Abstract
Does visual information enjoy automatic, obligate entry into memory or, after such information has been seen, can it still be voluntarily excluded? To answer the question, we measured visual episodic recognition memory for series of compound grating stimuli whose horizontal and vertical spatial frequencies varied. Because recognition declines as additional study items enter memory, episodic recognition performance provides a sensitive index of memory's contents. A set of experiments showed that subjects had considerable success in excluding from memory any stimulus occupying a particular serial position in a series of study items.
Successful exclusion did not depend upon low-level information, such as stimulus orientation, contrast; also it did not depend upon location-specific attention or change in gaze. Additionally, exclusion did not require consistent, predictable timing of components within the simulus sequence. This last result suggests that the exclusion process is gated, in part, by the onset of the to-be-excluded stimulus.
To identify the stage(s) at which voluntary amnesia might operate, we analyzed key results within the framework of a summed similarity model for visual recognition model (NeMO; Kahana & Sekuler, Vision Research 2002). This analysis revealed that even when an study item seemed to have been excluded from recognition memory, its spatial frequency content still strongly influenced recognition memory for other study items. This result suggests that exclusion operates after considerable visual processing of the to-be-excluded item.
Supported by AFOSR Award F49620-03-1-0376 and NIH grant MH068404.