Andrew Dimitrijevic

Andrew Dimitrijevic
Sunnybrook Health Sciences Centre | sunnybrook · Department of Otolaryngology

PhD

About

49
Publications
10,866
Reads
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3,157
Citations
Introduction
Dr. Dimitrijevic’s lab (http://www.cibrainlab.com) studies the physiology of human hearing in normal hearing and hearing impaired populations. They use electroencephalograms, also known as EEG or “brain waves,” to understand the neural mechanisms of how sound is processed and perceived. A focus of the lab is cochlear implants (CI). The CI is a modern-day medical miracle. It allows people who are deaf to regain hearing by stimulating the auditory nerve and creating neural impulses that reach the brain. People with cochlear implants may hear well in quiet settings but experience difficulties in everyday listening environments, such as following a conversation during a cocktail party. The goal of this research is to understand better the brain mechanisms of hearing with a CI.
Additional affiliations
September 2016 - present
Sunnybrook Health Sciences Centre
Position
  • Managing Director
January 2011 - July 2016
Cincinnati Children's Hospital Medical Center
Position
  • Professor (Assistant)
January 2004 - January 2009
University of California, Irvine
Position
  • PostDoc Position

Publications

Publications (49)
Article
Auditory cortical N100s were examined in ten auditory neuropathy (AN) subjects as objective measures of impaired hearing. Latencies and amplitudes of N100 in AN to increases of frequency (4-50%) or intensity (4-8 dB) of low (250 Hz) or high (4000 Hz) frequency tones were compared with results from normal-hearing controls. The sites of auditory nerv...
Article
Full-text available
Sound modulation is a critical temporal cue for the perception of speech and environmental sounds. To examine auditory cortical responses to sound modulation, we developed an acoustic change stimulus involving amplitude modulation (AM) of ongoing noise. The AM transitions in this stimulus evoked an acoustic change complex (ACC) that was examined pa...
Article
Objective Voice onset time (VOT) is a critical temporal cue for perception of speech in cochlear implant (CI) users. We assessed the cortical auditory evoked potentials (CAEPs) to consonant vowels (CVs) with varying VOTs and related these potentials to various speech perception measures. Methods CAEPs were recorded from 64 scalp electrodes during...
Article
Full-text available
Understanding speech in noise (SiN) is a complex task involving sensory encoding and cognitive resources including working memory and attention. Previous work has shown that brain oscillations, particularly alpha rhythms (8–12 Hz) play important roles in sensory processes involving working memory and attention. However, no previous study has examin...
Article
Full-text available
Listening in a noisy environment is challenging for individuals with normal hearing and can be a significant burden for those with hearing impairment. The extent to which this burden is alleviated by a hearing device is a major, unresolved issue for rehabilitation. Here, we found adult users of cochlear implants (CIs) self-reported listening effort...
Preprint
Full-text available
A common concern in individuals with cochlear implants (CIs) is difficulty following conversations in noisy environments and social settings. The ability to accomplish these listening tasks relies on the individual working memory abilities and draws upon limited cognitive resources to accomplish successful listening. For some individuals, allocatin...
Preprint
Full-text available
There is a weak relationship between clinical and self-reported speech perception outcomes in cochlear implant (CI) listeners. Such poor correspondence may be due to differences in clinical and "real-world" listening environments and stimuli. Speech sounds in the real world are often accompanied by visual cues, background environmental noise and is...
Article
Objective: Evidence suggests that hearing loss increases the risk of cognitive impairment. However, the relationship between hearing loss and cognition can vary considerably across studies, which may be partially explained by demographic and health factors that are not systematically accounted for in statistical models. Design: Middle-aged to ol...
Article
Moderate noise exposure may cause acute loss of cochlear synapses without affecting the cochlear hair cells and hearing threshold; thus, it remains "hidden" to standard clinical tests. This cochlear synaptopathy is one of the main pathologies of noise-induced hearing loss (NIHL). There is no effective treatment for NIHL, mainly because of the lack...
Article
Full-text available
Listening to speech in noise is effortful for individuals with hearing loss, even if they have received a hearing prosthesis such as a hearing aid or cochlear implant (CI). At present, little is known about the neural functions that support listening effort. One form of neural activity that has been suggested to reflect listening effort is the powe...
Article
Full-text available
A common concern for individuals with severe‐to‐profound hearing loss fitted with cochlear implants (CIs) is difficulty following conversations in noisy environments. Recent work has suggested that these difficulties are related to individual differences in brain function, including verbal working memory and the degree of cross‐modal reorganization...
Article
Full-text available
