EFFECTS OF FORMANT BANDWIDTH ON THE IDENTIFICATION OF SYNTHETIC VOWELS BY COCHLEAR IMPLANT RECIPIENTS

Objective: The main objective was to investigate whether the broadenin g and narrowing of formant bandwidths had a significant effect on the identification of vowels often confused by Nucleus cochlear implant re cipients using the Spectral Peak (SPEAK) speech coding strategy. Speci fically; identification performance for synthetic vowels with the firs t two formants (F1 and F2) parametrically varied in bandwidth was expl ored. Design: Eight implanted subjects identified synthetic versions o f the isolated vowel sounds [I, epsilon, Lambda, boolean OR] with Fl a nd F2 bandwidth manipulations, as well as foil tokens of [i, u, a, ae, 3]. Identification performance was examined in terms of percent corre ct as well as error patterns. Further analyses compared patterns of el ectrode activation. Results: In general, broader F1 bandwidths yielded poorer performance and narrower F1 bandwidths yielded better performa nce relative to identifications for the reference stimuli. However. si milar manipulations of F2 bandwidths resulted in less predictable perf ormance. Comparison of electrode activation patterns indicated a disti nct sharpening or flattening in the F1 frequency region for subjects w ith the greatest performance extremes. Conclusions: Manipulation of F1 bandwidth can result in concomitant changes in electrode activation p atterns and identification performance, This suggests that modificatio ns in the SPEAK coding strategy for the F1 region may be a considerati on. Similar manipulations of F2 bandwidth yielded less predictable res ults and require further investigation.