Studies of implantee speech reception are undertaken to understand the limitations of present cochlear prostheses in order to develop improved devices and procedures. Intensive multifactorial studies on a group of about 40 highly committed implantees are planned. The three sub-projects reflect different approaches to the problem of evaluating and improving cochlear implants. Basic Psychophysics is directed at determining the cues used in forming fundamental auditory percepts and developing new psychophysical measures to predict speech-reception ability. Cochlear implants can elicit patterns of neural activity (and percepts) that cannot be produced with acoustic stimulation. Predictive measures of speech reception provide substantial insight into fundamental mechanisms that limit device effectiveness. Promising predictive measures based on absolute thresholds and simultaneous electrode interactions will be extended to new measures of nonsimultaneous interactions and temporal activity. Quantitative Analysis of Cue Integration in Speech Reception is directed at assessing perceptual integration of cues in closed-set speech identification tasks. This research exploits a new analytical framework that quantifies how performance in a """"""""combined"""""""" mode (e.g., audiovisual stimulation) is influenced by integration or interference of cues available in the isolated """"""""component"""""""" modes (e.g, audio and visual stimulation alone). In addition to audiovisual integration, implantees' abilities to integrate cues from multiple electrodes will be analyzed. Speech Processing is directed at investigating fundamental aspects of sound encoding for electroauditory stimulation and developing processing schemes that improve implant performance. This work exploits the direct access to the intracochlear electrode array afforded by the Ineraid implant, thereby permitting arbitrary changes in the processing to be easily applied. Research will focus on a promising family of multichannel processors incorporating nonsimultaneous pulsatile stimulation of channel electrodes coupled with high information content delivered to each channel. The rationale for this processing is to minimize electric field interactions that have been shown to be significant in psychophysical tests. These studies will make use of a new real-time, laboratory-based, digital speech- processing system and wearable processors that may become available from Richards Medical Co.
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