Multiple looks in speech sound discrimination in adults

N. F. Viemeister and G. H. Wakefield's (1991) multiple looks hypothesis is a theoretical approach from the psychoacoustic literature that has promise for bridging the gap between results from speech perception research and results from psychoacoustic research. This hypothesis accounts for sensory detection data and predicts that if the "looks" at a stimulus are independent and information is combined optimally, sensitivity should increase for 2 pulses relative to 1 pulse. Specifically, d' (a bias-free measure of sensitivity) for 2 pulses should be larger than d' for 1 pulse. One speech discrimination paradigm that presents stimuli with multiple presentations is the change/no-change procedure. On a change trial, the standard and comparison stimuli differ; on a no-change trial, they are the same. Normal-hearing adults were tested using the change/no-change procedure with 3 consonant-vowel minimal pairs in combinations of 1, 2, and 4 repetitions of standard and comparison stimuli at various signal-to-noise ratios. If multiple looks extend to this procedure, performance should increase with higher repetition numbers. Performance increased with more presentations of the speech contrasts tested. The multiple looks hypothesis predicted performance better at low repetition numbers when performance was near d' values of 1.0 than at higher repetition numbers and higher performance levels.