A signal detection analysis of the effects of hearing on the visual recognition of two-digit numbers

A signal detection measure of visual recognition was used to assess the visual recognition of two-digit numbers in three different conditions: (1) voicing of the number as it was presented visually; (2) voicing of a different number than the one presented; and (3) no voicing. The three treatment means were significantly different, with matched voicing resulting in the best performance and no voicing, in the worst. There was no evidence that the treatments differentially affected response cri teria. Smith (1965) reported that visual recognition was facilitated by a perceptual interaction with hearing. In his study, each 0 was required to recognize a tachistoscopically presented list of 25 two-digit numbers. Each visual presentation was accompanied by a voicing by the E. There were 5 matched trials during which E voiced the same number that was presented visually. On the 20 mismatched trials, E voiced a number other than the one presented visually. The voicing began prior to and terminated after the visual stimulus. The visual exposure duration used for each 0 was the median estimate of the thresholds for three numbers as obtained by the method of limits. The Os were instructed to respond only when they were at least 50% sure of being correct. It was found that Os had significantly better visual recognition in the matched condition than they had in the mismatched condition. This outcome has important implications for theories dealing with the way humans process information si m ultaneously presented in two sensory modalities. However, there was a possible artifact in Smith's procedure. In order to correct for the possible tendency of each 0 to try to achieve more hits in the matched trials by simply repeating the number that he heard E voice, Smith adjusted the number of correct trials obtained in the matched condition with the proportion of times that 0 responded on the mismatched trials with the same number that had just been voiced. If that proportion were 25%, for example, then the total number correct in the matched condition was reduced by 25%. This approach to response bias is based on the traditional high-threshold model of the sensory system and no longer appears valid in the light of a great deal of recent research by signal detection theorists (Green & Swets, 1966; Swets, 1964). The signal detection model considers O's errors to be based on valid sensory information and not the result of guessing. Regardless of O's sensitivity, the obtained error rate can be high or low, depending on the value of being correct and the cost of being wrong. Loveless, Brebner, and Hamilton (1970), in their review of bisensory stimulation research, have criticized studies such as Smith's from a signal detection viewpoint. Simultaneous stimulation in a second modality can raise O's hit rate not only through sensory interaction, but by changing O's decision criterion so that he becomes more likely to respond that a signal was present during the observation interval. The purpose of this experiment, therefore, was to assess Smith's (1965) results, using a signal detection analysis of the recognition task. In addition to the matched and mismatched conditions, a no-voicing condition was included in order to determine if mismatching actually inhibits visual recognition.