2. Some results of a binocular rivalry/fMRI experiment on the 1.5 T magnet at Gainesville. The correlations shown are with a reference wave that peaks 4 sec after the "switch". Later experiments suggest that the haemodynamic response is still increasing as long as 8 sec after the "switch". Of course, studying such "late" responses is a problem in the average subject who switches every second or so! Hence the great reliance placed in these experiments on "slow switchers" whose perception may reverse at intervals as long as 10 seconds if the contrast of the stimulus is low.