Abstract
Reaction times (RTs) to crossmodal audiovisual stimuli are typically faster than reaction times to their unimodal components. This enhancement cannot be completely explained by simple statistical facilitation and is often referred to as the ‘redundant signals effect’. It is unknown, however, which aspects of visual processing contribute toward this effect. Here, we considered the separate visual contribution of magnocellular and parvocellular activity; two anatomically and functionally distinct pathways at early processing levels. To attenuate the contribution of magnocellular activity, we presented visual stimuli on a diffuse red background—a condition known to selectively suppress [1] and slow responses to stimuli processed by the magnocellular pathway [2,3]. An isoluminant diffused green background was used for a baseline condition. Stimuli were 40% luminance increment spots with auditory tones, varying in onset relative to visual onset, between -100 (sound first) and 100 (spot first) ms in steps of 20 ms. The results show that when a red background was used, RTs were consistently slower across the range of onset asynchronies. More importantly, we found significantly smaller redundant signals effects for the red background condition. This pattern of results suggests the very fast crossmodal RTs associated with the redundant signals effect are mediated primarily by auditory interaction with magnocellular processes and links crossmodal RT advantage with visual mechanisms that mainly contribute to spatial orientation and action. 1. de Monasterio, F.M. (1978). Properties of concentrically organized X and Y ganglion cells of macaque retina. Journal of Neurophysiology, 41, 1394–1417. 2. West G.L., Bedwell J., Anderson A.K., Pratt J. (2010) Red diffuse light suppresses the accelerated perception of fear. Psychological Science, 21, 992–999. 3. Breitmeyer, B.G., & Breier, J.I. (1994). Effects of background color on reaction time to stimuli varying in size and contrast: Inferences about human M channels. Vision Research, 34, 1039–1045.
Meeting abstract presented at VSS 2015