How Do Visual and Parietal Cortex Contribute to Visual Short-Term Memory?12

Visual short-term memory (VSTM) enables the representation and manipulation of information no longer present in the sensorium. VSTM storage has long been associated with sustained increases in univariate activity (eg, averaged single-neuron spike counts or fMRI activation levels) across a broad network of frontal and parietal cortical areas (for review, see D’Esposito and Postle, 2015). More recently, several research groups have used multivariate analytical techniques to “decode” or infer the identity of a remembered visual stimulus from multivariate fMRI responses measured in human visual cortical areas (eg, V1–V4) during the delay period of a VSTM task, even though these areas typically do not show sustained increases in activity during VSTM storage (Harrison and Tong, 2009; Serences et al., 2009; Riggall and Postle, 2012; Emrich et al., 2013; van Bergen et al., 2015). However, virtually all of these studies have used simple designs that require participants to remember information over a blank delay period. In many real world scenarios, information must be stored despite a constant barrage of dynamic and unpredictable sensory input. How does the brain accomplish this goal? A recent human neuroimaging paper by Bettencourt and Xu (2016) attempted to answer precisely this question. In their Experiment 1, participants were shown a sequence of two tilted gratings and retroactively cued to remember the orientation of either the first or the second grating. Following a blank delay period, participants judged whether the orientation of a probe grating was tilted slightly clockwise or anticlockwise of the remembered orientation. During the first half of experimental blocks, participants remembered the cued orientation over a blank delay (no-distractor blocks). During the second half of blocks, the delay period was filled with a sequence of …