Ann Clock Eddins

Evoked-potential changes following discrimination learning involving complex sounds

OBJECTIVE Perceptual sensitivities are malleable via learning, even in adults. We trained adults to discriminate complex sounds (periodic, frequency-modulated sweep trains) using two different training procedures, and used psychoacoustic tests and evoked potential measures (the N1-P2 complex) to assess changes in both perceptual and neural sensitivities. METHODS Training took place either on a single day, or daily across eight days, and involved discrimination of pairs of stimuli using a single-interval, forced-choice task. In some participants, training started with dissimilar pairs that became progressively more similar across sessions, whereas in others training was constant, involving only one, highly similar, stimulus pair. RESULTS Participants were better able to discriminate the complex sounds after training, particularly after progressive training, and the evoked potentials elicited by some of the sounds increased in amplitude following training. Significant amplitude changes were restricted to the P2 peak. CONCLUSIONS Our findings indicate that changes in perceptual sensitivities parallel enhanced neural processing. SIGNIFICANCE These results are consistent with the proposal that changes in perceptual abilities arise from the brains capacity to adaptively modify cortical representations of sensory stimuli, and that different training regimens can lead to differences in cortical sensitivities, even after relatively short periods of training.

Perceptions of Speech-Language Pathologists Linked to Evidence-Based Practice Use in Skilled Nursing Facilities

PURPOSE This study explored whether perceptions of evidence or organizational context were associated with the use of external memory aids with residents with dementia in skilled nursing facilities (SNFs). METHOD A survey design, supplemented by a small sample of exploratory interviews, was completed within the Promoting Action on Research Implementation in Health Services framework. Ninety-six speech-language pathologists (SLPs) and 68 facility rehabilitation directors (FRDs) completed the Organizational Readiness to Change Assessment (Helfrich, Li, Sharp, & Sales, 2009) in relationship to the use of external memory aids. Five SLPs completed an interview exploring perceptions of evidence and context in relationship to memory aid use. RESULTS SLPs and FRDs had favorable perceptions of evidence supporting memory aids. FRDs perceived the organizational context of the SNF more favorably than SLPs. SLP participants used external memory aids in the past 6 months in 45.89% of cases of residents with dementia. For SLP participants, a 26% (p < .05) increase of external memory aid use was associated with every 1-unit change in favor of the evidence. Interview data revealed barriers to external memory aid implementation. CONCLUSIONS Part of evidence-based practice implementation may be influenced by clinician perceptions. Efforts to increase implementation of external memory aids in SNFs should address these clinician perceptions.

Cognitive and sensory influence on the perception of complex auditory signals

Using positron emission tomography (PET), we have been studying the relationship between psychophysical performance and cortical activation during auditory discrimination tasks. In one experiment, we studied normal hearing listeners who had markedly different perceptual performance on a battery of auditory discrimination tasks. Changes in regional cerebral blood flow (rCBF) were measured while subjects discriminated changes in a tonal sequence or a temporally analogous syllable sequence. The results showed that behavioral performance was correlated with cortical activation in auditory sensory areas as well as cognitive areas related to attention and memory, depending on the demands of the task. To evaluate further whether attention to specific features of complex auditory signals influences the recruitment of cognitive processing areas of the cortex, we studied changes in rCBF when subjects attended to different features of a 1‐octave band signal that varied in spectral envelope frequency (i.e., ripple fr...

Reduced temporal processing in older normal-hearing listeners evident from electrophysiological responses to shifts in interaural time difference

Previous electrophysiological studies of interaural time difference (ITD) processing have demonstrated that ITDs are represented by a nontopographic population rate code. Rather than narrow tuning to ITDs, neural channels have broad tuning to ITDs in either the left or right auditory hemifield, and the relative activity between the channels determines the perceived lateralization of the sound. With advancing age, spatial perception weakens and poor temporal processing contributes to declining spatial acuity. At present, it is unclear whether age-related temporal processing deficits are due to poor inhibitory controls in the auditory system or degraded neural synchrony at the periphery. Cortical processing of spatial cues based on a hemifield code are susceptible to potential age-related physiological changes. We consider two distinct predictions of age-related changes to ITD sensitivity: declines in inhibitory mechanisms would lead to increased excitation and medial shifts to rate-azimuth functions, whereas a general reduction in neural synchrony would lead to reduced excitation and shallower slopes in the rate-azimuth function. The current study tested these possibilities by measuring an evoked response to ITD shifts in a narrow-band noise. Results were more in line with the latter outcome, both from measured latencies and amplitudes of the global field potentials and source-localized waveforms in the left and right auditory cortices. The measured responses for older listeners also tended to have reduced asymmetric distribution of activity in response to ITD shifts, which is consistent with other sensory and cognitive processing models of aging.

A randomized feasibility pilot trial of hearing treatment for reducing cognitive decline: Results from the Aging and Cognitive Health Evaluation in Elders Pilot Study

Hearing loss (HL) is prevalent and independently related to cognitive decline and dementia. There has never been a randomized trial to test if HL treatment could reduce cognitive decline in older adults.

