22 results on '"Walker, Kerry M. M."'
Search Results
2. The perception and cortical processing of communication sounds
- Author
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Walker, Kerry M. M., King, Andrew J., and Schnupp, Jan
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617.7 ,Neuroscience ,Bioinformatics (life sciences) ,Computational Neuroscience ,Perception ,ferret ,hearing ,pitch ,timbre ,auditory cortex ,neural encoding ,psychophysics ,neurophysiology - Abstract
The neural processes used to extract perceptual features of vocal calls, and subsequently to re-integrate those features to form a coherent auditory object, are poorly understood. In this thesis, extracellular recordings were carried out in order to investigate how the temporal envelope, pitch, timbre and spatial location of communication sounds are represented by neurons in two core and three belt areas of ferret (Mustela putorius furo) auditory cortex. Potential neural underpinnings of auditory perception were tested using neurometric analysis to relate the reliability of neural responses to the performance of ferret and human listeners on psychophysical tasks. I found that human listeners' discrimination of the temporal envelopes of vocalization sounds matched the best neurometrics calculated from the temporal spiking patterns of ferret cortical neurons. Neurometric scores based on the spike rates of cortical neurons accounted for ferrets' discrimination of the pitch of artificial vowels. I show that most auditory cortical neurons are modulated by a number of stimulus features, rather than being tuned to only one feature. Neurons in the core auditory cortical fields often respond uniquely to particular combinations of pitch and timbre features, while those in belt regions respond more linearly to feature combinations. Subtle differences in the sensitivity of neurons to pitch, timbre and azimuthal cues were found across cortical areas and depths. These results suggest that auditory cortical neurons provide widely distributed representations of vocalizations, and a single neuron can often use combinations of spike rate and temporal spiking responses to encode multiple sound features.
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- 2008
3. Integrating information from different senses in the auditory cortex
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King, Andrew J. and Walker, Kerry M. M.
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- 2012
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4. Cortical adaptation to sound reverberation.
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Ivanov, Aleksandar Z., King, Andrew J., Willmore, Ben D. B., Walker, Kerry M. M., and Harper, Nicol S.
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- 2022
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5. Harmonic Training and the formation of pitch representation in a neural network model of the auditory brain
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Ahmad, Nasir, Higgins, Irina, Walker, Kerry M. M., and Stringer, Simon M.
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ComputingMethodologies_PATTERNRECOGNITION ,Competitive neural network ,Quantitative Biology::Neurons and Cognition ,Computer Science::Sound ,pitch identification ,Harmonic Training ,auditory brain ,unsupervised learning ,lcsh:Neurosciences. Biological psychiatry. Neuropsychiatry ,Original Research ,Neuroscience ,lcsh:RC321-571 - Abstract
Attempting to explain the perceptual qualities of pitch has proven to be, and remains, a difficult problem. The wide range of sounds which elicit pitch and a lack of agreement across neurophysiological studies on how pitch is encoded by the brain have made this attempt more difficult. In describing the potential neural mechanisms by which pitch may be processed, a number of neural networks have been proposed and implemented. However, no unsupervised neural networks with biologically accurate cochlear inputs have yet been demonstrated. This paper proposes a simple system in which pitch representing neurons are produced in a biologically plausible setting. Purely unsupervised regimes of neural network learning are implemented and these prove to be sufficient in identifying the pitch of sounds with a variety of spectral profiles, including sounds with missing fundamental frequencies and iterated rippled noises.
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- 2016
6. Global timing: a conceptual framework to investigate the neural basis of rhythm perception in humans and non-human species
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Geiser, Eveline, Walker, Kerry M. M., and Bendor, Daniel
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lcsh:Psychology ,tempo ,synfire chain ,grouping ,brain ,lcsh:BF1-990 ,Perspective Article ,fMRI ,Psychology ,music ,rhythm ,meter ,beat - Abstract
Timing cues are inarguably an essential feature of music. To understand how the brain gives rise to our experience of music we must appreciate how acoustical temporal patterns are integrated over the range of several seconds in order to extract global timing. In music perception, global timing comprises three distinct but often interacting percepts: temporal grouping, beat, and tempo. What directions may we take to further elucidate where and how the global timing of music is processed in the brain? The present review addresses this question and describes our current understanding of the neural basis of global timing perception.
