What is the speed of visual recognition memory?

Abstract

Investigations into the neural correlates of recognition memory suggest that there are two major sources of “recognition signals”, the rostral end of the visual ventral stream (rVVS) and the hippocampus. The rVVS is thought to support familiarity, a rapid context-free recognition signal, while the hippocampus is thought to support recollection, a slow context-rich recognition signal. In accordance, analyses of surface and intracerebral evoked potentials show a difference between familiar and unfamiliar stimuli starting ~250 ms in the rVVS, and ∼320 ms in the hippocampus. It remains controversial whether the rVVS can support recognition memory alone. If we add ~130 ms, the minimum time required to generate a motor response (Kalaska et Cramond, 1992 in the macaque), a response could occur around 380 ms based on the VVS and around 450 ms based on the hippocampus. To investigate the minimal time required for recognition memory, we designed a specific experiment to constrain participants to answer as quickly as they could. We used a Go/No-Go task with a response deadline 600 ms after stimulus onset (boosting speed) and an audio feedback for each response (boosting accuracy). We show that recognition of famous among unknown faces (120 targets/120 distractors) starts at 390 ms (min RT, hits different from false alarms (p < 0.05) for at least 2 consecutive bins of 10 ms, N = 8 participants). We ran the same experiment with two other categories of stimuli (abstract patterns and objects). Recognition of these stimuli was preceded by a self-paced study phase. Minimal RT for the abstract patterns and objects were 420 ms (N = 15) and 400 ms (N = 14), suggesting furthermore that verbalization and semantic content does not interfere with speeded visual recognition. These results support the idea that recognition can be based on the rostral visual ventral stream alone, in particular for rapid recognition.