GRUPO 4: ACCESS POINT, SW 24 PUERTOS, SW 8 PUERTOS

Both visual attention and visual working memory processes selectively activate and prioritize certain visual representations over others. However, with regards to working memory, this is possible in the absence of the actual stimulus (Olivers, Meijer, & Theeuwes, 2006). Thus, an object has a direct advantage in the competition for selective attention if its features have already been activated through a memory representation (Desimone & Duncan, 1995). Olivers et al. explored the possibility of

content-based memory-driven attentional capture. In their experiment, each trial commenced with the presentation of a disk, and in the memory conditions, participants were asked to remember the colour of the disk. This was followed by a visual search display which consisted of a number of disks and a diamond-shaped target. The target was not always the only unique item in the display, such that one of the distractors could also carry a unique colour; a singleton distractor (Pashler, 1988). Importantly, the singleton distractor, when presented, could carry the same colour as the to-be remembered item. The trial ended with a memory test, in which the participants were asked to choose the remembered colour from three presented colours. Performance in the memory condition was compared with a no-memory condition, in which participants were instructed to simply look at the initial coloured disk, without the need to remember it. They found that singletons captured attention, despite being detrimental to the task, but especially so under conditions of increased memory load. Thus, the additional memory task drained the cognitive control mechanism required to reject irrelevant distracting information (Olivers et al).

The capacity of working memory and visual attention was further examined by Lavie and de Fockert (2005) in a series of studies which manipulated working memory load. Specifically, they argued that the ability to prevent processing of irrelevant information is determined by the load of the working memory task. That is, goal-directed control of visual attention is possible when cognitive capacity is available to prevent processing of goal-irrelevant information. Lavie and de Fockert compared attentional capture by an irrelevant singleton in a visual search task between a single-task condition (a visual

search task) and a dual-task condition (a visual search task in addition to a working memory task). During the visual search task, participants searched for a circle among diamonds and were asked to respond to the orientation of a line within it. The presentation of an irrelevant colour singleton was varied across trials and attentional capture was determined by slower reaction times to the target when the singleton appeared. In the dual-task condition, working memory was manipulated by asking participants to rehearse either a set of six digits (experiment 1) or four digits in exact order (experiment 2) in order to decide whether a memory probe following the visual search task was present or absent in the memory set of that trial (experiment 1) or in order to recall a digit that followed the probe digit in the memory set (experiment 2).

Lavie and de Fockert (2005) found significantly greater singleton interference effects under conditions of high working memory load compared to no or low working memory load conditions. This suggested that working memory load determined visual search efficiency and also modulated attentional capture by irrelevant singleton distractors (Lavie & de Fockert). Based on these findings, they proposed that attentional capture may be determined by a combination of top-down and bottom-up processes. Thus, attentional control could be modulated by working memory and clearly implicated top-down control processes. However, a stimulus driven component also appeared to play a role such that an irrelevant singleton captured attention even when top-down control functions were not loaded (that is, in no-load or low-load conditions; Lavie & de Fockert).

de Fockert and colleagues (de Fockert, Rees, Frith & Lavie, 2001) also used a dual-task paradigm to demonstrate that manipulating working memory load could modulate distractor processing in a selective attention task. In their visual selective attention task, participants were asked to categorize famous written names as either politicians or pop stars while ignoring distractor faces which could either be congruent with the target name, incongruent with the target name, or anonymous. In the low working memory load task, participants were required to remember either a fixed order of digits, while in the high working memory load task, they were provided with a different order of digits on each trial. Participants were presented with the memory set which was followed by two, three, or four attention displays. Following the final attention display, a memory probe was presented and participants were required to report the digit that followed this probe in the memory set.

de Fockert et al. (2001) found that reaction times to the memory probe were faster in the low working memory load condition compared to the high working memory load condition (953ms and 1394ms respectively). Furthermore, in the selective attention task, distractor interference effects were significantly greater during high (78ms) than low (46ms) working memory load. de Fockert and colleagues argued that working memory plays a crucial role in actively maintaining stimulus-processing priorities in order to direct attention to relevant rather than irrelevant stimuli which subsequently minimized the interference effects of irrelevant distractors. This was further supported by their neuroimaging data which revealed that areas of prefrontal cortex involved in face processing were more activated in conditions of load, consistent with these areas

being sensitive to load and distractor interference (from the irrelevant faces). Collectively, these results supported their hypothesis that the availability of working memory is essential for top-down attentional control towards relevant information (de Fockert et al; see also de Fockert, Rees, Frith, & Lavie, 2004).

The preceding literature review highlights the relationship between working memory and selective attention. Firstly, working memory content aids efficient selective attention because attention is biased towards information in the internal template. Furthermore, the extent of distractor interference in a visual attention task is determined by the availability of cognitive resources.