Sumitrajit Dhar - Academia.edu (original) (raw)

Papers by Sumitrajit Dhar

Purpose: To explore the contribution of cardiovascular disease (CVD) risk factors on hearing outc... more Purpose: To explore the contribution of cardiovascular disease (CVD) risk factors on hearing outcomes. Background: A staggering 31 million Americans have hearing loss, a figure quickly growing as the population ages. Age-related hearing loss manifests bilaterally at high frequencies and may result in social isolation, anxiety, and depression. CVD risk factors contribute substantially to morbidity and mortality yet there are no data to clarify the long-term association between CVD risk status and hearing outcomes. In this pilot study, we explore the effects of low-risk (LR) and not LR status on hearing in older adults. Methods: Participants were classified as LR or not LR for CVD in young adulthood (25-55 years). Thirty-nine years later, a subset of 130 CHAS participants (18.7% black, 28.5% female) aged 65-84 years underwent advanced audiologic assessment including hearing thresholds (0.25-8.0 kHz) and distortion product otoacoustic emission (DPOAE; 0.50-5.0 kHz) testing. Results: We...

Introduction: There is evidence that hearing impairment (HI) is associated with depression in eth... more Introduction: There is evidence that hearing impairment (HI) is associated with depression in ethnically diverse groups. The objective of this study was to determine if Hispanics with HI and reduced hearing-related quality of life (QOL) have more depressive symptoms than Hispanics without HI. Methods: We examined HI and depression in Hispanic adults aged 18+ (N=16,415) from the HCHS/SOL. Pure Tone Average (PTA; based on thresholds at 0.5,1,2,4 kHz) for the better ear was computed from audiometric data, with higher scores indicating greater HI. Hearing-related QOL was measured by the Hearing Handicap Inventory for the Elderly (HHIE) and the Hearing Handicap Inventory for Adults (HHIA), and depression was measured by the Center for Epidemiologic Studies Depression Scale-10. Generalized linear models stratified by gender, with adjustments for covariates (age, Hispanic background, income, cigarette use, doctor's visit in the past 12 months) and survey design, were performed using th...

American Journal of Audiology

To investigate masking release for speech maskers for linguistically and phonetically close (Engl... more To investigate masking release for speech maskers for linguistically and phonetically close (English and Dutch) and distant (English and Mandarin) language pairs. Thirty-two monolingual speakers of English with normal audiometric thresholds participated in the study. Data are reported for an English sentence recognition task in English and for Dutch and Mandarin competing speech maskers (Experiment 1) and noise maskers (Experiment 2) that were matched either to the long-term average speech spectra or to the temporal modulations of the speech maskers from Experiment 1. Listener performance increased as the target-to-masker linguistic distance increased (English-in-English < English-in-Dutch < English-in-Mandarin). Spectral differences between maskers can account for some, but not all, of the variation in performance between maskers; however, temporal differences did not seem to play a significant role.

The Journal of the Acoustical Society of America, 2015

Working memory capacity has been linked to performance on many higher cognitive tasks, including ... more Working memory capacity has been linked to performance on many higher cognitive tasks, including the ability to perceive speech in noise. Current efforts to train working memory have demonstrated that working memory performance can be improved, suggesting that working memory training may lead to improved speech perception in noise. A further advantage of working memory training to improve speech perception in noise is that working memory training materials are often simple, such as letters or digits, making them easily translatable across languages. The current effort tested the hypothesis that working memory training would be associated with improved speech perception in noise and that materials would easily translate across languages. Native Mandarin Chinese and native English speakers completed ten days of reversed digit span training. Reading span and speech perception in noise both significantly improved following training, whereas untrained controls showed no gains. These data suggest that working memory training may be used to improve listeners' speech perception in noise and that the materials may be quickly adapted to a wide variety of listeners.

JAMA otolaryngology-- head & neck surgery, Jan 28, 2015

Hearing impairment is common in adults, but few studies have addressed it in the US Hispanic/Lati... more Hearing impairment is common in adults, but few studies have addressed it in the US Hispanic/Latino population. To determine the prevalence of hearing impairment among US Hispanic/Latino adults of diverse backgrounds and determine associations with potential risk factors. The Hispanic Community Health Study/Study of Latinos (HCHS/SOL) is a population-based sample of Hispanics/Latinos in four US communities (Bronx, New York; Chicago, Illinois; Miami, Florida; and San Diego, California). Examinations were conducted from 2008 through 2011. The HCHS/SOL examined 16 415 self-identified Hispanic/Latino persons aged 18 to 74 years recruited from randomly selected households using a stratified 2-stage area probability sample design based on census block groups and households within block groups. Hearing thresholds were measured by pure-tone audiometry. Hearing impairment was defined as a pure-tone average (PTA) of thresholds at 0.5, 1, 2, and 4 kHz greater than 25 dB hearing level. Bilatera...

