Episodic Memory: What's Consciousness Got to Do with It?

Abstract

Episodic memory is the memory for experienced events. A peak competence of episodic memory is the mental combination of experienced events to infer commonalities. This enables adequate interpretation and behavior. Inferring commonalities in episodic memory may proceed with and without consciousness of events. Yet, what distinguishes conscious from unconscious event encoding? This question inspired nine experiments that featured strongly and weakly masked cartoon clips presented for unconscious and conscious encoding and inference. Each clip featured a scene with a visually impenetrable hiding place. Five animals crossed the scene one-by-one consecutively. One animal trajectory represented one event. The animals moved through the hiding place, where they might linger or not. Participants’ task was to observe the animals’ entrances and exits to maintain a mental record of which animals hid simultaneously. We manipulated information load to explore capacity limits of conscious/unconscious encoding. Memory of inferences was tested immediately or 3.5 or 6 minutes following encoding. Participants retrieved inferences well when encoding was conscious. When encoding was unconscious, participants needed to give retrieval responses intuitively. Only habitually intuitive decision-makers exhibited significant delayed retrieval of inferences drawn unconsciously. Hippocampal activity increased with correct retrieval responses and correlated with retrieval success at both consciousness levels. With increasing information load, delayed retrieval performance remained only stable when encoding had been unconscious. A strong hippocampal-neocortical functional connectivity hallmarked conscious memories. A sparse coding hallmarked unconscious memories. Sparse coding may have enlarged memory capacity. Hence, levels of consciousness influenced the memories’ behavioral impact, representational code, and memory capacity.