Publication
In serial dependence (SD), perceptual decisions deviate toward the recent past: the orientation of a visual stimulus is reported as more similar to the orientation of previous stimuli than it really is. At present, this phenomenon has always been reported in the presence of physical stimuli. As a result, SD has been mostly interpreted as reflecting a mechanism that stabilizes perception by combining prior and present visual input. Here we demonstrate that physical stimuli are not a prerequisite and SD can occur in the total absence of visual input. In two experiments, we asked participants to imagine and reproduce an orientation cued by a numeric digit and then to reproduce the orientation of a real Gabor patch. In Experiment 1, participants reproduced the imaginary and then the physical orientation in each trial. In Experiment 2, we additionally presented an irrelevant physical Gabor that participants had to ignore while imagining the cued orientation. Mental imagery in the lack of physical visual input led to strong SD: only the imagined orientation biased the report of a physical one, but not the other way around. Even more, the irrelevant stimulus presented at the time of the imagined orientation caused a repulsive bias in the following decision. Hence, SD occurs in the pure absence of visual input, suggesting that the integration of prior and present information resides at the level of abstract representations rather than low-level physical features.