Abstract
What governs initial selection of one stimulus over the other in binocular rivalry? A previous study (Mitchell et al, 2004) showed that exogenous attention could determine dominance in binocular rivalry. We replicated their finding with different stimuli, extended the results to endogenous attention and quantified the strength of attention?s effect on dominance. In experiment 1, superimposed +− 45 deg gratings were viewed dioptically for 3 seconds, followed by a brief contrast increment in one of the gratings to direct exogenous attention to that grating. A blank screen was presented for 250 ms (to prevent temporal summation), and then dichoptic stimuli were presented for various durations (100 ∼ 700 ms). Exogenous attention strongly influenced which stimulus was initially dominant in binocular rivalry, consistent with the finding of Mitchell et al (2004). We next measured the strength of exogenous attention by varying the contrast of one of two rival gratings when exogenous attention was previously directed to that grating. The contrast of the attended grating had to be reduced ∼ 50% relative to the unattended grating to counteract attention?s boost to initial dominance. In experiment 2, endogenous attention was manipulated by having participants track one of two oblique gratings both of which independently and continuously changed their orientations and spatial frequencies during a 5 sec period. The rest of the procedure was as same as in experiment 1. The initially dominant grating was most often the one whose orientation matched the grating correctly tracked using endogenous attention. The strengthening effect of endogenous attention on initial dominance was smaller than the effect of exogenous attention. Evidently both exogenous and endogenous attention can influence initial dominance of binocular rivalry, effectively boosting the stimulus strength of the attended rival stimulus.