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- 2014
7. Local and Global Spatial Organization of Interaural Level Difference and Frequency Preferences in Auditory Cortex.
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Panniello, Mariangela, King, Andrew J., Dahmen, Johannes C., and Walker, Kerry M. M.
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- 2018
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8. Spectral timbre perception in ferrets: Discrimination of artificial vowels under different listening conditions.
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Bizley, Jennifer K., Walker, Kerry M. M., King, Andrew J., and Schnupp, Jan W. H.
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TONE color (Music theory) , *FERRET , *AUDITORY perception , *VOWELS , *PHONETICS - Abstract
Spectral timbre is an acoustic feature that enables human listeners to determine the identity of a spoken vowel. Despite its importance to sound perception, little is known about the neural representation of sound timbre and few psychophysical studies have investigated timbre discrimination in non-human species. In this study, ferrets were positively conditioned to discriminate artificial vowel sounds in a two-alternative-forced-choice paradigm. Animals quickly learned to discriminate the vowel sound /u/ from /[variant_greek_epsilon]/ and were immediately able to generalize across a range of voice pitches. They were further tested in a series of experiments designed to assess how well they could discriminate these vowel sounds under different listening conditions. First, a series of morphed vowels was created by systematically shifting the location of the first and second formant frequencies. Second, the ferrets were tested with single formant stimuli designed to assess which spectral cues they could be using to make their decisions. Finally, vowel discrimination thresholds were derived in the presence of noise maskers presented from either the same or a different spatial location. These data indicate that ferrets show robust vowel discrimination behavior across a range of listening conditions and that this ability shares many similarities with human listeners. [ABSTRACT FROM AUTHOR]
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- 2013
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9. Neural Mechanisms for the Abstraction and Use of Pitch Information in Auditory Cortex.
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Xiaoqin Wang and Walker, Kerry M. M.
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AUDITORY cortex , *NEUROBIOLOGY , *BRAIN function localization , *NEURONS , *AUDITORY evoked response , *RHYTHM - Abstract
Experiments in animals have provided an important complement to human studies of pitch perception by revealing how the activity of individual neurons represents harmonic complex and periodic sounds. Such studies have shown that the acoustical parameters associ-ated with pitch are represented by the spiking responses of neurons in Al (primary auditory cortex) and various higher auditory cortical fields. The responses of these neurons are also modulated by the timbre of sounds. In marmosets, a distinct region on the low-frequency border of primary and non-primary auditory cortex may provide pitch tuning that generalizes across timbre classes. [ABSTRACT FROM AUTHOR]
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- 2012
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10. Multiplexed and Robust Representations of Sound Features in Auditory Cortex.
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Walker, Kerry M. M., Bizley, Jennifer K., King, Andrew J., and Schnupp, Jan W. H.
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MULTIPLEXING , *SOUNDS , *AUDITORY cortex , *AUDITORY perception , *NEURONS , *FERRETS as laboratory animals - Abstract
We can recognize the melody of a familiar song when it is played on different musical instruments. Similarly, an animal must be able to recognize a warning call whether the caller has a high-pitched female or a lower-pitched male voice, and whether they are sitting in a tree to the left or right. This type of perceptual invariance to \"nuisance\" parameters comes easily to listeners, but it isunknownwhether orhow such robust representations of sounds are formed at the level of sensory cortex. In this study, we investigate whether neurons in both core and belt areas of ferret auditory cortex can robustly represent the pitch, formant frequencies, or azimuthal location of artificial vowel sounds while the other two attributes vary. We found that the spike rates of the majority of cortical neurons that are driven by artificial vowels carry robust representations of these features, but the most informative temporal response windows differ from neuron to neuron and across five auditory cortical fields. Furthermore, individual neurons can represent multiple features of sounds unambiguously by independently modulating their spike rates within distinct time windows. Such multiplexing may be critical to identifying sounds that vary along more than one perceptual dimension. Finally, we observed that formant information is encoded in cortex earlier than pitch information, and we show that this time course matches ferrets' behavioral reaction time differences on a change detection task. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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11. Temporal Processing Performance, Reading Performance, and Auditory Processing Disorder in Learning-Impaired Children and Controls.
