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The visual environment can be dynamic and often changes from one moment to the next, causing sensory input to be noisy and uncertain. In addition, internal noise from neural activity in the brain contributes to this uncertainty. Despite these challenges, the brain’s visual system adeptly processes this noisy and uncertain information, creating a stable and continuous perceptual experience that allows us to navigate with a reliable sense of our environment. A phenomenon called serial dependence, in which the recent past is actively used to interpret what we are currently seeing, is thought to play a role in ensuring this perceptual stability and continuity.

Serial dependence occurs when current stimulus judgments are systematically
drawn towards recent stimulus history, so that a current stimulus is judged to be
more similar to a previous stimulus than it actually is. Serial dependence is known to occur for a variety of objects and features, including facial identity. Although serial dependence results in a misjudgment, it is thought to be beneficial and have a positive impact on facial recognition. The aim of my thesis was to investigate how perception and working memory contribute to serial dependence in facial identity. Paper I investigated the time course of serial dependence in facial identity from early perception to working memory stages in the context of task-related decisions. The main findings of Paper I show that merely perceiving a previous task-irrelevant face is sufficient to induce serial dependence and support the involvement of both perceptual and working memory processes in serial dependence in facial identity. Paper I further show that serial dependence in facial identity can be separated from
serial effects arising from stimulus interactions within working memory.

In Paper II, electroencephalogram was used to investigate the relation between serial dependence and working memory capacity. Results show that in the context of dual-task demands, individual differences in working memory capacity predict serial dependence in terms of selective suppression of task-irrelevant and selective maintenance of task-relevant information. Working memory is closely intertwined with perception. Electroencephalogram and a dual-task were also used in Paper III to investigate the interactive contribution of perception and working memory to serial dependence. The results further support selective suppression as a mechanism contributing to serial dependence as well as mechanisms such as perceptual capacity, recollection, post-retrieval monitoring and working memory maintenance, operating in part jointly and independently on different time scales.

The present thesis contributes to understanding how perceptual and working memory mechanisms underlying serial dependence operate to achieve stability and continuity by actively smoothing the appearance of faces across brief temporal delays, with the specific aim of stabilizing judgments of facial identity.