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Open Access Publications from the University of California

Scholarly Works (20 results)

  • Article
  • Peer Reviewed
UC Irvine Previously Published Works (2020)
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.
    Cover page: Tinnitus Does Not Interfere with Auditory and Speech Perception
    • Thesis
    • Peer Reviewed
    UC Irvine Electronic Theses and Dissertations (2018)

    Tinnitus is the phantom perception of sound without an external acoustic source. Although tinnitus affects 10-15% of adults, with symptoms from mildly bothersome to debilitating, current treatments are limited by an inadequate understanding of its underlying pathophysiology. Improved understanding must address perception at all levels, from a peripheral deficit (e.g. hearing loss), to central auditory plasticity generating the internal signal, to higher-order brain networks governing its conscious awareness. The first study examined top-down mechanisms of attention in modulating tinnitus and potentially its loudness, pitch, or distress. Subjects with and without chronic tinnitus monitored one of two tonal steams, one with similar frequency as tinnitus and the other well-outside this region. Cortical evoked-potentials showed enhanced attentional gain when tinnitus subjects focused to the tinnitus frequency, which related to increased tinnitus loudness. A later enhancement to the non-tinnitus frequency suggested tinnitus also impacts selective processing of other sounds. A discrimination analysis indicated that attention-derived variables could serve as a biomarker to detect tinnitus from control subjects with similar age and hearing. The second study employed psychophysical methods to uncover sensory deficits in tinnitus and improve its diagnosis. Tinnitus subjects showed normal temporal acuity for detecting silent gaps in pure-tones, including those matching the tinnitus pitch. Although gap detection is widely used to assess tinnitus in animal research, assuming tinnitus “fills-in” the gap, the procedure appears ill-suited for clinical diagnosis in humans. Tinnitus subjects also showed normal frequency discrimination. However, slightly improved intensity discrimination of low-level sounds indicated a mechanism of increased auditory gain in the central pathways. Together, these results suggest that “bottom-up” sensory deficits in tinnitus have subtle impacts on basic auditory processing, while top-down attention plays a central role in gating tinnitus perception and may be developed as an objective clinical biomarker.

      Cover page: Perceptual Consequences of Tinnitus: Effects of Sensory Deficits and Top-Down Attention
      • Article
      Journal of Citrus Pathology, Volume 1, Issue 1 (2014)

      The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, has spread to citrus growing regions nearly worldwide and transmits phloem-limited bacteria (Candidatus Liberibacter spp.) that are putatively responsible for citrus greening disease.  Host plant resistance may hold promise as a control tactic for ACP, but ACP has a broad host range and resistance in Citrus and relatives to ACP has only recently been actively explored.  Very low abundances of ACP were found on two accessions of Poncirus trifoliata L. in a field survey (Westbrook et al., 2011).  Therefore, we tested whether 81 accessions of P. trifoliata and xCitroncirus sp. (hybrids of P. trifoliata and Citrus spp.) from the USDA-ARS National Clonal Germplasm Repository for Citrus and Dates were resistant to ACP by determining whether these accessions influence oviposition and lifespan of adults in no-choice tests.  There was a higher abundance of eggs on the control (Citrus macrophylla Wester) than nearly all accessions of P. trifoliata, and zero eggs were laid on 36% of the accessions.  Additionally, more eggs were laid on the control than 10 of 34 accessions of xCitroncirus.  Lifespan of adults was ~2.5-5 times longer on 11 of the 17 trifoliates and trifoliate hybrids we tested.  P. trifoliata appears to have both antixenosis and antibiosis resistance to ACP.  We have initiated research to identify the specific traits conferring resistance.  To identify chemical mechanisms that may promote resistance, we collected volatiles from several pairs of closely related susceptible/resistant accessions of trifoliates and trifoliate hybrids and found differences in the volatile profiles.

        Cover page: Resistance of Poncirus and Citrus x Poncirus Germplasm to the Asian Citrus PsyllidCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        Fisher Center Working Papers (1995)
          Cover page: Pricing Mortgage-Backed Securities in a Multifactor Interest Rate Environment: A Multivariate Density Estimation Approach
          • Article
          • Peer Reviewed
          Fisher Center Working Papers (2004)
            Cover page: Valuing Mutual Fund Companies
            • Article
            • Peer Reviewed
            UC Irvine Previously Published Works (2024)
            Attention plays an important role in not only the awareness and perception of tinnitus but also its interactions with external sounds. Recent evidence suggests that attention is heightened in the tinnitus brain, likely as a result of relatively local cortical changes specific to deafferentation sites or global changes that help maintain normal cognitive capabilities in individuals with hearing loss. However, most electrophysiological studies have used passive listening paradigms to probe the tinnitus brain and produced mixed results in terms of finding a distinctive biomarker for tinnitus. Here, we designed a selective attention task, in which human adults attended to one of two interleaved tonal (500 Hz and 5 kHz) sequences. In total, 16 tinnitus (5 females) and 13 age- and hearing-matched control (8 females) subjects participated in the study, with the tinnitus subjects matching the tinnitus pitch to 5.4 kHz (range = 1.9-10.8 kHz). Cortical responses were recorded in both passive and attentive listening conditions, producing no differences in P1, N1, and P2 between the tinnitus and control subjects under any conditions. However, a different pattern of results emerged when the difference was examined between the attended and unattended responses. This attention-modulated cortical response was significantly greater in the tinnitus than control subjects: 3.9-times greater for N1 at 5 kHz (95% CI: 2.9 to 5.0, p = 0.007, ηp2 = 0.24) and 3.0 for P2 at 500 Hz (95% CI: 1.9 to 4.5, p = 0.026, ηp2 = 0.17). We interpreted the greater N1 modulation as local neural changes specific to the tinnitus frequency and the greater P2 as global changes to hearing loss. These two cortical measures were used to differentiate between the tinnitus and control subjects, producing 83.3% sensitivity and 76.9% specificity (AUC = 0.81, p = 0.006). These results suggest that the tinnitus brain is more plastic than that of the matched non-tinnitus controls and that the attention-modulated cortical response can be developed as a clinically meaningful biomarker for tinnitus.
              Cover page: Attention-Modulated Cortical Responses as a Biomarker for Tinnitus †
              • Article
              Fisher Center Working Papers (2004)

