Academic journal article Memory & Cognition

The Contents of Visual Memory Are Only Partly under Volitional Control

Academic journal article Memory & Cognition

The Contents of Visual Memory Are Only Partly under Volitional Control

Article excerpt

When we look around within a visual scene, is visual information automatically placed in visual memory during each saccade, or can we control which information is retained and which is excluded? We examined this question in five experiments by requiring participants to remember sequentially presented visual shapes or faces-some of which were marked for encoding (targets) and others that were supposed to be ignored (distractors)-over a 1-sec delay. The results show that distractors were retained in visual memory, regardless of stimulus category, suggesting that it is a general phenomenon. Whether or not participants were allowed to prepare for a target or distractor did not modulate distractor intrusion. When attention coupled with eye movements could be used to select targets, distractors were no longer encoded into memory. When eye movements were constrained, distractors once again intruded into memory. These findings suggest that top-down control processes are insufficient to filter the contents of visual memory.

The goal of this article is to gain a foothold in understanding the role of visual attention in visual memory. One role of attention is to act as a gatekeeper by selecting which objects will be consolidated into visual memory. Palmer (1990) studied this by requiring participants to remember line lengths over short durations under two different encoding conditions: one in which participants were required to remember two cued items out of four items in the memory display, or one in which they had to remember two items out of two items on the memory display. The results showed that attention biased which information did and did not enter visual working memory (VWM), because instructions to remember a subset of items in a display with distractors led to memory performance equivalent to that for just showing the subset with no distractors. In other words, distractors did not intrude into VWM (Palmer, 1990). Jiang, Olson, and Chun (2000; Experiment 4B) found similar effects of attention on VWM for colors.

Other studies have shown that shifts of attention to cued locations can enhance the transfer of information that resides at that location into iconic memory. In early studies of iconic memory, participants were presented with a brief array of alphanumeric characters and were asked to report all of the characters-the whole-report condition-or a subset of cued characters-the partial-report condition. The cue, either a tone or a visual mark, was presented after the array of characters, and it indicated which characters to report. The results showed that recall of characters was accurate for arrays of four to five characters in the whole-report condition. In contrast, performance was highly accurate for large array sizes in the partial-report condition. These findings suggest that participants used the cue in the partial-report condition to selectively transfer the cued characters into iconic memory (Averbach & Coriell, 1961; Sperling, 1960). A study of a later stage of mnemonic processing, VWM, found that precues cause shifts of attention that bias which information is transferred to VWM (Schmidt, Vogel, Woodman, & Luck, 2002), suggesting that bottom-up attentional processes also affect which information enters VWM.

Attention may also be important during memory maintenance, to help sustain information over delays. Several studies have now shown that when sample stimuli are followed by an attentional cue, memory for the cued items is enhanced (see, e.g., Griffin & Nobre, 2003). This suggests that VWM representations are volatile and prone to degradation unless they receive the benefits of focused attention (Makovski, Sussman, & Jiang, 2008).

However, it is not known whether visual attention is the sole determinant of what does and does not enter visual memory. It is possible that even when an item is visually attended, participants can still exert control over its entry into memory. …

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