Auditory-Tactile integration: Effects of Phase of Sinusoidal Stimulation at 50 and 250 Hz

The perceptual integration of 50- and 250-Hz, 500-ms vibrotactile and auditory tones was studied in detection experiments as a function of the relative phase (0°, 72°, 144°, 216°, and 288°) of the tone pulses. Vibrotactile stimuli were delivered through a single-channel vibrator to the left middle fingertip and auditory stimuli were presented diotically through headphones in a background of 50 dB SPL broadband noise. The observers were four adults with normal hearing. The vibrotactile and auditory stimulus levels used each yielded 63-77%-Correct unimodal detection performance in a two-interval two-alternative forced-choice task. Scores for the auditory-alone and tactile-alone conditions averaged roughly 70%-Correct. Mean scores for the auditory plus tactile conditions averaged across different phases were 77.1%-Correct at 50 Hz and 79.6%-Correct at 250 Hz. At 50 Hz, no differences in performance were observed as a function of the relative phase at which the combined auditory and tactile signals were presented. At 250 Hz, significantly higher scores were observed for one phase combination (72°) compared to two of the other four relative phases. Performance on the auditory plus tactile conditions resulted in significant integrative effects and was generally more consistent with a "Pythagorean Sum" model than with either an "Algebraic Sum" or an "Optimum Single Cannel" model of perceptual integration.