Browsing by Subject "auditory"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Data supporting Lung-to-ear sound transmission does not improve directional hearing in green treefrogs (Hyla cinerea)(2020-09-04) Christensen-Dalsgaard, Jakob; Lee, Norman; Bee, Mark A; mbee@umn.edu; Bee, Mark AAmphibians are unique among extant vertebrates in having middle ear cavities that are internally coupled to each other and to the lungs. In frogs, the lung-to-ear sound transmission pathway can influence the tympanum’s inherent directionality, but what role such effects might play in directional hearing remain unclear. In this study of the American green treefrog (Hyla cinerea), we tested the hypothesis that the lung-to-ear sound transmission pathway functions to improve directional hearing, particularly in the context of intraspecific sexual communication. Using laser vibrometry, we measured the tympanum’s vibration amplitude in females in response to a frequency modulated sweep presented from 12 sound incidence angles in azimuth. Tympanum directionality was determined across three states of lung inflation (inflated, deflated, reinflated) both for a single tympanum in the form of the vibration amplitude difference (VAD) and for binaural comparisons in the form of the interaural vibration amplitude difference (IVAD). The state of lung inflation had negligible effects (typically less than 0.5 dB) on both VADs and IVADs at frequencies emphasized in the advertisement calls produced by conspecific males (834 Hz and 2730 Hz). Directionality at the peak resonance frequency of the lungs (1558 Hz) was improved by ≅ 3 dB for a single tympanum when the lungs were inflated versus deflated, but IVADs were not impacted by the state of lung inflation. Based on these results, we reject the hypothesis that the lung-to-ear sound transmission pathway functions to improve directional hearing in frogs.Item Perception and Processing of Pitch and Timbre in Human Cortex(2018-04) Allen, EmilyPitch and timbre are integral components of auditory perception, yet our understanding of how they interact with one another and how they are processed cortically is enigmatic. Through a series of behavioral studies, neuroimaging, and computational modeling, we investigated these attributes. First, we looked at how variations in one dimension affect our perception of the other. Next, we explored how pitch and timbre are processed in the human cortex, in both a passive listening context and in the presence of attention, using univariate and multivariate analyses. Lastly, we used encoding models to predict cortical responses to timbre using natural orchestral sounds. We found that pitch and timbre interact with each other perceptually, and that musicians and non-musicians are similarly affected by these interactions. Our fMRI studies revealed that, in both passive and active listening conditions, pitch and timbre are processed in largely overlapping regions. However, their patterns of activation are separable, suggesting their underlying circuitry within these regions is unique. Finally, we found that a five-feature, subjectively derived encoding model could predict a significant portion of the variance in the cortical responses to timbre, suggesting our processing of timbral dimensions may align with our perceptual categorizations of them. Taken together, these findings help clarify aspects of both our perception and processing of pitch and timbre.Item Perception of complex sounds at high frequencies(2022-05) Guest, DanielUnderstanding how the auditory system processes frequency and intensity information is crucial to our understanding of overall auditory function. Although great progress has been made in understanding this issue in the case of simple sounds, such as pure tones, considerable uncertainty remains in understanding how the auditory system processes frequency and intensity information in more complex and naturalistic sounds. Moreover, much of our understanding comes from sounds in the low-frequency range, where phase locking to temporal fine structure is available in the auditory nerve. To address these limitations, this dissertation first presents new data on a variety of psychoacoustical tasks measuring frequency and intensity perception not only at low frequencies but also at high frequencies. Next, the psychophysical results are interpreted with the aid of modern computational models of the auditory system, which capture key features of the complex and nonlinear processing that takes place in the auditory periphery and auditory subcortex. Both the behavioral and computational results demonstrate how perception of complex sound features, such as pitch and spectral shape, reflects a delicate combination of both low-level constraints imposed by peripheral encoding of sound and higher-level influences, such as central processing, familiarity, and context.