Animal studies have discovered that noise, even at levels that produce no permanent threshold shift, may cause cochlear damage and selective nerve degeneration. A hallmark of such damage, or synaptopathy, is recovered threshold but reduced suprathreshold amplitude for the auditory brainstem response (ABR) wave I. The objective of the present study is to evaluate whether the ABR wave I amplitude or slope can be used to diagnose tinnitus in humans. A total of 43 human subjects, consisting of 21 with tinnitus and 22 without tinnitus, participated in the study. The subjects were on average 44 ± 24 (standard deviation) years old and 16 were female; a subgroup of 19 were young adults with normal audiograms from 125 to 8000 Hz. The ABR was measured using ear canal recording tiptrodes for clicks, 1000, 4000 and 8000 Hz tone bursts at 30, 50, and 70 dB nHL. Compared with control subjects, tinnitus subjects did not show reduced ABR wave I amplitude or slope in either the entire group of 21 tinnitus subjects or a subset of tinnitus subjects with normal audiograms. Despite the small sample size and diverse tinnitus population, the present result suggests that low signal-to-noise ratios in non-invasive measurement of the ABR limit its clinical utility in diagnosing tinnitus in humans.
Abstract Rationale Electrophysiological studies show that nicotine enhances neural responses to characteristic frequency stimuli. Previous behavioral studies partially corroborate these findings in young adults, showing that nicotine selectively enhances auditory processing in difficult listening conditions. The present work extended previous work to include both young and older adults and assessed the nicotine effect on sound frequency and intensity discrimination. Objectives Hypotheses were that nicotine improves auditory performance and that the degree of improvement is inversely proportional to baseline performance. Methods Young (19–23 years old) normal-hearing nonsmokers and elderly (61–80) nonsmokers with normal hearing up to at least 2 kHz received nicotine gum (6 mg) or placebo gum in a single-blind, randomized crossover design. Participants performed three experiments (frequency discrimination, frequency modulation identification, and intensity discrimination) before and after treatment. The perceptual differences were analyzed between post-treatment nicotine and placebo conditions as a function of pre-treatment baseline performance. Results Nicotine significantly improved performance for intensity discrimination, and improvement was more pronounced in the elderly with lower baseline performance. Nicotine had no overall effect on the two frequency related tasks. Conclusions Nicotine effects are task-dependent, enhancing intensity discrimination but not frequency performance.
Tinnitus is a sound heard by 15% of the general population in the absence of any external sound. Because external sounds can sometimes mask tinnitus, tinnitus is assumed to affect the perception of external sounds, leading to hypotheses such as "tinnitus filling in the temporal gap" in animal models and "tinnitus inducing hearing difficulty" in human subjects. Here we compared performance in temporal, spectral, intensive, masking and speech-in-noise perception tasks between 45 human listeners with chronic tinnitus (18 females and 27 males with a range of ages and degrees of hearing loss) and 27 young, normal-hearing listeners without tinnitus (11 females and 16 males). After controlling for age, hearing loss, and stimulus variables, we discovered that, contradictory to the widely held assumption, tinnitus does not interfere with the perception of external sounds in 32 of the 36 measures. We interpret the present result to reflect a bottom-up pathway for the external sound and a separate top-down pathway for tinnitus. We propose that these two perceptual pathways can be independently modulated by attention, which leads to the asymmetrical interaction between external and internal sounds, and several other puzzling tinnitus phenomena such as discrepancy in loudness between tinnitus rating and matching. The present results suggest not only a need for new theories involving attention and central noise in animal tinnitus models but also a shift in focus from treating tinnitus to managing its comorbid conditions when addressing complaints about hearing difficulty in individuals with tinnitus. SIGNIFICANCE STATEMENT Tinnitus, or ringing in the ears, is a neurologic disorder that affects 15% of the general population. Here we discovered an asymmetrical relationship between tinnitus and external sounds: although external sounds have been widely used to cover up tinnitus, tinnitus does not impair, and sometimes even improves, the perception of external sounds. This counterintuitive discovery contradicts the general belief held by scientists, clinicians, and even individuals with tinnitus themselves, who often report hearing difficulty, especially in noise. We attribute the counterintuitive discovery to two independent pathways: the bottom-up perception of external sounds and the top-down perception of tinnitus. Clinically, the present work suggests a shift in focus from treating tinnitus itself to treating its comorbid conditions and secondary effects.
Attempts to use current-focusing strategies in cochlear-implant (CI) stimulation to reduce neural spread-of-excitation have met with only mixed success in human CI studies, in contrast to promising results in animal studies. Although this discrepancy could stem from between-species anatomical and aetiological differences, it may be that the masking experiments used in human studies are insufficiently sensitive to differences in excitation-pattern width. We used an interleaved-masking method to measure psychophysical excitation patterns in seven participants with four masker stimulation configurations: monopolar (MP), partial tripolar (pTP), a wider partial tripolar (pTP+2), and, importantly, a condition (RP+2) designed to produce a broader excitation pattern than MP. The probe was always in partial-tripolar configuration. We found a significant effect of stimulation configuration on both the amount of on-site masking (mask and probe on same electrode; an indirect indicator of sharpness) and the difference between off-site and on-site masking. Differences were driven solely by RP+2 producing a broader excitation pattern than the other configurations, whereas monopolar and the two current-focusing configurations did not statistically differ from each other. Hence a method that is sensitive enough to reveal a modest broadening in RP+2 showed no evidence for sharpening with focussed stimulation. We also showed that although voltage recordings from the implant accurately predicted a broadening of the psychophysical excitation patterns with RP+2, they wrongly predicted a strong sharpening with pTP+2. We additionally argue, based on our recent research, that the interleaved-masking method can usefully be applied to non-human species and objective measures of CI excitation patterns.
