Kyle P. Walsh

Overshoot measured physiologically and psychophysically in the same human ears

A nonlinear version of the stimulus-frequency otoacoustic emission (SFOAE) was measured using stimulus waveforms similar to those used for behavioral overshoot. Behaviorally, the seven listeners were as much as 11 dB worse at detecting a brief tonal signal (4.0 kHz, 10 ms in duration) when it occurred soon after the onset of a wideband masking noise (0.1-6.0 kHz; 400 ms in duration) than when it was delayed by about 200 ms, and the nonlinear SFOAE measure exhibited a similar effect. When either lowpass (0.1-3.8 kHz) or bandpass noise (3.8-4.2 kHz) was used instead of the wideband noise, the physiological and behavioral measures again were similar. When a highpass noise (4.2-6.0 kHz) was used, the physiological and behavioral measures both showed no overshoot-like effect for five of the subjects. The physiological response to the tone decayed slowly after the termination of the noise, much like the time course of resetting for behavioral overshoot. One subject exhibited no overshoot behaviorally even though his cochlear responses were like those of the other subjects. Overall, the evidence suggests that some basic characteristics of overshoot are obligatory consequences of cochlear function, as modulated by the olivocochlear efferent system.

Properties of a nonlinear version of the stimulus-frequency otoacoustic emission

A procedure for extracting the nonlinear component of the stimulus-frequency otoacoustic emission (SFOAE) is described. This nSFOAE measures the amount by which the cochlear response deviates from linear additivity when the input stimulus is doubled in amplitude. When a 4.0-kHz tone was presented alone, the magnitude of the nSFOAE response remained essentially constant throughout the 400-ms duration of the tone; response magnitude did increase monotonically with increasing tone level. When a wideband noise was presented alone, nSFOAE magnitude increased over the initial 100- to 200-ms portion of the 400-ms duration of the noise. When the tone and the wideband noise were presented simultaneously, nSFOAE magnitude decreased momentarily, then increased substantially for about the first 100 ms and then remained strong for the remainder of the presentation. Manipulations of the noise bandwidth revealed that the low-frequency components were primarily responsible for this rising, dynamic response; no rising segment was seen with bandpass or highpass noise. The rising, dynamic nSFOAE response is likely attributable to activation of the medial olivocochlear efferent system. This perstimulatory emission appears to have the potential to provide information about the earliest stages of auditory processing for stimuli commonly used in psychoacoustical tasks.

Changes in otoacoustic emissions during selective auditory and visual attention

Previous studies have demonstrated that the otoacoustic emissions (OAEs) measured during behavioral tasks can have different magnitudes when subjects are attending selectively or not attending. The implication is that the cognitive and perceptual demands of a task can affect the first neural stage of auditory processing-the sensory receptors themselves. However, the directions of the reported attentional effects have been inconsistent, the magnitudes of the observed differences typically have been small, and comparisons across studies have been made difficult by significant procedural differences. In this study, a nonlinear version of the stimulus-frequency OAE (SFOAE), called the nSFOAE, was used to measure cochlear responses from human subjects while they simultaneously performed behavioral tasks requiring selective auditory attention (dichotic or diotic listening), selective visual attention, or relative inattention. Within subjects, the differences in nSFOAE magnitude between inattention and attention conditions were about 2-3 dB for both auditory and visual modalities, and the effect sizes for the differences typically were large for both nSFOAE magnitude and phase. These results reveal that the cochlear efferent reflex is differentially active during selective attention and inattention, for both auditory and visual tasks, although they do not reveal how attention is improved when efferent activity is greater.

Selective attention reduces physiological noise in the external ear canals of humans. I: Auditory attention

In this study, a nonlinear version of the stimulus-frequency OAE (SFOAE), called the nSFOAE, was used to measure cochlear responses from human subjects while they simultaneously performed behavioral tasks requiring, or not requiring, selective auditory attention. Appended to each stimulus presentation, and included in the calculation of each nSFOAE response, was a 30-ms silent period that was used to estimate the level of the inherent physiological noise in the ear canals of our subjects during each behavioral condition. Physiological-noise magnitudes were higher (noisier) for all subjects in the inattention task, and lower (quieter) in the selective auditory-attention tasks. These noise measures initially were made at the frequency of our nSFOAE probe tone (4.0 kHz), but the same attention effects also were observed across a wide range of frequencies. We attribute the observed differences in physiological-noise magnitudes between the inattention and attention conditions to different levels of efferent activation associated with the differing attentional demands of the behavioral tasks. One hypothesis is that when the attentional demand is relatively great, efferent activation is relatively high, and a decrease in the gain of the cochlear amplifier leads to lower-amplitude cochlear activity, and thus a smaller measure of noise from the ear.

Evidence for dynamic cochlear processing in otoacoustic emissions and behavior.

Psychophysical research suggests that active cochlear processing may partially explain temporal effects observed in certain auditory masking tasks [Strickland (2001), (2004)]. To investigate this possibility, this study examined the relationship between subjects’ psychophysical performance and the responses of their cochleas to the same stimulus waveforms. Stimulus‐frequency otoacoustic emissions (SFOAEs) were recorded in the ear canal using a nonlinear procedure. The results showed that the nonlinear SFOAE to a brief tonal signal (4 kHz, 10 ms, 60 dB SPL) in a background noise (100–6000 Hz, 400 ms, 25 dB/Hz) increased in magnitude (with signal delay) over a similar time course to subjects’ improvement psychophysically in detecting the same signal. Manipulation of the noise bandwidth revealed that the increases in SFOAE magnitude and the improvement in psychophysical detection both were caused primarily by off‐frequency components of the noise: lowpass components for SFOAEs, and lowpass or highpass compon...

