Classification and cue weighting of multidimensional stimuli with speech-like cues for young normal hearing and elderly hearing-impaired listeners.

OBJECTIVE The purpose of this study was to investigate how young normal-hearing (YNH) and elderly hearing-impaired (EHI) listeners make use of redundant speech-like cues when classifying nonspeech sounds having multiple stimulus dimensions. DESIGN A total of four experiments were conducted with 10 to 12 listeners per group in each experiment. There were 27 stimuli, making use of all possible combinations of three stimulus values along each of three cue dimensions. Stimuli were comprised of two brief sequential noise bursts separated by a temporal gap. Stimulus dimensions were: (1) the center frequency of the noise bursts; (2) the duration of the temporal gap separating the noise bursts; and (3) the direction of a frequency transition in the second noise burst. RESULTS Experiment 1 verified that the stimulus values selected resulted in adjacent steps along each stimulus being easily discriminable [(P(c) > or = 90%]). In experiment 2, similarity judgments were obtained for all possible pairs of the 27 stimuli. Multidimensional scaling confirmed that the three acoustic dimensions existed as separate dimensions perceptually. In experiment 3, listeners were then trained to classify three exemplar stimuli. After the training, they were required to classify all 27 stimuli and these results led to the derivation of attentional weights for each stimulus dimension. Both groups focused their attention on the frequency-transition dimension during the classification task. Finally, experiment 4 demonstrated that the attentional weights derived in experiment 3 were reliable and that both EHI and YNH participants could be trained to shift their attention to a cue dimension (temporal-gap) not preferred in experiment 3, although older adults required much more training to achieve this shift in attention. CONCLUSION For the speech-like, multidimensional acoustic stimuli used here, YNH and EHI listeners attended to the same dimensions of the stimuli when classifying them. In general, the EHI listeners required more time to acquire the ability to categorize the stimuli, and to change their focus to alternate stimulus dimensions.