Effects of perceptual and decisional uncertainty on serial dependence in orientation perception.

Where assimilative serial dependence occurs in perception, responses to visual attributes such as orientation are typically biased towards the attributes of visual stimuli seen in the recent past. Serial dependence is thought to increase the signal-to-noise ratio of visual representations and is reliably increased by uncertainty in the target stimulus. However, the amount of uncertainty in the preceding inducer stimulus does not seem to modulate serial dependence. Here, we consider whether uncertainty in the decision made about the inducer stimulus modulates serial dependence instead by using stimuli with high positive evidence (high-contrast signal plus high-contrast noise) and low positive evidence (low-contrast signal and low-contrast noise). Such stimuli are matched in their signal-to-noise ratio but differ in overall contrast, and have been found to modulate response confidence but not response accuracy. Thirty-three participants viewed oriented Gabor patches presented under different levels of signal-to-noise ratio and positive evidence and reported their orientation, as well as their response confidence. We found that serial dependence was greatest for target stimuli that had low signal-to-noise ratio, low positive evidence, or were responded to with low subjective confidence. We find no modulation of serial dependence by uncertainty of any kind in the inducer trial. This finding suggests that serial dependence may not reflect a bias towards previous decisions, and has implications for wider theoretical accounts of serial dependence. The data and materials for this experiment are available via the Open Science Framework at https://osf.io/kvy4c/.