- Author
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Walker, Kerry M. M., Brown, David K., Scarff, Carrie, Watson, Charlene, Muir, Patricia, and Phillips, Dennis P.
- Abstract
Copyright of Canadian Journal of Speech-Language Pathology & Audiology is the property of Speech-Language & Audiology Canada and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2011
12. Sensitivity and Selectivity of Neurons in Auditory Cortex to the Pitch, Timbre, and Location of Sounds.
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Bizley, Jennifer K. and Walker, Kerry M. M.
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AUDITORY perception , *HEARING , *SOUNDS , *AUDITORY cortex , *NEURONS - Abstract
We are able to rapidly recognize and localize the many sounds in our environment. We can describe any of these sounds in terms of various independent “features” such as their loudness, pitch, or position in space. However, we still know surprisingly little about how neurons in the auditory brain, specifically the auditory cortex, might form representations of these perceptual characteristics from the information that the ear provides about sound acoustics. In this article, the authors examine evidence that the auditory cortex is necessary for processing the pitch, timbre, and location of sounds, and document how neurons across multiple auditory cortical fields might represent these as trains of action potentials. They conclude by asking whether neurons in different regions of the auditory cortex might not be simply sensitive to each of these three sound features but whether they might be selective for one of them. The few studies that have examined neural sensitivity to multiple sound attributes provide only limited support for neural selectivity within auditory cortex. Providing an explanation of the neural basis of feature invariance is thus one of the major challenges to sensory neuroscience obtaining the ultimate goal of understanding how neural firing patterns in the brain give rise to perception. [ABSTRACT FROM PUBLISHER]
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- 2010
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13. Neural Ensemble Codes for Stimulus Periodicity in Auditory Cortex.
- Author
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Bizley, Jennifer K., Walker, Kerry M. M., King, Andrew J., and Schnupp, Jan W. H.
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STIMULUS intensity , *AUDITORY cortex , *NEURONS , *FERRETS as laboratory animals , *NEUROPHYSIOLOGY - Abstract
We measured the responses of neurons in auditory cortex of male and female ferrets to artificial vowels of varying fundamental frequency (f0), or periodicity, and compared these with the performance of animals trained to discriminate the periodicity of these sounds. Sensitivity to f0 was found in all five auditory cortical fields examined, with most of those neurons exhibiting either low-pass or high-pass response functions. Only rarely was the stimulus dependence of individual neuron discharges sufficient to account for the discrimination performance of the ferrets. In contrast, when analyzed with a simple classifier, responses of small ensembles, comprising 3-61 simultaneously recorded neurons, often discriminated periodicity changes as well as the animals did. We examined four potential strategies for decoding ensemble responses: spike counts, relative first-spike latencies, a binary "spike or no-spike" code, and a spike-order code. All four codes represented stimulus periodicity effectively, and, surprisingly, the spike count and relative latency codes enabled an equally rapid readout, within 75 ms of stimulus onset. Thus, relative latency codes do not necessarily facilitate faster discrimination judgments. A joint spike count plus relative latency code was more informative than either code alone, indicating that the information captured by each measure was not wholly redundant. The responses of neural ensembles, but not of single neurons, reliably encoded f0 changes even when stimulus intensity was varied randomly over a 20 dB range. Because trained animals can discriminate stimulus periodicity across different sound levels, this implies that ensemble codes are better suited to account for behavioral performance. [ABSTRACT FROM AUTHOR]
- Published
- 2010
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14. Pitch discrimination by ferrets for simple and complex sounds.