Hearing impairment disrupts processes of selective attention that help listeners attend to one sound source over competing sounds in the environment. Hearing prostheses (hearing aids and cochlear implants, CIs), do not fully remedy these issues. In normal hearing, mechanisms of selective attention arise through the facilitation and suppression of n...
Article
Full-text available
Objectives The ability to understand speech is highly variable in people with cochlear implants (CIs) and to date, there are no objective measures that identify the root of this discrepancy. However, behavioral measures of temporal processing such as the temporal modulation transfer function (TMTF) has previously found to be related to vowel and co...
Article
Objective: To record envelope following responses (EFRs) to monaural amplitude-modulated broadband noise carriers in which amplitude modulation (AM) depth was slowly changed over time and to compare these objective electrophysiological measures to subjective behavioral thresholds in young normal hearing and older subjects. Design: Participants:...
Article
Full-text available
Using noninvasive neuroimaging, researchers have shown that young children have bilateral and diffuse language networks, which become increasingly left-lateralized and focal with development. Connectivity within the distributed pediatric language network has been minimally studied, and conventional neuroimaging approaches do not distinguish task-re...
Article
Recent work has investigated the use of electric stimuli to evoke auditory steady state response (ASSR) in cochlear implant (CI) users. While more control can be exerted using electric stimuli, acoustic stimuli present natural listening environment for CI users. However, ASSR using acoustic stimuli in the presence of a CI could lead to artifacts. F...
Article
Full-text available
Abnormal auditory adaptation is a standard clinical tool for diagnosing auditory nerve disorders due to acoustic neuromas. In the present study we investigated auditory adaptation in auditory neuropathy owing to disordered function of inner hair cell ribbon synapses (temperature-sensitive auditory neuropathy) or auditory nerve fibres. Subjects were...
Article
Objective: Compare brain potentials to consonant vowels (CVs) as a function of both voice onset times (VOTs) and consonant position; initial (CV) versus second (VCV). Methods: Auditory cortical potentials (N100, P200, N200, and a late slow negativity, (SN) were recorded from scalp electrodes in twelve normal hearing subjects to consonant vowels...
Article
Full-text available
Although the cochlear implant (CI) is widely considered the most successful neural prosthesis, it is essentially an open-loop system that requires extensive initial fitting and frequent tuning to maintain a high, but not necessarily optimal, level of performance. Two developments in neuroscience and neuroengineering now make it feasible to design a...
Article
Tinnitus is a phantom sensation of sound in the absence of external stimulation. However, external stimulation, particularly electric stimulation via a cochlear implant, has been shown to suppress tinnitus. Different from traditional methods of delivering speech sounds or high-rate (>2000 Hz) stimulation, the present study found a unique unilateral...
Article
Full-text available
The purpose of this study was to compare cortical brain responses evoked by amplitude modulated acoustic beats of 3 and 6 Hz in tones of 250 and 1000 Hz with those evoked by their binaural beats counterparts in unmodulated tones to indicate whether the cortical processes involved differ. Event-related potentials (ERPs) were recorded to 3- and 6-Hz...
Article
To define brain activity corresponding to an auditory illusion of 3 and 6Hz binaural beats in 250Hz or 1000Hz base frequencies, and compare it to the sound onset response. Event-Related Potentials (ERPs) were recorded in response to unmodulated tones of 250 or 1000Hz to one ear and 3 or 6Hz higher to the other, creating an illusion of amplitude mod...
Article
Full-text available
Steady-state evoked potentials can be recorded from the human scalp in response to auditory stimuli presented at rates between 1 and 200 Hz or by periodic modulations of the amplitude and/or frequency of a continuous tone. Responses can be objectively detected using frequency-based analyses. In waking subjects, the responses are particularly promin...
Article
Auditory temporal processes in quiet are impaired in auditory neuropathy (AN) similar to normal hearing subjects tested in noise. N100 latencies were measured from AN subjects at several tone intensities in quiet and noise for comparison with a group of normal hearing individuals. Subjects were tested with brief 100 ms tones (1.0 kHz, 100-40 dB SPL...
Article
To define cortical brain responses to large and small frequency changes (increase and decrease) of high- and low-frequency tones. Event-Related Potentials (ERPs) were recorded in response to a 10% or a 50% frequency increase from 250 or 4000 Hz tones that were approximately 3 s in duration and presented at 500-ms intervals. Frequency increase was f...
Article
To examine auditory cortical potentials in normal-hearing subjects to intensity increments in a continuous pure tone at low, mid, and high frequency. Electrical scalp potentials were recorded in response to randomly occurring 100 ms intensity increments of continuous 250, 1000, and 4000 Hz tones every 1.4 s. The magnitude of intensity change varied...
Article
We examined auditory cortical potentials in normal hearing subjects to spectral changes in continuous low and high frequency pure tones. Cortical potentials were recorded to increments of frequency from continuous 250 or 4000Hz tones. The magnitude of change was random and varied from 0% to 50% above the base frequency. Potentials consisted of N100...
