Effects of visual stimulation on the auditory middle-latency response of the brain

This study compared the click evoked auditory middle-latency response (AMLR) to the click evoked AMLR recorded with competing visual stimuli (a series of blinking red lights). The purpose of the study was to determine if there were any differences in the latencies, amplitudes or morphology of the AMLR wave peaks when the auditory stimulus was presented alone versus when the auditory stimulus was presented with the competing visual stimulus.; AMLRs were recorded from 30 subjects, fifteen males and fifteen females, between the ages of 13 and 30. The acoustic stimuli were one millisecond square wave clicks generated, internally, by a Nicolet Compass Meridian Evoked Potential System and delivered via ER-3A ear inserts. The clicks were presented at a rate of 9.7 per second and at an intensity of 65dB nHL. Each epoch consisted of 1000 click presentations. The AMLR was recorded with silver/silver chloride surface electrodes. A non-inverting electrode was placed at Fz and inverting electrodes were placed at M1 and M2. A nose electrode placement was used as ground. The neuro-electric response to the stimuli was band-passed between 30 and 1500 Hertz, amplified 100,000 times and displayed on a screen with a time window of 100 ms from the stimulus offset.; Results of this study demonstrated that there was an increase in the latencies of the AMLR wave peaks when the visual stimulus was presented as competition to the auditory stimulus. Specifically, there was a statistically significant increase in the amount of time it took to process the AMLR (an increase in the latencies of the wave peaks) when visual competition was present versus when there was no visual stimulus present. The results, however, did not support a significant difference in the amplitudes of the AMLR wave peaks when the visual stimulus was added as competition to the auditory stimulus.; The study findings indicate that there is competition between the senses. Possible implications for the findings are discussed.