Forgetting over the short-term has challenged researchers for more than a century, largely because of difficulty in controlling what goes on within the memory retention interval. But the Òrecent negative probesÓ procedure offers a valuable paradigm, by examining influences of (presumably) unattended memoranda from prior trials. Here we used a recent probes task to investigate forgetting for visual non-verbal short-term memory. Target stimuli (2 visually presented abstract shapes) on a trial were followed after a retention interval by a probe, and participants indicated whether the probe matched one of the target items. Proactive interference, and hence memory for old trial probes, was observed whereby participants were slowed in rejecting a nonmatching probe on the present trial that nevertheless matched a target item on the previous trial (a recent negative probe). The attraction of the paradigm is that, by uncovering proactive influences of past trial probe stimuli, it is argued that active maintenance in memory of those probes is unlikely. In two experiments we recorded such proactive interference of prior trial items over a range of interstimulus (ISI) and intertrial (ITI) intervals (between 1 and 6 seconds respectively). Consistent with a proposed t w o -process memory conception (the active-passive memory model or APM), actively maintained memories on current trials decayed but passively Òmaintained,Ó or unattended, visual memories of stimuli on past trials did not.(abstract 221 words)

Humans have the ability to attentionally select the most relevant visual information from their extrapersonal world and to retain it in a temporary buffer, known as visual short-term memory (VSTM). Research suggests that at least two non-contiguous items can be selected simultaneously when they are distributed across the two visual hemifields. In two experiments, we show that attention can also be split between the left and right sides of internal representations held in VSTM.Participants were asked to remember several colors, while cues presented during the delay instructed them to orient their attention to a subset of memorized colors. Experiment 1 revealed that orienting attention to one or two colors strengthened equally partic colors, but only when they were from separate hemifields. Experiment 2 showed that in the absence of attentional cues the distribution of the items in the visual field per se had no effect on memory.These findings strongly suggest the existence of independent attentional resources in the two hemifields for selecting and/or consolidating information in VSTM. 3The ability to maintain visual information in an accessible state is a critical aspect of our cognitive capacities as it allows us to interact successfully in the visuo-spatial world. Because our visual short-term retention system (i.e., visual short-term memory -VSTM) is extremely limited in storage capacity (Luck & Vogel, 1997), only a subset of information from our extrapersonal world can be transferred into this limited memory space at any one time. The selection of this subset of information is made by attentional mechanisms that can be voluntarily or involuntarily oriented to particular locations or objects. For example, when spatial attention is cued to a particular location of the visual field, the object that occurs at that location will be more likely transferred into VSTM as compared to the other objects (Makovski & Jiang, 2007;Schmidt, Vogel, Woodman, & Luck, 2002).During the last 10 years, an increasing number of studies have revealed that once transferred into VSTM, the internal representations remain highly flexible and can be selectively accessed and , directing attention to one location previously occupied by an object helps solidify and/or retrieve that object from memory. However, this ability to attentionally select locations already held in VSTM appears to be more constrained than orienting attention in perception. In a recent study, Makovski and Jiang (2007) directly compared the effect of orienting attention to multiple locations before (pre-cuing) and after (retro-cuing) the appearance of a memory array. They found that while up to three attentional cues could be used effectively when presented before the memory array, 4 only a single cue was advantageous for memory performance when presented after the offset of the memory array. Although this, along with previous studies (Awh & Pashler, 2000;Kraft, Müller, Hagendorf, Schira, Dick, Fendrich, & Brandt, 2004; Kramer & Haln, 1995), indicates that spati...

Recent research on visual short-term memory (VSTM) has revealed the existence of a bilateral field advantage (BFA -i.e., better memory when the items are distributed in the two visual fields than if they are presented in the same hemifield) for spatial location and bar orientation, but not for colour (Delvenne, 2005; Umemoto, Drew, Ester, & Awh, 2010). Here, we investigated whether a BFA in VSTM is constrained by attentional selective processes. It has indeed been previously suggested that the BFA may be a general feature of selective attention (Alvarez & Cavanagh, 2005;Delvenne, 2005). Therefore, the present study examined whether VSTM for colour benefits from bilateral presentation if attentional selective processes are particularly engaged. Participants completed a colour change detection task whereby target stimuli were presented either across both hemifields or within one single hemifield. In order to engage attentional selective processes, some trials contained irrelevant stimuli that needed to be ignored. Targets were selected based on spatial locations (Experiment 1) or on a salient feature (Experiment 2). In both cases, the results revealed a BFA only when irrelevant stimuli were presented amongst the targets. Overall, the findings strongly suggest that attentional selective processes at encoding can constrain whether a BFA is observed in VSTM.

Research has shown that attentional pre-cues can subsequently influence the transfer of information into visual short term memory (VSTM) (Schmidt, B., Vogel, E., Woodman, G., & Luck, S. (2002). However, those effects were only shown when the pre-cues were directed to stimuli displayed across hemifields relative to stimuli within a single hemifield. Importantly, the results were not replicated when participants were required to memorise colours (Experiment 2) or locations (Experiment 3) in the absence of spatial pre-cues. Those findings strongly suggest that attentional pre-cues have a strong influence on both the transfer of information in VSTM and its subsequent maintenance, allowing bilateral items to better survive decay.