Short term memory

Short term Memory

Introduction

Visual short-term memory (VSTM) retains objects and scenes for a few seconds after their disappearance (Luck & Vogel, 1997). Unlike iconic memory, which is disrupted by subsequent visual input, VSTM is traditionally considered a robust form of visual memory whose contents can survive changes in screen location, eye position, observer motion, and object occlusion (Phillips, 1974). This view leads to the proposal that VSTM helps maintain visual stability by bridging across spatiotemporal interruptions. However, recent studies have shown that contents in VSTM are highly vulnerable to interference from subsequent displays, including images that require memory (Broadbent & Broadbent, 1981) or attention (Landman, Spekreijse, & Lamme, 2003) and images that are passively viewed (Makovski, Shim, & Jiang, 2006). But in what respect is VSTM representation enhanced? In a separate study, Landman et al. (2003) also discovered that retrospectively cuing an item in VSTM enhances change detection performance. Landman et al. propose that visual information is initially held in a high capacity store known as a cortical icon (Sligte, Lamme, & Scholte, 2006), which is distinguished from iconic memory by its long duration. This memory is easily interfered with by a postchange test display, unless attention has already focused on one of the memorized items. In this study, we ask, is the robustness of VSTM modulated by selective attention? If so, what are the boundary conditions for this modulation? In Griffin and Nobre's study, for example, an attentional orienting cue is presented either before memory encoding, or after memory encoding. The cue informs observers which item will later be probed. Compared with no-cue trials, cuing attention to the potential target increases memory performance. This effect is found both when attention is directed in perceptual space (cue before memory encoding), and when it is directed in VSTM (cue 2-12 sec after memory encoding; Lepsien et al., 2005). To account for the benefit of orienting attention in VSTM where all items are already attended, Griffin and Nobre propose that focused attention enhances VSTM representation at the cued location. Whether short-term visual memory indeed contains an initial phase of a highcapacity store remains controversial. However, Landman et al.'s study suggests that selective attention enhances VSTM representation by increasing its robustness to subsequent interference. Although this proposal is plausible, it lacks direct empirical evidence. Griffin and Nobre (2003) did not manipulate interference directly, and Landman et al. simply assumed that interference came from the postchange test display. Yet Landman et al. could not directly assess interference effects because their test array served both as a probe for memory and as a source of Distributing versus focusing attention in visual short-term memory Visual short-term memory (VSTM) is traditionally considered a robust form of visual memory resistant to interference from subsequent visual input.

This study aims to directly test the hypothesis that selective attention modulates the robustness of VSTM.

If orienting attention to an item in VSTM increases its robustness, then interference from the irrelevant array should be eliminated when attention is focused on that ...