1 Introduction Every view of our visual world gives rise to an infinite number of interpretations. Only through a series of inferential processes do we perceive a consistent and stable environment. These inferences occur so smoothly that they are rarely noticed. How- ever, certain stimuli can create problems for the visual system, and in so doing allow for a glimpse into the inferential processes. One such class of stimuli is ambiguous figures ösingle images that can give rise to multiple interpretations. For example, if you look at figure 1a, your percept should occasionally reverse, alternating between a `duck'and a `rabbit' (Jastrow 1899). Traditionally there have been two competing theories of how one's interpretation of an ambiguous figure reverses (for a recent review see Toppino and Long 2005), but this issue remains, at best, ambiguous. According to a satiation theory ambiguous-figure reversals occur though a process analogous to neuronal fatigue when perceiving color afterimages (eg Ko«hler 1940; Long and Toppino 1981). If you stare at a green color patch, and then shift your gaze to a white patch, you will perceive red. The initial exposure to green fatigues the firing `green neurons' and when you shift to the white patch, the `red neurons', which are not fatigued, dominate. Extending this analogy, perceiving a duck in figure 1a will eventually fatigue the neurons that represent the duck interpretation, giving way to the percept of a rabbit. Alternatively, a cognitive theory suggests that a reversal can occur only if an observer (a) knows the figure is ambiguous, (b) knows the two specific interpretations of the figure, and (c) has the intent to reverse (eg Girgus et al 1977; Rock and Mitchener 1992; Rock et al 1994a, 1994b). These competing theories map onto a `bottom ^ up' versus `top ^ down' debate, and they can be pitted against one another experimentally ösimply showing observers an unfamiliar ambiguous figure without telling them of its ambiguity. Will they spontane- ously perceive both interpretations? The satiation theory predicts that observers will spontaneously reverse between the possible percepts and the cognitive theory predicts they will not. Unfortunately, implementing this experiment has produced mixed results. When high-school students were shown ambiguous figures and told that they were reversible (but not informed of the possible alternatives), approximately one-half made a Reversing how to think about ambiguous figure reversals: Spontaneous alternating by uninformed observers Perception, 2006, volume 35, pages 709 ^ 715 Stephen R Mitroff, David M Sobelô, Alison Gopnik½ Center for Cognitive Neuroscience and Department of Psychological and Brain Sciences, Duke University, Box 90999, Durham, NC 27708, USA; e-mail: mitroff@duke.edu; ô Department of Cognitive and Linguistic Sciences, Brown University, Providence, RI 02912, USA; ½ Department of Psychology, University of California at Berkeley, Berkeley, CA 94720, USA Received 28 April 2005, in revised form 2 August 2005; published online 12 April 2005 Abstract. Ambiguous figures are a special class of images that can give rise to multiple inter- pretations. Traditionally, switching between the possible interpretations of an ambiguous figure, or reversing one's interpretation, has been attributed either to top ^ down or to bottom ^ up processes (eg attributed to having knowledge of the nature of the ambiguity, or to a form of neuronal fatigue). Here we present evidence that is incompatible with both forms of explanations. Observers aged 5^ 9 years can reverse ambiguous figures when uninformed about the ambiguity, negating purely top ^ down explanations. Further, those children who make these `spontaneous' reversals are more likely to succeed on a high-order theory-of-mind task, negating purely bottom ^ up explanations. DOI:10.1068/p5520