Doctor of Philosophy

dissertationAmplitude modulation (AM) detection measures a listener's sensitivity to temporal envelope fluctuations. AM signals are ecologically relevant because the amplitude of speech fluctuates over time. The post-cochlear representation of AM may be influenced by processes that occur in the cochlea, where signals are subject to cochlear compression and adaptive mechanisms that modulate the cochlear response such as the medial olivocochlear (MOC) reflex. Specifically, cochlear compression may reduce the difference between high-intensity peaks and low-intensity valleys (i.e., effective modulation depth) of AM. Furthermore, gain reduction of the cochlear amplifier via the MOC reflex is hypothesized to decompress the cochlear input-output function and thus improve the AM effective modulation depth at moderate levels. To test these hypotheses, AM detection was measured for a narrow-band, high-frequency carrier (5000 Hz) for conditions that do or do not elicit the MOC reflex. These conditions take advantage of the sluggish onset of the reflex, which exhibits an onset delay (?25 ms) upon stimulation. Specifically, AM detection was measured as a function of level for a 50 ms carrier in the presence and absence of a long ipsilateral notched-noise precursor. A longer carrier (500 ms) without a precursor was also included. For no-precursor condition, AM detection thresholds at moderate carrier levels are poorer compared to low and high levels, consistent with a reduced effective modulation depth due to cochlear compression. In the precursor condition, AM thresholds improved monotonically with carrier level, with the largest improvements seen at moderate levels. This improvement is consistent with decompression of the cochlear input-output function via the MOC reflex. For 500 ms carriers, AM detection thresholds improved by a constant (across all carrier levels) relative to AM thresholds with a precursor, consistent with the longer carrier providing more "looks" to detect the AM signal. In a second experiment, AM thresholds were measured as a function of modulation frequency to examine whether the effects of the precursor depend on the modulation frequency. The results showed that the improvement in AM detection with compared to without a precursor is limited to low modulation frequencies (<60Hz). The experiment in Chapter 3 was designed to examine the effects of cochlear compression on the inherent fluctuations of narrow-band noise carriers. To test this, AM detection was measured for short and long, high- and low-fluctuating noise carriers as a function of carrier level. The results showed that AM thresholds for short, low-fluctuating noise carriers worsened as carrier level increased from low to mid carrier levels and then improved with further increases in carrier level, as found in the previous experiment. This is consistent with greater cochlear compression at moderate levels. For high-fluctuating carriers, AM thresholds were roughly constant across carrier levels. For high-fluctuating carriers, low-level linear and mid-level compressive cochlear response growth may have resulted in constant envelope signal-to-noise ratios, due to the cochlear response growth equally affecting the target modulation and inherent carrier fluctuations. Thus, AM detection for high-fluctuating carriers is constant as a function of carrier level

Using Spiritual Connections to Cope With Stress and Anxiety During the COVID-19 Pandemic

During the initial phases of the COVID-19 pandemic, stress and anxiety were pervasive among the masses due to high morbidity and mortality. Besides the fear of coronavirus was also particularly driven by social media. Many people started to look for faith and spiritual connections to gain comfort. The role of spiritual ties and religious beliefs in relation to coping with pandemic stress has acquired the attention of researchers in some parts of the world. This cross-sectional survey aimed at assessing the intensity of stress and anxiety symptoms experienced by people and how much they were alleviated by employing spiritual connections. The study sample comprises 795 respondents with 52% males and 48% females living in Saudi Arabia. The brief online study questionnaire collected data about background variables, anxiety and stress scale from DASS-21, and items from the WHOQOL (SRBP) instrument assessed the use of spiritual beliefs to cope. Multiple regression models were tested to determine the role of spiritual connections after adjusting demographic variables. Results illustrated that after adjusting for gender and age, participants’ anxiety symptoms decreased by (β = −0.27; p = 0.000) units with each unit increase in the use of spiritual connections, and participants’ stress symptoms reduce by (β = −0.36; p = 0.000) units with each unit increase in coping with spirituality. Additionally, females’ risk to experience anxiety and stress symptoms was more than males [(β = 0.88; p = 0.01) and (β = 0.92; p = 0.000)], respectively. An increase in age decreases the likelihood of experiencing anxiety symptoms and stress symptoms by (β = −0.75; p = 0.02) and (β = −0.11; p = 0.000) units, respectively. Findings support the protective role of spiritual connections despite small beta coefficients. The social and cultural context in Saudi Arabia favors deep-rooted connections with spirituality and faith. Our findings support the fact that the reliance on spiritual connections helped older people to deal with exaggerated fear during the initial phase of the COVID-19 pandemic and reduces the risk of experiencing anxiety and stress symptoms. Females and younger participants were relatively vulnerable to developing these symptoms. We discussed these findings considering some recent studies that reported similar relationships and made recommendations for future research

