Expectations about presence enhance the influence of content-specific expectations on low-level orientation judgements.

Will something appear and if so, what will it be? Perceptual expectations can concern both the presence and content of a stimulus. However, it is unclear how these different types of expectations interact with each other in biasing perception. Here, we tested how expectations about stimulus presence and content differently affect perceptual inference. Across separate online discovery (N = 110) and replication samples (N = 218), participants were asked to judge both the presence and content (orientation) of noisy grating stimuli. Crucially, preceding compound cues simultaneously and orthogonally predicted both whether a grating was likely to appear as well as what its orientation would be. Across both samples we found that content cues affected both discrimination and presence judgements directly, namely by biasing the orientation judgements in the expected direction and enhancing confidence in stimulus presence on congruent trials. In contrast, presence cues did not affect discrimination judgements directly. Instead, presence cues influenced discrimination judgements indirectly by enhancing the effect of the orientation cues when expecting a stimulus to be present. This was the case on trials where a stimulus was present, as well as on grating-absent trials. Further, presence cues directly affected confidence in stimulus presence. This suggests that presence expectations may act as a regulatory volume knob for the influence of content expectations. Further, modelling revealed higher sensitivity in distinguishing between grating presence and absence following absence cues than presence cues, demonstrating an asymmetry between gathering evidence in favour of stimulus presence and absence. Finally, evidence for overweighted expectations being associated with hallucination-like perception was inconclusive. In sum, our results provide nuance to popular predictive processing accounts of perception by showing that expectations of presence and content have distinct but interacting roles in shaping conscious perception.