Accumulating behavioral and neural evidence suggests that incoming sensory input is represented and combined with generalized semantic knowledge in a fundamentally probabilistic way during perceptual processes. Recently we provided evidence that human perceptual decision making is fully probabilistic (encodes uncertainty of all internal variables) rather than task-dependently probabilistic (encoding uncertainty only at the level of decision variables). However, episodic memories are traditionally treated outside of this perceptual context. Hence, it is unknown if episodic memories are also treated probabilistically, that is, whether they are encoded and recalled with their uncertainty just as immediate sensory information is. To address this question, we conducted an episodic memory study, in which participants (N=76) first viewed a set of objects presented either individually or in scenes and later they had to recall the orientation of those objects and indicate their uncertainty about their responses. We used the well-calibratedness of orientation responses, i.e., the level of positive correlation between participants’ subjective certainty and orientation accuracy as the indicator of the probabilistic encoding of episodic memory. Our results showed a recall performance with object orientation substantially lower than performances reported in earlier studies with semantic features. This indicates that memory is not equally massive for all object dimensions. More importantly, at any time when orientation recall accuracy was significantly above chance, the participant’s responses became well-calibrated with highly significant positive correlations between participants’ subjective certainty and orientation accuracy for both individually presented objects (p < .004, BF = 10.2) and for objects presented in scenes (p < .001, BF > 100). These results suggest that encoding and recall of long-term episodic memory follow the same probabilistic principles as perception. This allows the momentary perceptual input, semantic knowledge and individual episodic memory traces to be treated and combined in a fundamentally uniform manner in the brain.

 

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