6 research outputs found
Auditory Perception and Neural Encoding of Spectral Modulation
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
Auditory Perception and Neural Encoding of Spectral Modulation
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
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Exponential spectro-temporal modulation generation.
Traditionally, real-time generation of spectro-temporally modulated noise has been performed on a linear amplitude scale, partially due to computational constraints. Experiments often require modulation that is sinusoidal on a logarithmic amplitude scale as a result of the many perceptual and physiological measures which scale linearly with exponential changes in the signal magnitude. A method is presented for computing exponential spectro-temporal modulation, showing that it can be expressed analytically as a sum over linearly offset sidebands with component amplitudes equal to the values of the modified Bessel function of the first kind. This approach greatly improves the efficiency and precision of stimulus generation over current methods, facilitating real-time generation for a broad range of carrier and envelope signals
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Exponential spectro-temporal modulation generation.
Traditionally, real-time generation of spectro-temporally modulated noise has been performed on a linear amplitude scale, partially due to computational constraints. Experiments often require modulation that is sinusoidal on a logarithmic amplitude scale as a result of the many perceptual and physiological measures which scale linearly with exponential changes in the signal magnitude. A method is presented for computing exponential spectro-temporal modulation, showing that it can be expressed analytically as a sum over linearly offset sidebands with component amplitudes equal to the values of the modified Bessel function of the first kind. This approach greatly improves the efficiency and precision of stimulus generation over current methods, facilitating real-time generation for a broad range of carrier and envelope signals
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Temporal integration of monaural and dichotic frequency modulation.
Frequency modulation (FM) detection at low modulation frequencies is commonly used as an index of temporal fine-structure processing. The present study evaluated the rate of improvement in monaural and dichotic FM across a range of test parameters. In experiment I, dichotic and monaural FM detection was measured as a function of duration and modulator starting phase. Dichotic FM thresholds were lower than monaural FM thresholds and the modulator starting phase had no effect on detection. Experiment II measured monaural FM detection for signals that differed in modulation rate and duration such that the improvement with duration in seconds (carrier) or cycles (modulator) was compared. Monaural FM detection improved monotonically with the number of modulation cycles, suggesting that the modulator is extracted prior to detection. Experiment III measured dichotic FM detection for shorter signal durations to test the hypothesis that dichotic FM relies primarily on the signal onset. The rate of improvement decreased as duration increased, which is consistent with the use of primarily onset cues for the detection of dichotic FM. These results establish that improvement with duration occurs as a function of the modulation cycles at a rate consistent with the independent-samples model for monaural FM, but later cycles contribute less to detection in dichotic FM