Visual long-term memory is not unitary: Flexible storage of visual information as features or objects as a function of affect

Research has shown that observers store surprisingly highly detailed long-term memory representations of visual objects after only a single viewing. However, the nature of these representations is currently not well understood. In particular, it may be that the nature of such memory representations is not unitary but reflects the flexible operating of two separate memory subsystems: a feature-based subsystem that stores visual experiences in the form of independent features, and an object-based subsystem that stores visual experiences in the form of coherent objects. Such an assumption is usually difficult to test, because overt memory responses reflect the joint output of both systems. Therefore, to disentangle the two systems, we (1) manipulated the affective state of observers (negative vs. positive) during initial object perception, to introduce systematic variance in the way that visual experiences are stored, and (2) measured both the electrophysiological activity at encoding (via electroencephalography) and later feature memory performance for the objects. The results showed that the nature of stored memory representations varied qualitatively as a function of affective state. Negative affect promoted the independent storage of object features, driven by preattentive brain activities (feature-based memory representations), whereas positive affect promoted the dependent storage of object features, driven by attention-related brain activities (object-based memory representations). Taken together, these findings suggest that visual long-term memory is not a unitary phenomenon. Instead, incoming information can be stored flexibly by means of two qualitatively different long-term memory subsystems, based on the requirements of the current situation.