AIP conference proceedings, 2011

Invariant distortion product otoacoustic emission (DPOAE) phase elucidates scaling symmetry in th... more Invariant distortion product otoacoustic emission (DPOAE) phase elucidates scaling symmetry in the cochlea. Below some low-frequency boundary, DPOAE phase slope steepens. The origin of this break in phase invariance is not clear. Stimulus frequency (SF)OAE delays computed from the slope of phase also manifest discontinuities at low frequencies, though the relationship between the breaking of cochlear scaling as defined by SFOAE and DPOAE metrics has not been examined. In this study, OAEs were recorded in normal-hearing human adults to probe cochlear scaling and its breaking and to examine the correspondence between two OAE metrics of scaling. Results indicate: (1) the apical break in DPOAE phase invariance cannot be explained by contributions from the reflection-source component; (2) DPOAE phase signals a break from scaling near 1.5 kHz and (3) DPOAE and SFOAE metrics of cochlear scaling produce phase discontinuities within approximately one-quarter octave of each other and show com...

Page 1. Plural Publishing Newsletter Spring 2010 Otoacoustic Emissions (OAEs): A 30-Year Perspect... more Page 1. Plural Publishing Newsletter Spring 2010 Otoacoustic Emissions (OAEs): A 30-Year Perspective James W. Hall III, Ph.D. University of Florida Sumitrajit Dhar, Ph.D. Northwestern University The First Decade: Discovery of OAEs and Outer Hair Cell Motility ...

The Journal of the Acoustical Society of America, 2014

The reliability of nine measures of the stimulus level in the human ear canal was compared by mea... more The reliability of nine measures of the stimulus level in the human ear canal was compared by measuring the sensitivity of behavioral hearing thresholds to changes in the depth of insertion of an otoacoustic emission probe. Four measures were the ear-canal pressure, the eardrum pressure estimated from it and the pressure measured in an ear simulator with and without compensation for insertion depth. The remaining five quantities were derived from the ear-canal pressure and the Thévenin-equivalent source characteristics of the probe: Forward pressure, initial forward pressure, the pressure transmitted into the middle ear, eardrum sound pressure estimated by summing the magnitudes of the forward and reverse pressure (integrated pressure) and absorbed power. Two sets of behavioral thresholds were measured in 26 subjects from 0.125 to 20 kHz, with the probe inserted at relatively deep and shallow positions in the ear canal. The greatest dependence on insertion depth was for transmitted pressure and absorbed power. The measures with the least dependence on insertion depth throughout the frequency range (best performance) included the depth-compensated simulator, eardrum, forward, and integrated pressures. Among these, forward pressure is advantageous because it quantifies stimulus phase.

International Journal of Pediatric Otorhinolaryngology, 2007

Biophysics of the Cochlea, 2003

The recent work of Talmadge et al. [1] and Shera and Guinan [2] argues for two distinct mechanism... more The recent work of Talmadge et al. [1] and Shera and Guinan [2] argues for two distinct mechanisms for the production of otoacoustic emissions: i) a retrograde traveling wave produced by the amplifier induced pressure gradient across the basilar membrane due primarily to the nonlinearities inherent in the amplifier, and ii) linear coherent reflections encompassing intracochlear standing waves. It would

Neuropsychologia, 2009

Spoken language processing in noisy environments, a hallmark of the human brain, is subject to ag... more Spoken language processing in noisy environments, a hallmark of the human brain, is subject to agerelated decline, even when peripheral hearing might be intact. The present study examines the cortical cerebral hemodynamics (measured by fMRI) associated with such processing in the aging brain. Younger and older subjects identified single words in quiet and in two multi-talker babble noise conditions (SNR 20 and −5 dB). Behaviorally, older and younger subjects did not show significant differences in the first two conditions but older adults performed less accurately in the SNR -5 condition. The fMRI results showed reduced activation in the auditory cortex but an increase in working memory and attention-related cortical areas (prefrontal and precuneus regions) in older subjects, especially in the SNR -5 condition. Increased cortical activities in general cognitive regions were positively correlated with behavioral performance in older listeners, suggestive of a compensatory strategy. Furthermore, inter-regional correlation revealed that while younger subjects showed a more streamlined cortical network of auditory regions in response to spoken word processing in noise, older subjects showed a more diffused network involving frontal and ventral brain regions. These results are consistent with the decline-compensation hypothesis, suggestive of its applicability to the auditory domain.

