SOME CONSIDERATIONS IN EVALUATING SPOKEN WORD RECOGNITION BY NORMAL-HEARING, NOISE-MASKED NORMAL-HEARING, AND COCHLEAR IMPLANT LISTENERS .1. THE EFFECTS OF RESPONSE FORMAT

Objective: The purpose of the present studies was to assess the validi ty of using closed-set response formats to measure two cognitive proce sses essential for recognizing spoken words-perceptual normalization ( the ability to accommodate acoustic-phonetic variability) and lexical discrimination (the ability to isolate words in the mental lexicon). I n addition, the experiments were designed to examine the effects of re sponse format on evaluation of these two abilities in normal-hearing ( NH), noise-masked normal-hearing (NMNH), and cochlear implant (CI) sub ject populations. Design: The speech recognition performance of NH, NM NH, and CI listeners was measured using both open- and closed-set resp onse formats under a number of experimental conditions. To assess talk er normalization abilities, identification scores for words produced b y a single talker were compared with recognition performance for items produced by multiple talkers. To examine lexical discrimination, perf ormance for words that are phonetically similar to many other words (h ard words) was compared with scores for items with few phonetically si milar competitors (easy words). Results: Open-set word identification for all subjects was significantly poorer when stimuli were produced i n lists with multiple talkers compared with conditions in which all of the words were spoken by a single talker. Open-set word recognition a lso was better for lexically easy compared with lexically hard words. Closed-set tests, in contrast, failed to reveal the effects of either talker variability or lexical difficulty even when the response altern atives provided were systematically selected to maximize confusability with target items. Conclusions: These findings suggest that, although closed-set tests may provide important information for clinical asses sment of speech perception, they may not adequately evaluate a number of cognitive processes that are necessary for recognizing spoken words . The parallel results obtained across all subject groups indicate tha t NH, NMNH, and CI listeners engage similar perceptual operations to i dentify spoken words. Implications of these findings for the design of new test batteries that can provide comprehensive evaluations of the individual capacities needed for processing spoken language are discus sed.