Some considerations in evaluating spoken word recognition by normal-hearing, noise-masked normal-hearing, and cochlear implant listeners. I: The effects of response format

Abstract

Objective: The purpose of the present studies was to assess the validity of using closed-set response formats to measure two cognitive processes 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). In addition, the experiments were designed to examine the effects of response format on evaluation of these two abilities in normal-hearing (NH), noise-masked normal-hearing (NMNH), and cochlear implant (CI) subject populations.

Design: The speech recognition performance of NH, NMNH, and CI listeners was measured using both open- and closed-set response formats under a number of experimental conditions. To assess talker normalization abilities, identification scores for words produced by a single talker were compared with recognition performance for items produced by multiple talkers. To examine lexical discrimination, performance for words that are phonetically similar to many other words (hard words) was compared with scores for items with few phonetically similar competitors (easy words).

Results: Open-set word identification for all subjects was significantly poorer when stimuli were produced in lists with multiple talkers compared with conditions in which all of the words were spoken by a single talker. Open-set word recognition also 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 alternatives 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 assessment 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 that NH, NMNH, and CI listeners engage similar perceptual operations to identify 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 discussed.

Figure 1

Comparison of identification scores for words produced by single (dark bars) and multiple (open bars) talkers collapsed across lexical difficulty. The left side of the figure displays data obtained with an open-set response format, and the right side shows results obtained with a closed-set test. The four subject groups are normal-hearing tested in quiet (NH(Q)), normal-hearing tested at +5 (NH(+5)) and −5 (NH(−5)) S/N ratios, and cochlear implant patients (CI). Error bars in this and all subsequent figures indicate standard errors of the mean.

Figure 2

Same as Figure 1 except the data show the effects of lexical difficulty (easy versus hard words) collapsed across single and multiple talkers.

Figure 3

Comparison of open- and closed-set test performance. Group names are the same as in Figure 1.

Figure 4

Effects of talker variability (top) and lexical difficulty (bottom) as measured in a closed-set test designed to maximize confusability between response alternatives and the target item. The group names are the same as in Figure 1.