Article
Full-text available
Event-related potential correlates of the buildup of precedence effect were examined. Buildup is a type of precedence effect illusion in which perception changes (from hearing two clicks to hearing one click) during a click train. Buildup occurs faster for right-leading than left-leading clicks. Continuous click trains that changed leading sides ev...
Article
The relationship between behavioral measures of buildup of precedence effect [or Clifton effect (CE)] and electrophysiological responses using an event‐related potential (ERP) paradigm was examined in 14 young adults with normal hearing. The CE was elicited using a binaural paired‐click (left and right speaker delay) in sound field. This study aime...
Article
Full-text available
Human auditory steady-state responses (ASSRs) were recorded using stimulus rates of 78-95 Hz in normal young subjects, in elderly subjects with relatively normal hearing, and in elderly subjects with sensorineural hearing impairment. Amplitude-intensity functions calculated relative to actual sensory thresholds (sensation level or SL) showed that a...
Article
Full-text available
The number of steady-state responses evoked by the independent amplitude and frequency modulation (IAFM) of tones has been related to the ability to discriminate speech sounds as measured by word recognition scores (WRS). In the present study IAFM stimulus parameters were adjusted to resemble the acoustic properties of everyday speech to see how we...
Article
Full-text available
To compare the magnitudes of the steady-state responses evoked by several types of stimuli, and the times required to recognize these responses as significant. In the first two experiments, we examined auditory steady-state responses to pure tones, broadband noise and band-limited noise. The stimuli were amplitude modulated in the 75 to 100 Hz rang...
Article
Full-text available
This article considers the efficiency of evoked potential audiometry using steady-state responses evoked by multiple simultaneous stimuli with carrier frequencies at 500, 1000, 2000, and 4000 Hz. The general principles of signal-to-noise enhancement through averaging provide a basis for determining the time required to estimate thresholds. The adva...
Article
Full-text available
Steady-state responses are evoked potentials that maintain a stable frequency content over time. In the frequency domain, responses to rapidly presented stimuli show a spectrum with peaks at the rate of stimulation and its harmonics. Auditory steady-state responses can be reliably evoked by tones that have been amplitude-modulated at rates between...
Article
Full-text available
Multiple auditory steady-state responses were evoked by eight tonal stimuli (four per ear), with each stimulus simultaneously modulated in both amplitude and frequency. The modulation frequencies varied from 80 to 95 Hz and the carrier frequencies were 500, 1000, 2000, and 4000 Hz. For air conduction, the differences between physiologic thresholds...
Article
Full-text available
This study examined the steady-state responses evoked by tones modulated with exponential envelopes. The hypothesis was that stimuli with envelopes containing more rapid changes would evoke larger responses. Multiple auditory steady-state responses were recorded simultaneously to eight tonal stimuli, four in each ear. The carrier frequencies of the...
Article
Multiple auditory steady-state responses were evoked by eight tonal stimuli (four per ear), with each stimulus simultaneously modulated in both amplitude and frequency. The modulation frequencies varied from 80 to 95 Hz and the carrier frequencies were 500, 1000, 2000, and 4000 Hz. For air conduction, the differences between physiologic thresholds...
Article
Full-text available
To investigate how phase measurements might facilitate the detection of auditory steady-state responses. Multiple steady-state responses were evoked by auditory stimuli modulated at rates between 78 and 95 Hz and with intensities between 50 and 0 dB SPL. The responses were evaluated in 20 subjects after 1, 2, 4, and 6 min. The responses were analyz...
Article
Independent amplitude and frequency modulation (IAFM) of a carrier tone uses two different modulating frequencies, one for amplitude modulation (AM) and one for frequency modulation (FM). This study measured the human steady-state responses to multiple IAFM tones. The first question was whether the IAFM responses could be recorded without attenuati...
Article
Full-text available
To compare weighted averaging and artifact-rejection to normal averaging in the detection of steady-state responses. Multiple steady-state responses were evoked by auditory stimuli modulated at rates between 78 and 95 Hz. The responses were evaluated after recording periods of 3, 6 and 10 min, using 5 averaging protocols: (1) normal averaging; (2)...
Article
Full-text available
Multiple auditory steady-state responses were recorded using tonal stimuli that were amplitude-modulated (AM), frequency-modulated (FM) or modulated simultaneously in both amplitude and frequency (mixed modulation or MM). When MM stimuli combined 100% AM and 25% FM (12.5% above and below the carrier frequency) and the maximum frequency occurred sim...

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Projects

Projects (2)
Project
To understand the neural processes underlying the ability to selectively listen to auditory targets amongst noise or multitalkers in cochlear implant users
Project
-develop a biomarker of listening effort