Far from being a faithful, static representation of external reality, our perception results from a balanced combination of expectations and prior experience with incoming sensory information. Spatial and temporal context constantly shape our perception and the underlying neural responses in a way that can be related to the statistical structure of the inputs (Schwartz et al., 2007). This active shaping of perception is particularly critical when the ambiguity of the stimulus does not allow a univocal interpretation of external inputs, and behaviourally a decision is required that resolves the uncertainty. How the immediate temporal context modulates visual processing, in particular, has been investigated through studies of adaptation aftereffects. Prolonged exposure (adap- tation) to a stimulus can influence the perception of a ABSTRACT Sensory information from the external world is inherently ambiguous, necessitating prior experience as a constraint on perception. Recent experience with clear, prototypical stimuli may, however, induce complex effects on the subsequent perception of ambiguous ones, ranging from attraction (priming) to repulsion (adaptation aftereffects). In the present study, we ask what determines the direction and magnitude of the effects in the case of images of naturalistic (complex) objects, which are putatively analyzed in advanced visual cortices and under the influence of multimodal semantic memories. We find a basic crossover from adaptation aftereffects to priming effects as the delay lengthens between experiencing a prototype and seeing the ambiguous stimulus. Adaptation aftereffects appear as a shift in the perceptual boundary between distinct object images, which vanishes with time, unmasking an overall and temporally sustained priming bias. A similar attractive bias occurs when the original adapter is substituted by an ambiguous image.