What Makes Memories Vivid?

Some memories are vivid and detailed, while others are vague and indistinct. Although a common experience, the cognitive mechanisms underlying these differences remain poorly understood. A common explanation for what makes mental representations vivid is their shared properties with visual perception. However, recent research has shown that semantic properties of stimuli strongly influence their representations. To determine the extent to which visual and/or semantic properties influence memory vividness, we first examined whether individual stimuli reliably elicit similar subjective feelings of vividness across different subjects. Next, we explored how vividness relates to visual (i.e., color and brightness) and semantic (i.e., taxonomic category) properties of naturalistic images (Experiment 1). We found that vividness ratings were consistent across subjects; crucially, this consistency depended not only on the visual properties of the stimuli but also on their semantic properties. We then employed Deep Neural Networks to select stimuli based on their visual or semantic features (Experiment 2). Our results showed that stimuli selected for their semantic—but not those selected purely for their visual—properties reliably elicited vivid memories. Finally, we demonstrated that even in a purely visual recall test (Experiment 3), where both encoding and retrieval operations focused exclusively on the visual properties of a mnemonic cue, memory vividness still depended on the integration of visual and semantic stimuli representations. Together, our findings demonstrate, at multiple levels of inference, that although vividness is often compared to perception, this subjective quality of memory is shaped by our knowledge of the world.