              Combining insights from the contingent claims and the asset-backed securities literatures, we study the economics of value creation in the asset management business. In particular, we provide a theoretical model and a closed form formula for the value of fund fees in the presence of the well known flow-performance relation, giving rise to interesting nonlinearities and volatility-related effects. The theoretical model sheds light on the role of fees, asset growth, asset and benchmark volatility, and the intensity of the flow-performance relation. To better understand the role of changing fund characteristics such as age and size on the fund value and fund risk, we estimate the empirical relation between returns and flows conditional on these characteristics for various asset classes. We study these effects using Monte Carlo simulations for various economically meaningful parameter values for specific asset classes. Measuring value as a fraction of assets under management, we find that both value and risk, systematic and idiosyncratic, decline in size and age. In addition, value is a complex, non-monotonic function of the fee charged on the fund.

                Cover page: Valuing Mutual Fund Companies
                • Article
                • Peer Reviewed
                UC Irvine Previously Published Works (2021)

                Objectives

                Electric stimulation is used to treat a number of neurologic disorders such as epilepsy and depression. However, delivering the required current to far-field neural targets is often ineffective because of current spread through low-impedance pathways. Here, the specific aims are to develop an empirical measure for current passing through the human head and to optimize stimulation strategies for targeting deeper structures, including the auditory nerve, by utilizing the cochlear implant (CI).

                Materials and methods

                Outward input/output (I/O) functions were obtained by CI stimulation and recording scalp potentials in five CI subjects. Conversely, inward I/O functions were obtained by noninvasive transcranial electric stimulation (tES) and recording intracochlear potentials using the onboard recording capability of the CI.

                Results

                I/O measures indicate substantial current spread, with a maximum of 2.2% gain recorded at the inner ear target during tES (mastoid-to-mastoid electrode configuration). Similarly, CI stimulation produced a maximum of 1.1% gain at the scalp electrode nearest the CI return electrode. Gain varied with electrode montage according to a point source model that accounted for distances between the stimulating and recording electrodes. Within the same electrode montages, current gain patterns varied across subjects suggesting the importance of tissue properties, geometry, and electrode positioning.

                Conclusion

                These results provide a novel objective measure of electric stimulation in the human head, which can help to optimize stimulation parameters that improve neural excitation of deep structures by reducing the influence of current spread.

                Conflict of interest

                The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
                  Cover page: Input–Output Functions in Human Heads Obtained With Cochlear Implant and Transcranial Electric Stimulation
                  • Article
                  • Peer Reviewed
                  UC Irvine Previously Published Works (2022)
                  Cochlear implant (CI) users show limited sensitivity to the temporal pitch conveyed by electric stimulation, contributing to impaired perception of music and of speech in noise. Neurophysiological studies in cats suggest that this limitation is due, in part, to poor transmission of the temporal fine structure (TFS) by the brainstem pathways that are activated by electrical cochlear stimulation. It remains unknown, however, how that neural limit might influence perception in the same animal model. For that reason, we developed non-invasive psychophysical and electrophysiological measures of temporal (i.e., non-spectral) pitch processing in the cat. Normal-hearing (NH) cats were presented with acoustic pulse trains consisting of band-limited harmonic complexes that simulated CI stimulation of the basal cochlea while removing cochlear place-of-excitation cues. In the psychophysical procedure, trained cats detected changes from a base pulse rate to a higher pulse rate. In the scalp-recording procedure, the cortical-evoked acoustic change complex (ACC) and brainstem-generated frequency following response (FFR) were recorded simultaneously in sedated cats for pulse trains that alternated between the base and higher rates. The range of perceptual sensitivity to temporal pitch broadly resembled that of humans but was shifted to somewhat higher rates. The ACC largely paralleled these perceptual patterns, validating its use as an objective measure of temporal pitch sensitivity. The phase-locked FFR, in contrast, showed strong brainstem encoding for all tested pulse rates. These measures demonstrate the cat's perceptual sensitivity to pitch in the absence of cochlear-place cues and may be valuable for evaluating neural mechanisms of temporal pitch perception in the feline animal model of stimulation by a CI or novel auditory prostheses.
                    Cover page: Temporal Pitch Sensitivity in an Animal Model: Psychophysics and Scalp Recordings
                    • Article
                    • Peer Reviewed
                    UC Irvine Previously Published Works (2024)

                    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.
                      Cover page: Exploring the Use of Interleaved Stimuli to Measure Cochlear-Implant Excitation Patterns.
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