Research Article| April 01 2008 Teaching Students about Biodiversity by Studying the Correlation between Plants & Arthropods Matthew L. Richardson, Matthew L. Richardson Search for other works by this author on: This Site PubMed Google Scholar Janice Hari Janice Hari Search for other works by this author on: This Site PubMed Google Scholar The American Biology Teacher (2008) 70 (4): 217–220. https://doi.org/10.2307/30163247 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Matthew L. Richardson, Janice Hari; Teaching Students about Biodiversity by Studying the Correlation between Plants & Arthropods. The American Biology Teacher 1 April 2008; 70 (4): 217–220. doi: https://doi.org/10.2307/30163247 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentThe American Biology Teacher Search This content is only available via PDF. Copyright National Association of Biology Teachers Article PDF first page preview Close Modal You do not currently have access to this content.
Cold exposure can result in core body temperature reductions and subsequent physiological and psychological effects. While the physiological effects of core temperature cooling have been well documented, a precise method of quantification of cognitive performance during cold stress is yet to be established. We investigated the effects of a 1oC drop in rectal temperature in male subjects at two different exposure temperatures (5oC and 12oC circulated water in a liquid-cooled garment) on the P300 event-related potential waveform during a dual modality (auditory and visual) continuous performance task. Changes in waveform amplitude and latency suggested modification of task engagement or perceived difficulty, and speed of processing, respectively. Decreases in amplitude occurred in both 5oC and 12oC conditions, and increases in latency occurred in the 5oC condition compared to control subjects. It was suggested that cognitive performance suffered in terms of task engagement as rectal temperature decreased, with speed of processing slowed in the 5oC condition. The further use of event-related potential recordings in future thermal studies is discussed.
Abstract Purpose Attempts to use current-focussing strategies with cochlear implants (CI) to reduce neural spread-of-excitation have met with only mixed success in human studies, in contrast to promising results in animal studies. Although this discrepancy could stem from between-species anatomical and aetiological differences, the masking experiments used in human studies may be insufficiently sensitive to differences in excitation-pattern width. Methods We used an interleaved-masking method to measure psychophysical excitation patterns in seven participants with four masker stimulation configurations: monopolar (MP), partial tripolar (pTP), a wider partial tripolar (pTP + 2), and, importantly, a condition (RP + 2) designed to produce a broader excitation pattern than MP. The probe was always in partial-tripolar configuration. Results We found a significant effect of stimulation configuration on both the amount of on-site masking (mask and probe on same electrode; an indirect indicator of sharpness) and the difference between off-site and on-site masking. Differences were driven solely by RP + 2 producing a broader excitation pattern than the other configurations, whereas monopolar and the two current-focussing configurations did not statistically differ from each other. Conclusion A method that is sensitive enough to reveal a modest broadening in RP + 2 showed no evidence for sharpening with focussed stimulation. We also showed that although voltage recordings from the implant accurately predicted a broadening of the psychophysical excitation patterns with RP + 2, they wrongly predicted a strong sharpening with pTP + 2. We additionally argue, based on our recent research, that the interleaved-masking method can usefully be applied to non-human species and objective measures of CI excitation patterns.
Sound spectra are represented by patterns of activity along the tonotopic axis ofthe cochlea. Cochlear implants can transmit spectra by stimulating tonotopicallyappropriate electrodes, but fidelity is limited by intracochlear spread of excitation. We aim to better evaluate present-day experimental stimulation procedures and, potentially, to improve transmission of spectra with novel stimulation modalities. As a first step, we are developing non-invasive measures of tonotopic spread of excitation that can be compared between normal-hearing cats and humans. These measures include psychophysics in the present study and scalp-recorded electrophysiology in a companion study (Guérit et al., 2021). Cats and humans detected pure-tone probes presented in continuous 1/8- and 1-oct noise-band maskers. Masker bandwidths were readily discernable in both species by the dependence of masked thresholds on probe frequencies. Thresholds were largely constant across the bandwidth of the 1-oct masker, whereas thresholds dropped markedly at frequencies away from the center of the 1/8-oct masker. Cats and humans differed in that the feline auditory filter centered on 8 kHz, which we measured using a notched-noise procedure, was 22% wider than published values for humans at the same center frequency. Also, thresholds for the cats in the 1-octmasker condition consistently were 1.0 to 3.2 dB higher than expected based on the estimated masker power in the feline auditory filter. The present psychophysical results parallel those in our companion electrophysiological study, thereby providing perceptual validation for that study. These psychophysical and electrophysiological methods will be valuable for future investigations of novel approaches for auditory prosthesis.