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Walker, Kerry M. M., Schnupp, Jan W. H., Hart-Schnupp, Sheelah M. B., King, Andrew J., and Bizley, Jennifer K.
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ANIMAL sounds , *FERRET , *EUROPEAN polecat , *VOWELS , *PHONOLOGY - Abstract
Although many studies have examined the performance of animals in detecting a frequency change in a sequence of tones, few have measured animals’ discrimination of the fundamental frequency (F0) of complex, naturalistic stimuli. Additionally, it is not yet clear if animals perceive the pitch of complex sounds along a continuous, low-to-high scale. Here, four ferrets (Mustela putorius) were trained on a two-alternative forced choice task to discriminate sounds that were higher or lower in F0 than a reference sound using pure tones and artificial vowels as stimuli. Average Weber fractions for ferrets on this task varied from ∼20% to 80% across references (200–1200 Hz), and these fractions were similar for pure tones and vowels. These thresholds are approximately ten times higher than those typically reported for other mammals on frequency change detection tasks that use go/no-go designs. Naive human listeners outperformed ferrets on the present task, but they showed similar effects of stimulus type and reference F0. These results suggest that while non-human animals can be trained to label complex sounds as high or low in pitch, this task may be much more difficult for animals than simply detecting a frequency change. [ABSTRACT FROM AUTHOR]
- Published
- 2009
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15. Interdependent Encoding of Pitch, Timbre, and Spatial Location in Auditory Cortex.
- Author
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Bizley, Jennifer K., Walker, Kerry M. M., Silverman, Bernard W., King, Andrew J., and Schnupp, Jan W. H.
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AUDITORY cortex , *TEMPORAL lobe , *NEURONS , *SOUNDS , *INTONATION (Phonetics) - Abstract
Because we can perceive the pitch, timbre, and spatial location of a sound source independently, it seems natural to suppose that cortical processing of sounds might separate out spatial from nonspatial attributes. Indeed, recent studies support the existence of anatomically segregated "what" and "where" cortical processing streams. However, few attempts have been made to measure the responses of individual neurons in different cortical fields to sounds that vary simultaneously across spatial and nonspatial dimensions. We recorded responses to artificial vowels presented in virtual acoustic space to investigate the representations of pitch, timbre, and sound source azimuth in both core and belt areas of ferret auditory cortex. A variance decomposition technique was used to quantify the way in which altering each parameter changed neural responses. Most units were sensitive to two or more of these stimulus attributes. Although indicating that neural encoding of pitch, location, and timbre cues is distributed across auditory cortex, significant differences in average neuronal sensitivity were observed across cortical areas and depths, which could form the basis for the segregation of spatial and nonspatial cues at higher cortical levels. Some units exhibited significant nonlinear interactions between particular combinations of pitch, timbre, and azimuth. These interactions were most pronounced for pitch and timbre and were less commonly observed between spatial and nonspatial attributes. Such nonlinearities were most prevalent in primary auditory cortex, although they tended to be small compared with stimulus main effects. [ABSTRACT FROM AUTHOR]
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- 2009
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16. Linking Cortical Spike Pattern Codes to Auditory Perception.
- Author
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Walker, Kerry M. M., Ahmed, Bashir, and Schnupp, Jan W. H.
