Enduring interest in perceptual ambiguity: alternating views of reversible figures.

Research favoring the so-called bottom-up and top-down classes of explanations for reversible figures that dominated the literature in last half of the 20th century is reviewed. Two conclusions are offered. First, any single-process model is extremely unlikely to be able to accommodate the wide array of empirical findings, suggesting that the "final" explanation will almost certainly involve a hybrid conceptualization of interacting sensory and cognitive processes. Second, the utility of distinguishing between 2 components of the observer's experience with reversible figures is emphasized. This distinction between the observer's ability to access multiple representations from the single stimulus pattern (ambiguity) and the observer's phenomenal experience of oscillation between those representations (reversibility) permits the literature to be segregated into useful categories of research that expose overlapping but distinctive cortical processes.