The paper "Working Memory Encoding Delays Top-Down Attention to Visual Cortex by Scalf, Dux & Marois" is a delightful example of an article on medical science. A number of scientists have dedicated their time to understand how the human brain functions and how the mind works. An important component that is under scrutiny is the Working Memory, a short term component that is responsible for the processing of information. The working memory has a limited capacity, and scientists are interested in how it completes different processes when they occur concurrently or sequentially.
Research shows that when WME is engaged, it delays perceptual processing by using executive resources. In a bid to understand whether a previous task that that engages working memory encoding (WME) interferes with or delays top-down attentional responses to a second task, Scalf, Dux & Marois (2011) conducted three experiments that tested the effect of WME on a subsequent task. It was hypothesized that when the first task required a lot of resources, it would inhibit attention to the top-down sensory processing in the extrastriate cortex for the second task.
Conducting the Study For this experiment, data were collected on task accuracy and speed for both T1 and T2. Data was also collected using fMRI to study brain activation during different tasks. In the first experiment, 14 participants were exposed first to a WME task (T1) that required them to encode both the identity and the location of four symbols presented in a random order which was followed. After either a short delay SOA of 50-msec or a long delay SOA of 950-msec, the second task (T2) was presented.
T2 was a relatively simple task that required the participant to identify the presented letters (either H or S). It was proposed that participants would be more accurate and fast in their responses during long interval trials as they would have more resources available during these trials. In the second experiment, the processing load was reduced from WME. The 11 participants in this experiment only had to indicate whether the stimulus of T1 was presented, and the rest of the experiment was the same. It was believed that reducing the cognitive load would free attentional resources for T2.
The third experiment was similar to the first in most respects, except that the five participants included did not have to make a speeded response to T2. Results and Analyses The researcher found that WME did indeed influence the accuracy of responses to T2 in experiment one; and that there were distinct differences in the results of experiments one and two to favor accuracy and speed when T1 required fewer resources. Activation was observed in the visual cortex which correlated to the delay in processing T2 such that as the SOA increased, the errors and reaction time decreased.
It was observed that for about two seconds following the initial presentation, the BOLD signal in the visual cortex was slugging and provided a slow response, thus leading the researchers to conclude that even small differences in top-down activation can lead to larger differences in measures of activation like the BOLD signal. This could also account for the lack of difference seen among conditions in the second experiment. This experiment provided further evidence to support the study hypothesis.
The third experiment verified that the response for T2 did not cause visual cortex activation during the short SOA. Rather, delay in top-down attention to the visual cortex was implicated in both the delay and the errors. Conclusion The researcher concluded that the study hypothesis which states that WME heavy tasks cause a delay in top-down processing associated with the visual cortex was supported. There are some concerns about the small sample size, but taken alongside other research, these results present a compelling case.
WME seems to be associated with denying attention to distracters, and in levels of awareness. The researchers suggest that more detailed study of the mechanisms by which the WME functions is needed to understand its effect of different stimuli.