Repeated Stimulus Exposure Alters the Way Sound Is Encoded in the Human Brain

Auditory training programs are being developed to remediate various types of communication disorders. Biological changes have been shown to coincide with improved perception following auditory training so there is interest in determining if these changes represent biologic markers of auditory learning. Here we examine the role of stimulus exposure and listening tasks, in the absence of training, on the modulation of evoked brain activity. Twenty adults were divided into two groups and exposed to two similar sounding speech syllables during four electrophysiological recording sessions (24 hours, one week, and up to one year later). In between each session, members of one group were asked to identify each stimulus. Both groups showed enhanced neural activity from session-to-session, in the same P2 latency range previously identified as being responsive to auditory training. The enhancement effect was most pronounced over temporal-occipital scalp regions and largest for the group who participated in the identification task. The effects were rapid and long-lasting with enhanced synchronous activity persisting months after the last auditory experience. Physiological changes did not coincide with perceptual changes so results are interpreted to mean stimulus exposure, with and without being paired with an identification task, alters the way sound is processed in the brain. The cumulative effect likely involves auditory memory; however, in the absence of training, the observed physiological changes are insufficient to result in changes in learned behavior

Perceptual and Neurophysiological Effects of Treated and Untreated Hearing Loss in Older Adults

Thesis (Ph.D.)--University of Washington, 2017-03The purpose of this dissertation work was to examine the impact of auditory deprivation in the form of age-related hearing loss (ARHL) and auditory stimulation in the form of hearing aid use, on the neural registration and abilities to use sound for higher level cognitive tasks, in older adults (aged 55-75). Three groups were examined: 1) NH: older adults with clinically normal hearing, 2) u-HL: peers with bilateral mild to moderate/moderately- severe sensory-neural hearing loss who have never worn hearing aids and 3) t-HL: peers with a similar amount of hearing loss, but who have been treated through binaural amplification (hearing aids). Participants completed two sessions: 1) Behavioral tests: Audiometry, cognitive screening, quality of life questionnaires, nonverbal IQ test, speech recognition in quiet and noise, and tests of verbal working memory function (both auditory and visual); 2) Electrophysiology: Evoked potentials (P1-N1-P2) recorded in response to a speech syllable presented at two different sound levels (equal sound pressure level (SPL) and equal sensation level (SL)). All three groups performed similarly on tests of speech perception in noise, working memory and nonverbal IQ, but differed on self-report measures of hearing handicap. Both hearing loss groups indicated greater reported greater hearing handicap (HHIE) than NH groups. Additionally, individuals with untreated hearing loss showed a positive relationship between working memory performance and speech understanding in noise. Neural measures indicated significant morphological differences (latency and amplitude) between groups, but only when the stimuli were presented at equal SPL. Once audibility was accounted for (equal SL levels) these differences were not present, suggesting group differences were due to audibility, and not central changes secondary to auditory deprivation. Results highlight the importance of the audibility of sound, and suggest that early sound processing and later use of sound for processes involved in communication is not permanently affected by mild to moderate/moderately-severe ARHL

CAVET Lipreading

Lipreading task stimul

AV Facemask Task

AV main task stimuli (video recordings, noise, sentence list), and questionnaires

Group averaged P1-N1-P2 complexes recorded from electrode site Cz.

<p>Regardless of stimulus type (“mba” or “ba”), P2 peak amplitudes significantly increased across three sessions for Group 2 (exposure + task) but not Group 1 (exposure only). Sessions 1 and 2 were conducted on two consecutive days. Session 3 was conducted one week later.</p

Electrodes showing the largest and reliable saliencies from MC-PLS in the P2 latency time range.

<p>Note. The average scores are measured for the time points between 190 ms and 290 ms. Listed are the electrodes with the ten largest average saliencies for each stimulus condition.</p>a<p>Absolute value of the average salience * 10⁻²</p>b<p>Absolute value of the average bootstrap ratio</p

Retention Data.

<p>Individual P2 peak amplitude data are shown for all four Sessions in response to the stimulus “mba”. Results shown are from electrode site TP9. When looking at individual subjects, enhanced P2 amplitudes can be seen for many individuals (in Group 2) even though they had not heard these sounds for many months.</p

Results from Mean-Centering PLS analyses.

<p>(A) Electrode Montage. To report PLS results, Electrode locations were classified into 11 sagittal layers indicated by the dotted lines: three lateral (lat1–3), two medial layers (med1–2) in the two hemispheres, and one midline layer (mid). (B) Contrast weights identified for the first significant LV. For each stimulus type, the largest difference was observed between Sessions 1 and 3, in the P2 latency range, for both groups, but the degree of difference was greater in Group 2. (C) Spatiotemporal patterns of electrode saliencies and bootstrap results corresponding to the design LV shown in (B). The x-axis represents time in milliseconds (ms) starting at the stimulus onset marked as 0 ms. The y-axis represents electrodes organized in 11 blocks corresponding to the 11 sagittal layers in the montage shown in (A). Within each block, electrodes are ordered from top to bottom representing anterior to posterior sites. Each horizontal color bar represents temporal patterns of the electrode saliencies for a given electrode. Warm (more red) color illustrates time points with positive differences expressed in the design contrasts; cool (more blue) color expresses those of negative. Positive saliencies (warm color), and negative saliencies (cool color) indicate time points at which the amplitude of the AEP was enhanced over three experimental sessions. Saliencies are scaled with the singular value. For each electrode, horizontal black bars (comprised of individual “x”s) are plotted over the color contrasts to identify the time points at which differences expressed in the contrasts were stable across participants (bootstrap ratios >3).</p

Flowchart describing the procedure.

<p>Flowchart describing the procedure.</p