in complex, realistic environments and the perception of complex stimuli.
Our lab is broadly interested in how individuals hear and process sounds, specifically in noisy, natural environments. Hearing in noise is a very challenging task, which is compromised in the elderly and the hearing impaired. The ability to hear in noise is not recovered even with hearing aids and cochlear implants.
We investigate the changes in the auditory system and their locus after hearing loss or as a consequence of aging. Our studies characterize normal-hearing subjects’ behavioral performance and the underlying neuronal correlates related to the detection of sounds in noise. We also investigate neuronal encoding in subjects with hearing impairment. Electrophysiological tools allow us to directly correlate hearing metrics with neuronal activity in different parts of the brain. We can then use computational modeling to infer the auditory circuitry that could be influencing behavioral performance.The objectives of these studies are to compare the behavioral, anatomical, physiological, and neurochemical underpinnings of the normal performance with the performance of subjects with hearing impairment.
Our lab also investigates why some humans with no overt indications of hearing loss have difficulty processing speech in noisy environments. Recent animal evidence provides a potential explanation: a loss of ribbon synapses (synaptopathy) in the absence of cochlear hair cell loss, leading to a loss of auditory nerve fibers (ANFs). We examine synaptopathy by undertaking noninvasive studies to quantify physiological and perceptual abilities in subjects with clinically normal hearing thresholds, comparing noise-exposed (expected to have a higher prevalence and greater severity of synaptopathy markers) and control groups. With these studies, we aim to assess effects of noise exposure on temporal coding and behavioral sensitivity to temporal cues. We also wish to determine whether or not synaptopathy explains the patterns of physiological and behavioral measures we see in subjects who have difficulty processing sounds in noisy environments.