Most natural acoustic sounds consist of multiple frequencies. An important auditory perceptual ability to resolve such acoustic properties is referred to as spectral processing and includes frequency resolution, frequency selectivity and spectral envelope perception. Frequency resolution, as demonstrated by masking techniques, indicates that our auditory system functions as an auditory filter bank with overlapping bandpass filters. These filters allow for the effective separation of sounds into different frequency bands or channels. Acoustic components that fall within a given filter or passband are considered to be processed “within channel” and are perceptually resolved using “local” spectral cues, whereas components in different passbands are processed “across channel” and perceived using “global” spectral cues. Spectral envelope perception is one aspect of spectral processing known to be important for segregating sounds in complex listening environments and relies on both local and global spectral cues. The purpose of this dissertation is to better understand how humans perceive and neurally encode perceptual cues associated with spectral envelope perception using spectral modulation detection tasks. This project addressed three primary aims; 1) characterize the effects of stimulus duration and level on behavioral detection of spectral modulation, 2) index neural encoding of global (i.e., spectral modulation frequency) versus local (i.e., carrier frequency) spectral cues and the role of selective attention to those cues during spectral modulation identification using cortical auditory evoked potentials (CAEP), and 3) quantify the relative weights of global and local cues using condition-on-a-single-stimulus (COSS) analysis with simultaneous CAEP recording in a spectral modulation identification task. The major results of the project show that 1) changes in both stimulus duration and presentation level impact spectral modulation detection thresholds, 2) CAEP components (N1, P2, LLP) are differentially modulated when attentional demands are varied, but spectral processing remains dominant in left hemisphere compared to right hemisphere regardless of attentional demands, and 3) individuals differentially place perceptual weights on both global and local cues, with CAEP responses reflecting those differences in weights and also being predictive of behavioral decisions on a trial-by-trial basis
