Fig. 2.

Network responses to two types of rivalry stimuli. Red represents neural responses to vertical gratings, and blue represents responses to horizontal gratings. (A) Traditional rivalry stimuli consist of orthogonal gratings presented continuously to the two eyes. In response, the left and right monocular neurons first briefly respond together for ≈150 msec (arrow) and then settle into an alternation in which one gains dominance and suppresses the other via inhibition. The dominant neuron then undergoes slow spike-rate adaptation until the opposite monocular neurons are released from inhibition, and the cycle repeats. This competitive alternation is reflected in responses at the higher binocular level, which is driven by its oscillatory monocular inputs. (B) A novel rivalry stimulus incorporates 18.0-Hz on-off flicker of the orthogonal gratings coupled with swapping the stimuli between eyes every 333 msec (6). In response, the monocular neurons no longer generate a competitive response alternation; instead, both vertical and horizontal neural responses are always simultaneously present (double-headed arrow). This provides equivalent input to the higher-level binocular neurons, which now generate a rivalry alternation caused by their own competitive inhibitory interactions. The result is perceptual rivalry (with superimposed flicker) with a dominance duration almost equal to that with traditional rivalry stimuli. As illustrated by the heavy horizontal bar, perceptual rivalry generated by the model extends over six to seven monocular stimulus reversals, thus demonstrating that rivalry cannot be caused by monocular competition in this instance. All results are in complete agreement with human psychophysical data (6).