Motion and binocular rivalry: a window on conscious perception?
01 / 1999 - unknown
In 1999 we have discovered that if you view high-speed motion in one eye and low-speed motion in the other that these incompatible stimuli do not rival. Normally uncorrelated patterns presented to corresponding regions in the two eyes (that is, 'dichoptically') rival strongly, the more so if they are of high contrast, as our moving stimuli were. The low and high speeds are seen transparently rather than in rivalry and we interpret this as supporting evidence for our two-channel proposal (Verstraten et al, 1998). If low speeds are processed in the parvocellular stream through the temporal lobe and high speeds in the magnocellular stream through the parietal lobe, they might reach the neural correlate of consciousness (in the frontal lobe?) separately without interactions. We quantified the ranges of speeds that rival and those that do not and found a good correspondence with the findings in MAE-experiments (Van der Smagt et al., Nature Neurosci. June 1999). If the dynamic MAE represents a gain control of the magno stream, the static MAE of the parvo stream, then their tuning functions (duration versus speed) represent the weighting of speeds in the two channels. From this it is possible to calculate the probability of rivalry/transparency, given a few assumptions about the cooperation of motion detectors. Thus a model can be devised relating the MAE to direct motion vision. This is one goal of the present project and allows us to test various models. The experimental database needs expansion as well. For example, we need to study the dichoptic transparency phenomenon with single step pixel lifetimes (ensuring that only one speed-tuned group of detectors can respond), and we need to look at contrast dependence (since that is different for parvo and magno cells). The psychophysical experiments and modelling efforts will be completed with fMRI-studies to test the hypothesis that the intersection of low-speed and high-speed activity is the neural correlate of consciousness, and to find out where it 'resides' (scattered or concentrated activation patterns?).