Neurology, 2013

The NIH Toolbox project has assembled measurement tools to assess a wide range of human perceptio... more The NIH Toolbox project has assembled measurement tools to assess a wide range of human perception and ability across the lifespan. As part of this initiative, a small but comprehensive battery of auditory tests has been assembled. The main tool of this battery, pure-tone thresholds, measures the ability of people to hear at specific frequencies. Pure-tone thresholds have long been considered the "gold standard" of auditory testing, and are normally obtained in a clinical setting by highly trained audiologists. For the purposes of the Toolbox project, an automated procedure (NIH Toolbox Threshold Hearing Test) was developed that allows nonspecialists to administer the test reliably. Three supplemental auditory tests are also included in the Toolbox auditory test battery: assessment of middle-ear function (tympanometry), speech perception in noise (the NIH Toolbox Words-in-Noise Test), and self-assessment of hearing impairment (the NIH Toolbox Hearing Handicap Inventory Ages 18-64 and the NIH Toolbox Hearing Handicap Inventory Ages 64+). Tympanometry can help differentiate conductive from sensorineural pathology. The NIH Toolbox Words-in-Noise Test measures a listener's ability to perceive words in noisy situations. This ability is not necessarily predicted by a person's pure-tone thresholds; some people with normal hearing have difficulty extracting meaning from speech sounds heard in a noisy context. The NIH Toolbox Hearing Handicap Inventory focuses on how a person's perceived hearing status affects daily life. The test was constructed to include emotional and social/situational subscales, with specific questions about how hearing impairment may affect one's emotional state or limit participation in specific activities. The 4 auditory tests included in the Toolbox auditory test battery cover a range of auditory abilities and provide a snapshot of a participant's auditory capacity.

Journal of the American Academy of Audiology, 2008

Individuals with impaired hearing find it difficult to understand speech in the presence of backg... more Individuals with impaired hearing find it difficult to understand speech in the presence of background noise--a problem addressed effectively by directional microphones. As open-canal fittings have become increasingly popular in the recent past, so has the debate about the effective directional benefit available from these devices. This study investigates the benefit of directional microphones in two commercially available open-canal behind-the-ear hearing aids using the Hearing in Noise Test (HINT). Sixteen individuals, between 50 and 85 year of age, with high-frequency bilateral sensorineural hearing loss and no previous hearing aid experience participated in this study. Data Collection and Analysis: Individuals were asked to repeat sentences (presented at 0 degrees azimuth) in the presence of a diffuse-field uncorrelated broadband speech-shaped noise. HINT performance was compared across hearing instruments and conditions using a linear model with repeated measures. There was a directional advantage of 2.6 dB as compared to the unaided condition. Average performance was worse in the omnidirectional mode as compared to the unaided condition. These results suggest that directional signal processing should not be precluded in open-canal instruments for listening in noisy environments.

Journal of the American Academy of Audiology, 2006

Distortion product otoacoustic emissions (DPOAEs) recorded in the ear canal are a composite or ve... more Distortion product otoacoustic emissions (DPOAEs) recorded in the ear canal are a composite or vector sum of two underlying components. The relationship between hearing thresholds and DPOAE-component level, rather than composite level, has been of recent interest. Two different signal-processing methods, inverse fast Fourier transform (IFFT) with time-windowing and low-pass filtering, were used to obtain estimates of the levels of the two components. Component estimates were then correlated to behavioral thresholds. Improvement in the strength of the correlation was not significant over that of the composite. While the signal processing methods were found to yield similar estimates of the generation component, application of the IFFT with time-windowing method was more complex due to the overlap of the components in the time domain. This time domain variability was observed both within and between subjects. These results highlight the complexities of DPOAE generation and the related difficulties of component separation.