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AUDITORY perception , *PSYCHOMETRICS , *VISUAL cortex , *CEREBRAL cortex , *PATTERN perception , *SENSES , *BIOACOUSTICS - Abstract
Neurometric analysis has proven to be a powerful tool for studying links between neural activity and perception, especially in visual and somatosensory cortices, but conventional neurometrics are based on a simplistic rate-coding hypothesis that is clearly at odds with the rich and complex temporal spiking patterns evoked by many natural stimuli. In this study, we investigated the possible relationships between temporal spike pattern codes in the primary auditory cortex (A1) and the perceptual detection of subtle changes in the temporal structure of a natural sound. Using a two-alternative forced-choice oddity task, we measured the ability of human listeners to detect local time reversals in a marmoset twitter call. We also recorded responses of neurons in A1 of anesthetized and awake ferrets to these stimuli, and analyzed these responses using a novel neurometric approach that is sensitive to temporal discharge patterns. We found that although spike count-based neurometrics were inadequate to account for behavioral performance on this auditory task, neurometrics based on the temporal discharge patterns of populations of A1 units closely matched the psychometric performance curve, but only if the spiking patterns were resolved at temporal resolutions of 20 msec or better. These results demonstrate that neurometric discrimination curves can be calculated for temporal spiking patterns, and they suggest that such an extension of previous spike count-based approaches is likely to be essential for understanding the neural correlates of the perception of stimuli with a complex temporal structure. [ABSTRACT FROM AUTHOR]
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- 2008
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17. Distributed Sensitivity to Conspecific Vocalizations and Implications for the Auditory Dual Stream Hypothesis.
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Bizley, Jennifer K. and Walker, Kerry M. M.
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AUDITORY adaptation , *AUDITORY evoked response , *AUDITORY perception , *DIRECTIONAL hearing , *AUDITORY scene analysis , *ANIMAL sound production - Abstract
The article examines several studies on distributed sensitivity to conspecific vocalizations and its implications for the auditory dual stream hypothesis. It cites the findings of one study claiming that neurons across five cortical fields have similar degree of selectivity for monkey vocalizations. It suggests that the question of feature selectivity in auditory streams could be further evaluated by showing how independently the neural responses are encoded in the same neurons.
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- 2009
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18. Auditory cortex represents both pitch judgments and the corresponding acoustic cues.
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Bizley JK, Walker KM, Nodal FR, King AJ, and Schnupp JW
- Subjects
- Acoustic Stimulation, Animals, Female, Auditory Cortex physiology, Auditory Perception physiology, Cues, Ferrets physiology, Pitch Discrimination physiology, Synaptic Potentials physiology
- Abstract
The neural processing of sensory stimuli involves a transformation of physical stimulus parameters into perceptual features, and elucidating where and how this transformation occurs is one of the ultimate aims of sensory neurophysiology. Recent studies have shown that the firing of neurons in early sensory cortex can be modulated by multisensory interactions [1-5], motor behavior [1, 3, 6, 7], and reward feedback [1, 8, 9], but it remains unclear whether neural activity is more closely tied to perception, as indicated by behavioral choice, or to the physical properties of the stimulus. We investigated which of these properties are predominantly represented in auditory cortex by recording local field potentials (LFPs) and multiunit spiking activity in ferrets while they discriminated the pitch of artificial vowels. We found that auditory cortical activity is informative both about the fundamental frequency (F0) of a target sound and also about the pitch that the animals appear to perceive given their behavioral responses. Surprisingly, although the stimulus F0 was well represented at the onset of the target sound, neural activity throughout auditory cortex frequently predicted the reported pitch better than the target F0., (Copyright © 2013 Elsevier Ltd. All rights reserved.)
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- 2013
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19. Neural mechanisms for the abstraction and use of pitch information in auditory cortex.
- Author
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Wang X and Walker KM
- Subjects
- Acoustic Stimulation, Animals, Electrophysiology, Humans, Pitch Discrimination, Auditory Cortex physiology, Brain Mapping, Evoked Potentials, Auditory physiology, Pitch Perception physiology
- Abstract
Experiments in animals have provided an important complement to human studies of pitch perception by revealing how the activity of individual neurons represents harmonic complex and periodic sounds. Such studies have shown that the acoustical parameters associated with pitch are represented by the spiking responses of neurons in A1 (primary auditory cortex) and various higher auditory cortical fields. The responses of these neurons are also modulated by the timbre of sounds. In marmosets, a distinct region on the low-frequency border of primary and non-primary auditory cortex may provide pitch tuning that generalizes across timbre classes.
