Clashing Memories: Interference in Working Memory modulates Serial Dependence

Visual perception reflects a combination of current input, past information, and expectations. Serial dependence describes how prior and present stimuli interact, often resulting in attractive biases toward previously seen inputs, particularly under uncertainty about the incoming stimulus feature. While prior work manipulated noise by manipulating stimulus properties, here we directly altered the quality of internal representations using an intermediate task performed during the retention interval. Participants viewed oriented Gabor patches and reproduced their orientation after a delay. During that delay, they completed one of several intermediate tasks: judging the size of circles (containing no orientation information), the length or orientation of lines, the frequency of tones, or no task (Control condition). These manipulations allowed for a detailed assessment of the role of working memory load and inter-item competition in memory on the precision of the encoded Gabor orientation and subsequently, on the strength of serial dependence. Results showed that any intermediate task which required encoding more stimuli in working memory increased the strength of serial dependence. This bias was present even with an auditory task. Because memory precision often decreases when more items need to be encoded, this reduction in precision can explain why serial dependence increased under higher working memory load. However, sharing the same feature dimension (e.g., orientation) did not further increase serial dependence, though it did increase response variability. These findings offer novel evidence that degraded memory precision, not just stimulus noise, enhances biases towards past input, shaping serial dependence through internal uncertainty. Furthermore, it highlights the interdependence between serial dependence and visual working memory.