Generating visual mental images: latency and vividness are inversely related.

In three experiments, participants pressed a reaction time key and rated vividness after reading descriptions of common objects and imagining them as accurately as possible within a visual display subtending 1.2 degrees or 10.8 degrees. Display size had small effects on vividness and on image latency. Latency was much faster (approximately 2.5 sec) for vivid images than for nonvivid ones (approximately 7.5 sec), regardless of display size and initial size at which the images were generated (natural image size). Our findings characterize images as (1) detailed, as indicated by ratings of detail and by lack of category membership effects; (2) as occurring at many natural image sizes, so that time-consuming size adjustments are typically not needed; and (3) generated not concurrently with but after lexical access, as shown by latencies for the same image evoked by synonyms like pail and bucket. We conclude that image vividness and latency reflect the activation level of the visual imagery system, implying that image generation in everyday life mostly involves retrieving already-computed representations episodically stored in memory, which seldom require extensive re-elaboration such as size adjustment.