[How Sound Modulates Response to Light when Using Various Temporal Intervals between Stimuli of Different Modalities]

Extracellular activity of 34 primary visual cortex neurons of the rabbit was recorded in response to audiovisual stimulation with stimulus onset asynchronies (SOA) in range from -750 to + 150 ms (15 ranges in total). Auditory stimulus: 2000 Hz, 70 dB, 40 ms. Visual stimuli: two weak intensities 0.3 and 1 cd/m2. Sound by itself did not elicit a neuronal response. Factor analysis ANOVA revealed that SOA significantly influence on neuronal responses. Neuronal reaction included responses to increase (on-response) and decrease (off-response) of light intensity. Earliest phase of response (40-100 ms from visual stimuli substitution) is most affected by sound. Neuronal reactions of the every interval of SOA comprised both increase and decrease of discharge in response to addition of a sound. We used a Wilcoxon signed-rank test to show the differences between reactions in response to visual and audio-visual stimuli. Audio-visual on-responses statistically exceeded the responses to visual stimuli at -150, -40 and 0 ms SOA for the all neurons. Two groups of neurons were revealed. The first group (n = 16) showed dependence of on-re- sponses on sound in a wide range of SOA: -150, -40, -20, 0, +20, +50 and +100 ms. Also the first group showed maximum increase of spike number (18-28%) in response to audio-visual stimulation. For the second group of neurons there were no significant SOA for on-responses. We haven't found a significant decrease of audio-visual response compared to a visual response. However, we found the tendency to reduction of audio-visual discharge at intervals SOA -750 and -80 ms (p < 0.07) for the first group and at SOA -500 and +20 ms (p < 0.1) for the second group of neurons. Also we revealed that on-responses are more influenced by sound than off-responses. We have researched the audio-visual interaction in the second phase of neuronal discharges (120-160 ms and later, n = 23). Sound influence on a second phase is weaker than on a first phase. Significant SOA for on-responses: 0 ms; for off-responses: +100 and +150 ms. This study has revealed similarities of audio-visual interaction range for animal and psychophysical researches. Our results allows. to research cross-modal integration in more detail.