Visual working memory (VWM) plays a pivotal role in our ability to process visual information. How is it instantiated in our brain?
Previous studies have demonstrated that there are several brainwave correlates of VWM. It’s great that we have many ways to observe VWM, but why do we have several but not one?
Well, there are two possibilities. One is that they are simply different measures of one thing. For instance, to measure how “big” a TV is, you can measure it by the length of the diagonal line, or you can calculate the surface area of it. Although these two measures are numerically different, they are correlated and they reflect the same physical property (i.e., size) that determines how “big” a TV is. Alternatively, different measures of VWM might indicate dissociable aspects of VWM. For example, to assess how “good” a TV is, one can assess its screen size and types of its input/output (e.g.,HDMI, DVI, etc). Unlike the measures of TV size, these factors reflect different aspects of TV quality, and therefore they are not necessarily related to one another.
Our recent work showed that two brainwave correlates of VWM are dissociable, and therefore, they are not a different reflections of the same aspect of VWM (Fukuda, Mance, & Vogel 2015; Fukuda, Kang, & Woodman, 2016). This suggests that VWM is not instantiated by a single neural process, but rather by multiple neural processes that are dissociable.
Okay,,, so what do the dissociable correlates of VWM reflect?
One of our recent work (Fukuda, Kang, & Woodman, 2016) showed that the dissociation has to do with the nature of VWM representation. One of the measures (the Contralateral Delay Activity, or the CDA) reflects lateralized VWM representations, and the other measure (Alpha power suppression) reflects spatially-global VWM representations. We are conducting more studies to characterize these dissociable measures of VWM more precisely, so stay tuned!