Stream segregation on a single electrode as a function of pulse rate in cochlear implant listeners.
Date
2010
Author
Advisors
Collins, Leslie M
Cartee, Lianne
Nolte, Loren W.
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Abstract
While cochlear implants usually provide a high level of speech recognition in quiet,
speech recognition in noise and music appreciation remain challenging. In response
to these issues, several studies have proposed increasing the number of channels of
information through multiple pulse rate strategies. For the selection of pulse rates,
studies of multi-rate strategies have considered implementation issues such as harmonics,
pitch saturation, and tonotopic order but have not considered the fundamental perceptual
question of whether two pulse rates can provide independent channels of information
on a single electrode. This study measures stream segregation as an indicator of whether
different pulse rates on the same electrode can be perceived independently. This approach
differs from that of previous stream segregation studies which focused on stimulation
of alternating electrodes, with the motivation of determining a relationship between
electrode stream segregation and speech perception in challenging noisy environments.
Stream segregation in this study was measured using two stimulus sequences following
an A-B-A-B structure where A and B were different pulse rates stimulatingthe same
electrode. The timing between A and B was controlled to provide either aregular or
irregular gap between the two pulse trains. The threshold at which subjects could
distinguish a regular rhythm from an irregular rhythm was used as an estimate of stream
segregation since detecting an irregular rhythm is an easier task when the streams
are fused. Stream segregation in cochlear implant users, as with normal hearing listeners,
was hypothesized to be influenced by factors such as frequency and the relative timing
between tones. To attempt to assess the relationship between these and stream segregation,
subjects’ rate discrimination and gap detection abilities were also measured. The
results of this study indicate that stream segregation can occur for two pulse rates
on a single electrode; thus, it may be possible to use pulse rates to create additional
channels of information. Further, the stream segregation results were not strongly
correlated with the gap detection or rate discrimination results. The lack of correlation
with the gap detection results suggests that the task was measuring a separate perceptual
phenomenon rather than providing another measure of gap detection. The lack of correlation
with the rate discrimination results suggests that discriminability may not be a limiting
factor in selecting rates for segregation. These results may have implications for
the future design of multi-rate speech processing strategies.
Type
Master's thesisDepartment
Electrical and Computer EngineeringSubject
Acoustic StimulationAdult
Aged
Audiometry
Auditory Threshold
Cochlear Implantation
Cochlear Implants
Correction of Hearing Impairment
Cues
Female
Humans
Male
Middle Aged
Noise
Perceptual Masking
Periodicity
Persons With Hearing Impairments
Prosthesis Design
Psychoacoustics
Recognition (Psychology)
Signal Processing, Computer-Assisted
Speech Perception
Time Factors
Time Perception
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https://hdl.handle.net/10161/3152Citation
Duran, Sara I. (2010). Stream segregation on a single electrode as a function of pulse rate in cochlear implant
listeners. Master's thesis, Duke University. Retrieved from https://hdl.handle.net/10161/3152.Collections
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