- Published
- 2012
- Full Text
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20. Auditory neuroscience: temporal anticipation enhances cortical processing.
- Author
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Walker KM and King AJ
- Subjects
- Animals, Auditory Pathways physiology, Rats, Sound, Acoustic Stimulation, Auditory Cortex physiology, Auditory Perception physiology
- Abstract
A recent study shows that expectation about the timing of behaviorally-relevant sounds enhances the responses of neurons in the primary auditory cortex and improves the accuracy and speed with which animals respond to those sounds., (Copyright © 2011 Elsevier Ltd. All rights reserved.)
- Published
- 2011
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21. Cortical encoding of pitch: recent results and open questions.
- Author
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Walker KM, Bizley JK, King AJ, and Schnupp JW
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- Acoustic Stimulation, Acoustics, Animals, Behavior, Animal, Humans, Models, Neurological, Periodicity, Auditory Cortex physiology, Pitch Perception physiology
- Abstract
It is widely appreciated that the key predictor of the pitch of a sound is its periodicity. Neural structures which support pitch perception must therefore be able to reflect the repetition rate of a sound, but this alone is not sufficient. Since pitch is a psychoacoustic property, a putative cortical code for pitch must also be able to account for the relationship between the amount to which a sound is periodic (i.e. its temporal regularity) and the perceived pitch salience, as well as limits in our ability to detect pitch changes or to discriminate rising from falling pitch. Pitch codes must also be robust in the presence of nuisance variables such as loudness or timbre. Here, we review a large body of work on the cortical basis of pitch perception, which illustrates that the distribution of cortical processes that give rise to pitch perception is likely to depend on both the acoustical features and functional relevance of a sound. While previous studies have greatly advanced our understanding, we highlight several open questions regarding the neural basis of pitch perception. These questions can begin to be addressed through a cooperation of investigative efforts across species and experimental techniques, and, critically, by examining the responses of single neurons in behaving animals., (© 2010 Elsevier B.V. All rights reserved.)
- Published
- 2011
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22. Development of perceptual correlates of reading performance.
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Walker KM, Hall SE, Klein RM, and Phillips DP
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- Adolescent, Adult, Age Factors, Child, Female, Humans, Linear Models, Male, Middle Aged, Phonetics, Time Factors, Auditory Perception physiology, Discrimination, Psychological physiology, Human Development, Reading, Visual Perception physiology
- Abstract
Performance on perceptual tasks requiring the discrimination of brief, temporally proximate or temporally varying sensory stimuli (temporal processing tasks) is impaired in some individuals with developmental language disorder and/or dyslexia. Little is known about how these temporal processes in perception develop and how they relate to language and reading performance in the normal population. The present study examined performance on 8 temporal processing tasks and 5 language/reading tasks in 120 unselected readers who varied in age over a range in which reading and phonological awareness were developing. Performance on all temporal processing tasks except coherent motion detection improved over ages 7 years to adulthood (p<0.01), especially between ages 7 and 13 years. Independent of these age effects, performance on all 8 temporal processing tasks predicted phonological awareness and reading performance (p<0.05), and three auditory temporal processing tasks predicted receptive language function (p<0.05). Furthermore, all temporal processing measures except within-channel gap detection and coherent motion detection predicted unique variance in phonological scores within subjects, whereas only within-channel gap detection performance explained unique variance in orthographic reading performance. These findings partially support the (Farmer, M.E., Klein, R.M., 1995. The evidence for a temporal processing deficit linked to dyslexia: A review. Psychon. Bull. Rev. 2, 460-493) notion of there being separable auditory and visual perceptual contributions to phonological and orthographic reading development. The data also are compatible with the view that the umbrella term "temporal processing" encompasses fundamentally different sensory or cognitive processes that may contribute differentially to language and reading performance, which may have different developmental trajectories and be differentially susceptible to pathology.
- Published
- 2006
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