Behavioral and electrophysiological measures of stimulus envelope and fine structure contributions to the binaural masking level difference

The goal of this study is to establish electrophysiological methods for estimating the relative contribution of stimulus envelope and fine-structure cues across a range of clinical populations using a binaural masking level difference (BMLD) paradigm. Stimulus envelope cues were manipulated by the using narrowband noise maskers (50 Hz) with the inherent envelope fluctuations of Gaussian noise (GN) or the reduced envelope fluctuations of low-noise noise (LNN). Fine-structure cues were manipulated by choosing signal frequencies and masker center frequencies of 500 and 4000 Hz. The availability of fine structure cues to the auditory system differs markedly between these two frequencies. Electrophysiological measures consisted of far-field evoked potentials targeting the P1-N1-P2 cortical components. Stimulus maskers were presented continuously at a spectrum level of 60 dB SPL while signal level was varied in descending steps. Threshold was estimated as the lowest signal level that generated a reliable N1-P2 ...

Electrophysiological and behavioral measurements of spectro‐temporal processing: Comodulation masking release

Behavioral experiments using the comodulation masking release (CMR) paradigm indicate that the auditory system is able to encode and compare the temporal characteristics of stimuli across multiple frequency regions. Such processing leads to improved signal detection under certain masking conditions. While there is growing electrophysiological evidence of the coding of temporal patterns at a single spectral region (e.g., the envelope‐following response), few electrophysiological studies have demonstrated (directly or indirectly) across‐frequency processing of temporal patterns. In the present study, behavioral and electrophysiological estimates of signal detection were obtained in masking conditions that typically lead to a CMR. Detection by normal‐hearing human adults was estimated behaviorally using an adaptive staircase technique and electrophysiologically by recording late auditory‐evoked potentials (N1‐P2). Thresholds were estimated for a 1000‐Hz sinusoidal signal (100‐ms duration) in the presence of ...

How Do Age and Hearing Loss Impact Spectral Envelope Perception

Purpose The goal was to evaluate the potential effects of increasing hearing loss and advancing age on spectral envelope perception. Method Spectral modulation detection was measured as a function of spectral modulation frequency from 0.5 to 8.0 cycles/octave. The spectral modulation task involved discrimination of a noise carrier (3 octaves wide from 400 to 3200 Hz) with a flat spectral envelope from a noise having a sinusoidal spectral envelope across a logarithmic audio frequency scale. Spectral modulation transfer functions (SMTFs; modulation threshold vs. modulation frequency) were computed and compared 4 listener groups: young normal hearing, older normal hearing, older with mild hearing loss, and older with moderate hearing loss. Estimates of the internal spectral contrast were obtained by computing excitation patterns. Results SMTFs for young listeners with normal hearing were bandpass with a minimum modulation detection threshold at 2 cycles/octave, and older listeners with normal hearing were remarkably similar to those of the young listeners. SMTFs for older listeners with mild and moderate hearing loss had a low-pass rather than a bandpass shape. Excitation patterns revealed that limited spectral resolution dictated modulation detection thresholds at high but not low spectral modulation frequencies. Even when factoring out (presumed) differences in frequency resolution among groups, the spectral envelope perception was worse for the group with moderate hearing loss than the other 3 groups. Conclusions The spectral envelope perception as measured by spectral modulation detection thresholds is compromised by hearing loss at higher spectral modulation frequencies, consistent with predictions of reduced spectral resolution known to accompany sensorineural hearing loss. Spectral envelope perception is not negatively impacted by advancing age at any spectral modulation frequency between 0.5 and 8.0 cycles/octave.

How aging impacts the encoding of binaural cues and the perception of auditory space

Over the years, the effect of aging on auditory function has been investigated in animal models and humans in an effort to characterize age-related changes in both perception and physiology. Here, we review how aging may impact neural encoding and processing of binaural and spatial cues in human listeners with a focus on recent work by the authors as well as others. Age-related declines in monaural temporal processing, as estimated from measures of gap detection and temporal fine structure discrimination, have been associated with poorer performance on binaural tasks that require precise temporal processing. In lateralization and localization tasks, as well as in the detection of signals in noise, marked age-related changes have been demonstrated in both behavioral and electrophysiological measures and have been attributed to declines in neural synchrony and reduced central inhibition with advancing age. Evidence for such mechanisms, however, are influenced by the task (passive vs. attending) and the stimulus paradigm (e.g., static vs. continuous with dynamic change). That is, cortical auditory evoked potentials (CAEP) measured in response to static interaural time differences (ITDs) are larger in older versus younger listeners, consistent with reduced inhibition, while continuous stimuli with dynamic ITD changes lead to smaller responses in older compared to younger adults, suggestive of poorer neural synchrony. Additionally, the distribution of cortical activity is broader and less asymmetric in older than younger adults, consistent with the hemispheric asymmetry reduction in older adults model of cognitive aging. When older listeners attend to selected target locations in the free field, their CAEP components (N1, P2, P3) are again consistently smaller relative to younger listeners, and the reduced asymmetry in the distribution of cortical activity is maintained. As this research matures, proper neural biomarkers for changes in spatial hearing can provide objective evidence of impairment and targets for remediation. Future research should focus on the development and evaluation of effective approaches for remediating these spatial processing deficits associated with aging and hearing loss.

Distribution of spectral modulation transfer functions in a young, normal-hearing population

Spectral modulation transfer functions (SMTFs) were measured in 49 young (18-35 years of age) normal-hearing listeners. Noise carriers spanned six octaves from 200 to 12 800 Hz. Sinusoidal (on a log-amplitude scale) spectral modulation with random starting phase was superimposed on the carrier at spectral modulation frequencies of 0.25, 0.5, 1.0, 2.0, 4.0, and 8.0 cycles/octave. Modulation detection thresholds (in dB) yielded SMTFs that were bandpass in nature, consistent with previous investigations reporting data for only a few subjects. Thresholds were notably consistent across subjects despite minimal practice. Population statistics are reported that may serve as reference data for future studies.