In rivalry, constant stimuli allow several interpretations ("percepts"). Percepts are characterized by their probability to occur and by the duration of their dominance. During continuous presentation of bi-stable stimuli, both percept probabilities are trivially 50%. To disentangle the processes triggering a percept from those stabilizing it, we introduce tri-stable stimuli having three percepts. We find the probability and dominance duration of a percept independently adjustable. Percept probabilities and dominance durations show mutual dependencies across several perceptual switches. Consequently, the current perceptual experience depends on perceptual history; therefore, rivalry--even for continuous presentation--is not a memory-less process. Copyright 2010 Elsevier Ltd. All rights reserved.