The influence of prior information on hallucinatory perceptions in healthy observers

Our subjective experience of the world as visually rich and detailed appears inconsistent with phenomena like change blindness and inattentional blindness. These illustrate that, in the absence of focused attention, individuals are prone to missing changes or objects that would otherwise be noticed. These findings suggest that attention is crucial for conscious perception, raising the possibility that our experience of visual richness might be an illusion. However, other studies found that healthy participants sometimes report seeing an absent object that was previously present when their attention is engaged otherwise. We investigated how prior information that an object will be absent influences the occurrence and of such non-veridical perceptions. Participants mainly engaged in a demanding visual task with peripheral stimuli and only occasionally (20% of trials) had to report the roof color of a house in a natural scene presented at the center of the display. Crucially, we used scenes with the same gist that contained a house, except for the last trial, which showed a scene without a house. Directly after participants finished, we asked them to describe what they saw in the last trial. One group of participants was informed that there will be no house in the last trial, while the other group was kept naïve. Preliminary results showed that many naïve participants did not notice the absence of the house, and some reported seeing a house (instead of guessing there was one). Surprisingly, informed participants were not immune to these effects. These findings support the view that conscious perception does not require attention and provide evidence for constructive top-down effects on conscious perception when sensory information is limited (e.g., when attention is engaged otherwise).