Attractive serial dependence between memorized stimuli

Attractive serial dependence - a bias whereby the current stimulus appears more similar to the previous ones - is thought to reflect a stability mechanism integrating past and current visual signals. Prior work suggests that serial dependence originates from both perceptual and cognitive mechanisms, but the conditions under which this attractive bias occurs remain to be studied. In particular, whether serial dependence can occur solely from memory interference remains unclear. Here, we address this question by testing the hypothesis that if memory interference is sufficient to generate serial dependence, it should occur within memorized stimuli irrespective of the order of stimulus presentation. In Exp. 1, we used a numerosity estimation task in which participants estimated the number of dots of a briefly flashing dot-array comprising 8 to 32 dots. The pattern of serial dependence was found in that numerical estimates of a dot array were biased towards the numerosity of the preceding dot array. In Exp. 2, we presented a series of three such dot arrays, and cued the one to be estimated only after the whole series was presented, making the participants first form a memorized representation of the three dot arrays. The results show a pattern of attractive biases both in the forward (the stimulus presented before biases the one presented after) and the backward (the stimulus presented after biases the one presented before) directions. Overall, our results demonstrate that serial dependence can be induced solely from memory interference and that this interference can operate irrespective of the chronological order of the stimulus presentation.