Abstract
Recent work has established that visual working memory is subject to serial dependence: current information in memory blends with that from the recent past as a function of their similarity. This tuned temporal smoothing likely promotes the stability of memory in the face of noise and occlusion. Serial dependence accumulates over several seconds in memory and deteriorates with increased separation between trials. While this phenomenon has been extensively characterized in behavior, its neural mechanism is unknown. In the present study, we investigate the circuit-level origins of serial dependence in a biophysical model of cortex. We explore two distinct kinds of mechanisms: stable persistent activity during the memory delay period and dynamic “activity-silent” synaptic plasticity. We find that networks endowed with both strong reverberation to support persistent activity and dynamic synapses can closely reproduce behavioral serial dependence. Specifically, elevated activity drives synaptic augmentation, which biases activity on the subsequent trial, giving rise to a spatiotemporally tuned shift in the population response. Our hybrid neural model is a theoretical advance beyond abstract mathematical characterizations, offers testable hypotheses for physiological research, and demonstrates the power of biological insights to provide a quantitative explanation of human behavior.
Highlights
Standard paradigms for measuring the contents of visual working memory have revealed that human observers tend to merge features of stimuli from previous trials into their representation of the current one, leading to a systematic bias in behavioral reports [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
While it has been proposed that serial dependence directly alters stimulus perception [1, 8]—and precedes the onset of memory or decision making [1, 8]—more recent studies have demonstrated that the trial-history bias is absent at the time of perception [9, 15] and evolves slowly during the subsequent delay period of a working memory task [9, 15, 17, 18], reaching an asymptote
Cognitive scientists have debated for years whether distinct items in working memory are arranged in discrete slots or assigned continuous resources [54,55,56,57]
Summary
Standard paradigms for measuring the contents of visual working memory have revealed that human observers tend to merge features of stimuli from previous trials into their representation of the current one, leading to a systematic bias in behavioral reports [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. While it has been proposed that serial dependence directly alters stimulus perception [1, 8]—and precedes the onset of memory or decision making [1, 8]—more recent studies have demonstrated that the trial-history bias is absent at the time of perception [9, 15] and evolves slowly during the subsequent delay period of a working memory task [9, 15, 17, 18], reaching an asymptote
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