All are welcome to attend the following PhD oral defense. The defense will be held in the Graduate Student Centre, Room 200, at 12:30pm, next Monday, September 9th.
Exam Time: 12:30 PM on Monday, September 9, 2024 (Please arrive 5 minutes early, so the exam can begin promptly).
Exam Location: Room 200 of the Graduate Student Centre (6371 Crescent Road).
FREQUENCY AND COCHLEAR PLACE SPECIFICITY OF NARROWBAND CHIRPS FOR AUDITORY BRAINSTEM RESPONSE AUDIOMETRY
By Ronald Nkansah Adjekum
Committee: David Stapells (Co-Supervisor) and Navid Shahnaz (Co-Supervisor)
Abstract
Many studies have demonstrated that 2-1-2 (cycles) tones and other brief tones with similar duration are reasonably frequency specific and are preferred over shorter tonal stimuli for threshold estimation using the auditory brainstem response (ABR). In recent years, some researchers have recommended using a newer stimulus, narrowband chirps (NBchirps), for threshold estimation instead of the more standard 2-1-2 cycles stimuli. This is mainly because NBchirps often result in larger ABR wave V amplitudes. Some researchers have raised concerns regarding the possibility that the increased amplitudes observed with NBchirp, compared to the more standard tonal stimuli, could be due to the potentially poorer frequency specificity of NBchirps. Additionally, the acoustic spectra of NBchirps appear to be visually broader than those of the more standard 2-1-2 stimuli (although a detailed spectral analysis of these stimuli has not been studied), and it remains unclear whether ABRs elicited by these stimuli demonstrate poorer cochlear place specificity compared to more standard 2-1-2 tones. This dissertation carried-out two studies. Study 1 investigated the frequency specificity of NBchirps by comparing the spectral characteristics of NBchirps with those of the standard 2-1-2 tones. Study 2 assessed the cochlear place specificity of the ABR to NBchirp versus 2-1-2 stimuli using the high-pass noise derived response technique. The results of Study 1 showed that the main lobe bandwidth of the NBchirp acoustic spectra was 1.4-1.9 times wider than those for the 2-1-2 tones. Study 2 found that the ABRs to both NBchirp and 2-1-2 stimuli were reasonably place specific. However, Study 2 also showed that the ABR to NBchirps received additional contributions from frequency places 0.5 to 1 octave higher than those observed for the 2-1-2 stimuli. In conclusion, the ABR to NBchirp stimuli reflects wider cochlear regions than the ABR to 2-1-2 stimuli, an increase which may be problematic when assessing some hearing losses. The often-larger responses to NBchirps might simply be explained by the stimulation of wider cochlear regions, rather than (or in addition to) the basilar-membrane-optimized timing of NBchirps. Further studies are needed to compare ABR thresholds to NBchirps versus standard tonal stimuli in individuals with steeply sloping (or rising) sensorineural hearing loss.