My research is focused on the neural mechanisms involved in auditory processing in humans. I employ behavioral, electrophysiological (ERP), and neuroimaging (fMRI) techniques to explore auditory selective attention, speech processing, and cortical plasticity of auditory processing in adults and children with typical and atypical sensory experience. The goals of this research are to address several questions about auditory processing in the brain including: 1) How is auditory processing functionally subdivided in the human brain, 2) Are there differences in the plasticity profiles for auditory subsystems, 3) Are there relationships between the selection criteria listeners use to attend to specific auditory features and the mechanisms by which attention affects perception, 4) How do listeners learn to attend to the most informative features in auditory scenes, and 5) What is the role of auditory selective attention in speech processing by both children and adults?
Functional Subdivisions of Auditory Processing: Evidence that the same organizational principles apply to visual and auditory perception would suggest candidates for structure/ function relationships that apply to the entire brain. Current research in this area seeks to draw parallels between retinotopic and tonotopic organization, spatial processing in the two modalities, distinct dorsal and ventral processing streams for location and identity information, and differential processing of relatively local and global features along different dimensions in hierarchical stimuli. However, defining the features and types of information to be considered equivalent in the visual and auditory modalities has been controversial. Before drawing such parallels it will be necessary to apply the same techniques to auditory perception that were used to determine the functional divisions in the visual modality at the levels of ocular dominance columns, spatial receptive fields, orientation selectivity, motion processing, and more general ‘what’ and ‘where’ pathways.
Differential Plasticity in Auditory Subsystems: Within neural systems, there is ample evidence that some functions and underlying structures are shaped by experience throughout the life span, other subsystems have critical periods limiting the time windows in which experience has its largest effects, and still others are relatively impervious to the impact of experience. Detailed descriptions of the plasticity profiles for subsystems within auditory perception would provide information about what types of auditory experiences are important and when in development they are needed for individuals to attain normal auditory perceptual skills. Furthermore, any similarities between the types of structures and functions that share constraints on plasticity could point to possible mechanisms for that plasticity.
Auditory Selective Attention: Listeners can preferentially process sounds
based on location, range of frequencies, temporal characteristics, and
combinations of features. Precise definitions of exactly what listeners
can attend to would provide information about basic auditory features
as well as the nature of auditory objects. Attentional mechanisms can
be better understood through relationships between selection along different
dimensions and how attention modulates perceptual processing. Furthermore,
auditory selective attention is important for many other perceptual and
cognitive skills including speech processing, identifying sound sources
in noisy environments, and cross-modal perception. Both deficits and enhancements
in control of auditory attention are likely to impact individuals’
abilities in these other areas.
Lisa D. Sanders
Cognitive Neuroscience of Auditory Perception and Speech Processing
Attention in Speech Processing: Speech consists of an overwhelming number of rapid frequency and amplitude changes. Selective attention may help listeners to preferentially process the most informative features and segments in continuous speech streams. However, for attention to help people process speech, listeners have to learn which features and segments are in fact most informative and these parameters differ between languages. Both infants learning a language for the first time and children and adults learning a second language have to tune selective auditory attention to speech in a specific language. Research in this area will provide information about how experience shapes attentional selection criteria and the ways in which the efficiency of this selection is reflected in successful speech comprehension.
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