Asunto(s)

RESUMEN

A sudden increase in the amplitude of a component often causes its segregation from a complex tone, and shorter rise times enhance this effect. We explored whether this also occurs in implant listeners (n = 8). Condition 1 used a 3.5-s "complex tone" comprising concurrent stimulation on five electrodes distributed across the array of the Nucleus CI24 implant. For each listener, the baseline stimulus level on each electrode was set at 50% of the dynamic range (DR). Two 1-s increments of 12.5%, 25%, or 50% DR were introduced in succession on adjacent electrodes within the "inner" three of those activated. Both increments had rise and fall times of 30 and 970 ms or vice versa. Listeners reported which increment was higher in pitch. Some listeners performed above chance for all increment sizes, but only for 50% increments did all listeners perform above chance. No significant effect of rise time was found. Condition 2 replaced amplitude increments with decrements. Only three listeners performed above chance even for 50% decrements. One exceptional listener performed well for 50% decrements with fall and rise times of 970 and 30 ms but around chance for fall and rise times of 30 and 970 ms, indicating successful discrimination based on a sudden rise back to baseline stimulation. Overall, the results suggest that implant listeners can use amplitude changes against a constant background to pick out components from a complex, but generally these must be large compared with those required in normal hearing. For increments, performance depended mainly on above-baseline stimulation of the target electrodes, not rise time. With one exception, performance for decrements was typically very poor.

Asunto(s)

RESUMEN

The evidence that cochlear implant listeners routinely experience stream segregation is limited and equivocal. Streaming in these listeners was explored using tone sequences matched to the center frequencies of the implant's 22 electrodes. Experiment 1 measured temporal discrimination for short (ABA triplet) and longer (12 AB cycles) sequences (tone/silence durations = 60/40 ms). Tone A stimulated electrode 11; tone B stimulated one of 14 electrodes. On each trial, one sequence remained isochronous, and tone B was delayed in the other; listeners had to identify the anisochronous interval. The delay was introduced in the second half of the longer sequences. Prior build-up of streaming should cause thresholds to rise more steeply with increasing electrode separation, but no interaction with sequence length was found. Experiment 2 required listeners to identify which of two target sequences was present when interleaved with distractors (tone/silence durations = 120/80 ms). Accuracy was high for isolated targets, but most listeners performed near chance when loudness-matched distractors were added, even when remote from the target. Only a substantial reduction in distractor level improved performance, and this effect did not interact with target-distractor separation. These results indicate that implantees often do not achieve stream segregation, even in relatively unchallenging tasks.

Asunto(s)

RESUMEN

Previous claims that auditory stream segregation occurs in cochlear implant listeners are based on limited evidence. In experiment 1, eight listeners heard tones presented in a 30-s repeating ABA-sequence, with frequencies matching the centre frequencies of the implant's 22 electrodes. Tone A always stimulated electrode 11 (centre of the array); tone B stimulated one of the others. Tone repetition times (TRTs) from 50 to 200 ms were used. Listeners reported when they heard one or two streams. The proportion of time that each sequence was reported as segregated was consistently greater with increased electrode separation. However, TRT had no significant effect, and the perceptual reversals typical of normal-hearing listeners rarely occurred. The results may reflect channel discrimination rather than stream segregation. In experiment 2, six listeners performed a pitch-ranking task using tone pairs (reference=electrode 11). Listeners reported which tone was higher in pitch (or brighter in timbre) and their confidence in the pitch judgement. Similarities were observed in the individual pattern of results for reported segregation and pitch discrimination. Many implant listeners may show little or no sign of automatic stream segregation owing to the reduced perceptual space within which sounds can differ from one another.

Asunto(s)

RESUMEN

The Birmingham bone-anchored hearing aid (BAHA) programme has fitted more than 300 patients with unilateral bone-anchored hearing aids since 1988. Some of the patients who benefited well with unilateral aids and who had used bilateral conventional aids previously applied for bilateral amplification. To date, 15 patients have been fitted with bilateral BAHAs. The benefits of bilateral amplification have been compared to unilateral amplification in 11 of these patients. Subjective analysis in the form of validated comprehensive questionnaires was undertaken. The Glasgow benefit inventory (GBI), which is a subjective patient orientated post-interventional questionnaire developed to evaluate any otorhinolaryngological surgery and therapy was administered. The results revealed that the use of bilateral bone-anchored hearing aids significantly enhanced general well being (patient benefit) and improved the patient's state of health (quality of life). The Chung and Stephens questionnaire which addresses specific issues related to binaural hearing was used. Our preliminary results are encouraging and are comparable to the experience of the Nijmegen BAHA group.

Asunto(s)

RESUMEN

The Birmingham bone-anchored hearing aid (BAHA) programme, since its inception in 1988, has fitted more than 300 patients with unilateral bone-anchored hearing aids. Recently, some of the patients who benefited extremely well with unilateral aids applied for bilateral amplification. To date, 15 patients have been fitted with bilateral BAHAs. The benefits of bilateral amplification have been compared to unilateral amplification in 11 of these patients who have used their second BAHA for 12 months or longer. Following a subjective analysis in the form of comprehensive questionnaires, objective testing was undertaken to assess specific issues such as 'speech recognition in quiet', 'speech recognition in noise' and a modified 'speech-in-simulated-party-noise' (Plomp) test. 'Speech in quiet' testing revealed a 100 per cent score with both unilateral and bilateral BAHAs. With 'speech in noise' all 11 patients scored marginally better with bilateral aids compared to best unilateral responses. The modified Plomp test demonstrated that bilateral BAHAs provided maximum flexibility when the origin of noise cannot be controlled as in day-to-day situations. In this small case series the results are positive and are comparable to the experience of the Nijmegen BAHA group.

Asunto(s)