Identification of multidimensional stimuli containing speech cues and the effects of training

The purpose of this study was to determine how listeners with normal hearing make use of cues from multiple, independent stimulus dimensions when classifying synthesized stimuli containing acoustic cues found in speech. Listeners classified synthesized stimuli that differed on three independent and discriminable dimensions. The three dimensions of the stimuli included: (1) the fricative spectrum center frequency; (2) the slope of the frequency transition; and (3) the duration of the temporal gap. Each of the three dimensions could take on one of three possible values. Twenty-seven stimuli were synthesized using all possible combinations of the values on the three dimensions. Multidimensional scaling of paired-comparison similarity judgments confirmed the existence of three perceptual dimensions. Listeners were then trained to classify three exemplar stimuli as "circle," "triangle," and "square," respectively. Following this training, subjects classified all 27 stimuli as "circle," "triangle," and "square." From this it was determined how each listener's attention was distributed among the dimensions. Results indicated the listeners did not pay equal attention to the three stimulus dimensions. In addition, it was demonstrated that it was possible to train a listener to attend to a dimension that was not previously used to classify the stimuli.