Conscious and nonconscious memory effects are temporally dissociable

Abstract

Intentional (explicit) retrieval can reactivate sensory cortex, which is widely assumed to reflect conscious processing. In the present study, we used an explicit visual memory event-related potential paradigm to investigate whether such retrieval related sensory activity could be separated into conscious and nonconscious components. During study, abstract shapes were presented in the left or right visual field. During test, old and new shapes were presented centrally and participants classified each shape as "old-left", "old-right", or "new". Conscious activity was isolated by comparing accurate memory for shape and location (old-hits) with forgotten shapes (old-misses), and nonconscious activity was isolated by comparing old-left-misses with old-right-misses and vice versa. Conscious visual sensory activity had a late temporal onset (after 800 ms) while nonconscious visual sensory activity had an early temporal onset (before 800 ms). These results suggest explicit memory related sensory activity reflects both conscious and nonconscious processes that are temporally dissociable.

Figure 1

(A) Study phase. (B) Test phase (accurate labels shown to the right).

Figure 2

(A) Old-left-hit – old-right-hit (top panel) and old-right-hit – old-left-hit (bottom panel) activation timecourses in left occipital, left temporal, right occipital, and right temporal regions-of-interest (ROIs; color key to right). Significant lateralized activity in right occipital and right temporal ROIs is shown by red and yellow (overlap in orange) vertical bars, respectively, while significant lateralized activity in left occipital and left temporal ROIs is shown in blue and green (overlap in cyan) vertical bars, respectively. (B) Old-left-hit – old-right-hit (top panels) and old-right-hit – old-left-hit (bottom panels) lateralized activity in occipital and temporal regions-of-interest (ROIs). (C) Voltage topographies at early time points illustrating retinotopic/contralateral activity (posterior view, color scale at center; ovals demarcate ROIs).

Figure 3

(A) Old-left-hit – old-left-miss (top panels) and old-right-hit – old-right-miss (bottom panels) lateralized conscious activity. (B) Old-left-miss – old-right-miss (top panels) and old-right-miss – old-left-miss (bottom panels) lateralized nonconscious activity.

Figure 4

(A) Old-left-hit – new-correct rejection (top panels) and old-right-hit – new-correct rejection (bottom panels) lateralized activity in occipital and temporal ROIs. (B) Old-left-miss – new-correct rejection (top panels) and old-right-miss – new-correct rejection (bottom panels) lateralized nonconscious activity.