Natural killer cells attenuate cytomegalovirus-induced hearing loss in mice

<div><p>Congenital cytomegalovirus (CMV) infection is the most common non-hereditary cause of sensorineural hearing loss (SNHL) yet the mechanisms of hearing loss remain obscure. Natural Killer (NK) cells play a critical role in regulating murine CMV infection via NK cell recognition of the Ly49H cell surface receptor of the viral-encoded m157 ligand expressed at the infected cell surface. This Ly49H NK receptor/m157 ligand interaction has been found to mediate host resistance to CMV in the spleen, and lung, but is much less effective in the liver, so it is not known if this interaction is important in the context of SNHL. Using a murine model for CMV-induced labyrinthitis, we have demonstrated that the Ly49H/m157 interaction mediates host resistance in the temporal bone. BALB/c mice, which lack functional Ly49H, inoculated with mCMV at post-natal day 3 developed profound hearing loss and significant outer hair cell loss by 28 days of life. In contrast, C57BL/6 mice, competent for the Ly49H/m157 interaction, had minimal hearing loss and attenuated outer hair cell loss with the same mCMV dose. Administration of Ly49H blocking antibody or inoculation with a mCMV viral strain deleted for the m157 gene rendered the previously resistant C57BL/6 mouse strain susceptible to hearing loss to a similar extent as the BALB/c mouse strain indicating a direct role of the Ly49H/m157 interaction in mCMV-dependent hearing loss. Additionally, NK cell recruitment to sites of infection was evident in the temporal bone of inoculated susceptible mouse strains. These results demonstrate participation of NK cells in protection from CMV-induced labyrinthitis and SNHL in mice.</p></div

Survey respondents’ knowledge and awareness of various medical conditions.

Survey respondents’ knowledge and awareness of various medical conditions.</p

Dataset and summary data for women who had heard of cytomegalovirus.

(XLSX)</p

Knowledge of CMV modes of transmission among survey respondents that previously heard of CMV.

Knowledge of CMV modes of transmission among survey respondents that previously heard of CMV.</p

Knowledge of symptoms of congenital CMV among survey respondents that previously heard of CMV.

Knowledge of symptoms of congenital CMV among survey respondents that previously heard of CMV.</p

Comparative Study of Audiovestibular Symptoms between Early and Late Variants of COVID-19

Audiovestibular symptoms during the acute phase of the corona virus disease 2019 (COVID-19), have been reported for earlier waves of the pandemic, while no studies investigated nor compared audiovestibular manifestations during subsequent waves of COVID-19. In the current study, we aimed to compare the occurrence of audiovestibular symptoms associated with COVID-19 between the alpha/beta, delta, and omicron variants. An online questionnaire was distributed to individuals with confirmed test results for COVID-19. We asked participants to report whether they experienced audiovestibular symptoms during the acute phase of the disease. The study included 939 participants; 120 un-infected controls and infected participants during alpha/beta (n = 301), delta (n = 102), and omicron (n = 416) predominance periods. Self-reported audiovestibular symptoms were found to be statistically significantly different between un-infected controls and COVID-19 infected individuals in all analyzed variants. Furthermore, our results showed no significant differences in audiovestibular symptoms among individuals infected during alpha/beta, delta, and omicron waves. Although individuals infected during the delta variant predominance period reported higher percentages of audiovestibular symptoms (ranging from 11.8% to 26.5% for auditory symptoms and from 12.7% to 34.3% for vestibular symptoms) than for the alpha/beta (ranging from 6.3% to 18.9% for auditory symptoms and 8.3% to 29.9% for vestibular symptoms) and omicron (ranging from 9.6% to 21.2% for auditory and 12.5 to 29.1% for vestibular symptoms) variants, this did not achieve statistical significance. With regards to auditory symptoms, the most commonly reported symptoms were aural fullness followed by hearing loss and tinnitus. With regards to vestibular symptoms, dizziness was the most commonly reported symptom followed by vertigo and unsteadiness. Logistic regression revealed that experiencing auditory symptoms were associated with other neurological symptoms, back and joint pain, and chest pain as COVID-19 symptoms. Vestibular symptoms were associated with anemia, gender, fatigue, headache, and breathing difficulties. In conclusion, our study shows that audiovestibular symptoms are common during the acute phase of early and late COVID-19 variants with no significant differences between them

Knowledge of preventative measures against CMV among survey respondents that previously heard of CMV.

Knowledge of preventative measures against CMV among survey respondents that previously heard of CMV.</p

Dataset and summary data for all study participants.

(XLSX)</p