Speech-evoked activity in primary auditory cortex: effects of voice onset time

Voice onset time (VOT) is an important parameter of speech that denotes the time interval between consonant onset and the onset of low-frequency periodicity generated by rhythmic vocal cord vibration. Voiced stop consonants (/b/, /g/, and /d/) in syllable initial position are characterized by short VOTs, whereas unvoiced stop consonants (/p/, /k/, and t/) contain prolonged VOTs. As the VOT is increased in incremental steps, perception rapidly changes from a voiced stop consonant to an unvoiced consonant at an interval of 20–40 ms. This abrupt change in consonant identification is an example of categorical speech perception and is a central feature of phonetic discrimination. This study tested the hypothesis that VOT is represented within auditory cortex by transient responses time-locked to consonant and voicing onset. Auditory evoked potentials (AEPs) elicited by stop consonant-vowel (CV) syllables were recorded directly from Heschl's gyrus, the planum temporale, and the superior temporal gyrus in three patients undergoing evaluation for surgical remediation of medically intractable epilepsy. Voiced CV syllables elicited a triphasic sequence of field potentials within Heschl's gyrus. AEPs evoked by unvoiced CV syllables contained additional response components time-locked to voicing onset. Syllables with a VOT of 40, 60, or 80 ms evoked components time-locked to consonant release and voicing onset. In contrast, the syllable with a VOT of 20 ms evoked a markedly diminished response to voicing onset and elicited an AEP very similar in morphology to that evoked by the syllable with a 0-ms VOT. Similar response features were observed in the AEPs evoked by click trains. In this case, there was a marked decrease in amplitude of the transient response to the second click in trains with interpulse intervals of 20–25 ms. Speech-evoked AEPs recorded from the posterior superior temporal gyrus lateral to Heschl's gyrus displayed comparable response features, whereas field potentials recorded from three locations in the planum temporale did not contain components time-locked to voicing onset. This study demonstrates that VOT at least partially is represented in primary and specific secondary auditory cortical fields by synchronized activity time-locked to consonant release and voicing onset. Furthermore, AEPs exhibit features that may facilitate categorical perception of stop consonants, and these response patterns appear to be based on temporal processing limitations within auditory cortex. Demonstrations of similar speech-evoked response patterns in animals support a role for these experimental models in clarifying selected features of speech encoding.

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Spontaneous activity resembling tone-evoked activity in the primary auditory cortex of guinea pigs

Neuroscience Research ◽

10.1016/j.neures.2010.06.009 ◽

2010 ◽

Vol 68 (2) ◽

pp. 107-113 ◽

Cited By ~ 2

Author(s):

Kazuya Saitoh ◽

Shinji Inagaki ◽

Masataka Nishimura ◽

Hideo Kawaguchi ◽

Wen-Jie Song

Keyword(s):

Auditory Cortex ◽

Spontaneous Activity ◽

Guinea Pigs ◽

Primary Auditory Cortex ◽

Evoked Activity

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Dissociation of task engagement and arousal effects in auditory cortex and midbrain

eLife ◽

10.7554/elife.60153 ◽

2021 ◽

Vol 10 ◽

Author(s):

Daniela Saderi ◽

Zachary P Schwartz ◽

Charles R Heller ◽

Jacob R Pennington ◽

Stephen V David

Keyword(s):

Auditory Cortex ◽

Auditory Processing ◽

Generalized Linear Model ◽

Pupil Size ◽

Primary Auditory Cortex ◽

Task Engagement ◽

State Variables ◽

Neural Populations ◽

Evoked Activity ◽

Sensory Neural

Both generalized arousal and engagement in a specific task influence sensory neural processing. To isolate effects of these state variables in the auditory system, we recorded single-unit activity from primary auditory cortex (A1) and inferior colliculus (IC) of ferrets during a tone detection task, while monitoring arousal via changes in pupil size. We used a generalized linear model to assess the influence of task engagement and pupil size on sound-evoked activity. In both areas, these two variables affected independent neural populations. Pupil size effects were more prominent in IC, while pupil and task engagement effects were equally likely in A1. Task engagement was correlated with larger pupil; thus, some apparent effects of task engagement should in fact be attributed to fluctuations in pupil size. These results indicate a hierarchy of auditory processing, where generalized arousal enhances activity in midbrain, and effects specific to task engagement become more prominent in cortex.

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Pupil-associated states modulate excitability but not stimulus selectivity in primary auditory cortex

10.1101/619619 ◽

2019 ◽

Cited By ~ 1

Author(s):

Zachary P. Schwartz ◽

Brad N. Buran ◽

Stephen V. David

Keyword(s):

Auditory Cortex ◽

Cortical Neurons ◽

Pupil Size ◽

Large Scale ◽

Primary Auditory Cortex ◽

Neuron Activity ◽

Auditory Neurons ◽

Network State ◽

Pupil Constriction ◽

Evoked Activity

AbstractRecent research in mice indicates that luminance-independent fluctuations in pupil size predict variability in spontaneous and evoked activity of single neurons in auditory and visual cortex. These findings suggest that pupil is an indicator of large-scale changes in arousal state that affect sensory processing. However, it is not known whether pupil-related state also influences the selectivity of auditory neurons. We recorded pupil size and single-unit spiking activity in the primary auditory cortex (A1) of non-anesthetized male and female ferrets during presentation of natural vocalizations and tone stimuli that allow measurement of frequency and level tuning. Neurons showed a systematic increase in both spontaneous and sound-evoked activity when pupil was large, as well as desynchronization and a decrease in trial-to-trial variability. Relationships between pupil size and firing rate were non-monotonic in some cells. In most neurons, several measurements of tuning, including acoustic threshold, spectral bandwidth, and best frequency, remained stable across large changes in pupil size. Across the population, however, there was a small but significant decrease in acoustic threshold when pupil was dilated. In some recordings, we observed rapid, saccade-like eye movements during sustained pupil constriction, which may indicate sleep. Including the presence of this state as a separate variable in a regression model of neural variability accounted for some, but not all, of the variability and non-monotonicity associated with changes in pupil size.New & NoteworthyCortical neurons vary in their response to repeated stimuli, and some portion of the variability is due to fluctuations in network state. By simultaneously recording pupil and single-neuron activity in auditory cortex of ferrets, we provide new evidence that network state affects the excitability of auditory neurons, but not sensory selectivity. In addition, we report the occurrence of possible sleep states, adding to evidence that pupil provides an index of both sleep and physiological arousal.

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