Sujin Kim, David Burr, Guido Marco Cicchini, David Alais
Serial dependence in perception requires conscious awareness
Current Biology 30, R237–R262, March 23, 2020
Current visual perception is systematically biased towards the immediate past, an effect known as serial dependence. A variety of basic visual features, including orientation, motion and numerosity, show serial dependence, but it remains unclear whether perceptual awareness is necessary. We address this question by combining serial dependence for orientation with binocular rivalry between orthogonal gratings. Fourteen participants viewed trial sequences which alternated between rivalrous presentations, with orthogonal gratings to each eye, and monocularly presented test gratings. Participants indicate the orientation of the stimuli – either the dominant percept in rivalry or the orientation of the test – by matching with a rotatable line. Half of the rivalry trials were selected (at random) for the “dominant” condition, half for the “supressed” condition. The subsequent test was presented to the appropriate eye (dominant or suppressed) at an orientation rotated ±10° from the chosen rivalrous stimulus. We found that orientation estimates were strongly biased towards the preceding trial (positive serial dependence), but only in the dominance condition, not in the suppression condition. These results were replicated with test gratings presented binocularly in a separate experiment. These results show that only if stimuli are consciously perceived will they act as a prior to bias subsequent perception, suggesting that construction of the prior occurs at a relatively high level. However, the results do not speak to the issue of the stage of analysis where the prior distorts incoming sensory information.