Time-course of recovery from the effects of a notched-noise on the ear-canal pressure at different frequencies

Different methods for estimating the effect of the medial olivocochlear reflex (MOCR) on stimulus-frequency otoacoustic emissions (SFOAEs) in humans appear to yield different estimates of the time-course of recovery from the effect. However, it is uncertain whether the observed differences in recovery times were due to differences in the methods used to extract the changes in SFOAEs, due to the fact that different feedback-based reflexes—MOCR or the middle ear muscle reflex (MEMR)—were activated, or due to the dependence of recovery from the activated reflex on the probe frequency. In this study, the ear-canal pressure was measured for continuous probes with frequencies of 1, 2, 4, and 6 kHz, in the presence and absence of an ipsilateral notched-noise elicitor. Changes in the magnitude and phase of the ear-canal pressure were extracted to estimate recovery times from the effects of the elicitor. The results showed that the recovery time increased with increasing probe frequency—from about 380 ms at 1 kHz ...

Does the efferent system aid with selective attention

To study whether attention and inattention lead to differential activation of the olivocochlear (OC) efferent system, a cochlear measure of efferent activity was collected while human subjects performed behaviorally under the two conditions. Listeners heard two independent, simultaneous strings of seven digits, one spoken by a male and the other by a female, and at the end of some trials (known in advance), they were required to recognize the middle five digits spoken by the female. Interleaved with the digits were one stimulus that evokes a stimulus-frequency otoacoustic emission (SFOAE) and another that activates the OC system—a 4-kHz tone (60 dB SPL, 300 ms in duration) and a wideband noise (1.0–6.0 kHz, 25 dB spectrum level, 250 ms in duration, beginning 50 ms after tone onset). These interleaved sounds, used with a double-evoked procedure, permitted the collection of a nonlinear measure called the nSFOAE. When selective attention was required behaviorally, the magnitude of the nSFOAE to tone-plus-noi...

Research paperSelective attention reduces physiological noise in the external ear canals of humans. I: Auditory attention

In this study, a nonlinear version of the stimulus-frequency OAE (SFOAE), called the nSFOAE, was used to measure cochlear responses from human subjects while they simultaneously performed behavioral tasks requiring, or not requiring, selective auditory attention. Appended to each stimulus presentation, and included in the calculation of each nSFOAE response, was a 30-ms silent period that was used to estimate the level of the inherent physiological noise in the ear canals of our subjects during each behavioral condition. Physiological-noise magnitudes were higher (noisier) for all subjects in the inattention task, and lower (quieter) in the selective auditory-attention tasks. These noise measures initially were made at the frequency of our nSFOAE probe tone (4.0 kHz), but the same attention effects also were observed across a wide range of frequencies. We attribute the observed differences in physiological-noise magnitudes between the inattention and attention conditions to different levels of efferent activation associated with the differing attentional demands of the behavioral tasks. One hypothesis is that when the attentional demand is relatively great, efferent activation is relatively high, and a decrease in the gain of the cochlear amplifier leads to lower-amplitude cochlear activity, and thus a smaller measure of noise from the ear.

Selective attention reduces physiological noise in the external ear canals of humans. II

In this study, a nonlinear version of the stimulus-frequency OAE (SFOAE), called the nSFOAE, was used to measure cochlear responses from human subjects while they simultaneously performed behavioral tasks requiring, or not requiring, selective auditory attention. Appended to each stimulus presentation, and included in the calculation of each nSFOAE response, was a 30-ms silent period that was used to estimate the level of the inherent physiological noise in the ear canals of our subjects during each behavioral condition. Physiological-noise magnitudes were higher (noisier) for all subjects in the inattention task, and lower (quieter) in the selective auditory-attention tasks. These noise measures initially were made at the frequency of our nSFOAE probe tone (4.0 kHz), but the same attention effects also were observed across a wide range of frequencies. We attribute the observed differences in physiological-noise magnitudes between the inattention and attention conditions to different levels of efferent activation associated with the differing attentional demands of the behavioral tasks. One hypothesis is that when the attentional demand is relatively great, efferent activation is relatively high, and a decrease in the gain of the cochlear amplifier leads to lower-amplitude cochlear activity, and thus a smaller measure of noise from the ear.

Cochlear measures of selective auditory attention.

The possibility that selective auditory attention can affect the responses of the cochlea via the medial olivocochlear (MOC) pathway was investigated in human listeners using a nonlinear version of the stimulus‐frequency otoacoustic emission (SFOAE), called the nSFOAE [Walsh et al. (2010)]. During nSFOAE recording, listeners attended to one of two competing speech streams, each composed of seven randomly‐selected spoken digits that were interleaved with the nSFOAE stimuli. The talker was female in one ear and male in the other (randomized across trials). The task of the listener was to match a subset of the digits spoken by the female talker to one of two choices presented visually on a computer screen. The nSFOAE stimulus was a tone (4.0 kHz, 200 ms) presented simultaneously to the two ears, either in quiet (tone‐alone) or in noise (tone‐plus‐noise). When nSFOAEs were measured during periods of selective attention, the tone‐plus‐noise responses exhibited larger maximum magnitudes, and larger changes from the tone‐alone magnitudes, compared to the responses measured during a no‐attention condition, in which the competing speech streams were presented, but with no digit‐matching required. The differences in magnitudes across conditions were as much as 4–5 dB. [Work supported by the NIDCD.]