The representational similarity between visual perception and recent perceptual history.

From moment to moment, the visual properties of objects in the world fluctuate due to external factors like ambient lighting, occlusion and eye movements, and internal (proximal) noise. Despite this variability in the incoming information, our perception is stable. Serial dependence, the behavioral attraction of current perceptual responses towards previously seen stimuli, may reveal a mechanism underlying stability: a spatio-temporally tuned operator that smoothes over spurious fluctuations. The current study examined the neural underpinnings of serial dependence by recording the electroencephalographic (EEG) brain response of female and male human observers to prototypical objects (faces, cars and houses) and morphs that mixed properties of two prototypes. Behavior was biased towards previously seen objects. Representational similarity analysis revealed that responses evoked by visual objects contained information about the previous stimulus. The trace of previous representations in the response to the current object occurred immediately upon object appearance, suggesting that serial dependence arises from a brain state or set that precedes processing of new input. However, the brain response to current visual objects was not representationally similar to the trace they leave on subsequent object representations. These results reveal that while past stimulus history influences current representations, this influence does not imply a shared neural code between the previous trial (memory) and the current trial (perception). Significance statement The perception of visual objects is pulled towards instances of that object seen in the recent past. The neural underpinnings of this serial dependence remain to be fully investigated. The present study examined EEG responses to faces, cars and houses, and ambiguous between-category morphs. With representational similarity analysis, we showed (1) object-specific neural patterns that differentiate the three categories; (2) that the response to the current object contains information about the previous object, mirroring behavioral serial dependence; (3) that the object-specific neural pattern about the past was different from that in the current response, revealing that while past stimulus history influences current representations, this does not imply a shared neural code between the previous trial (memory) and the current trial (perception).