Two dissociable updating processes in working memory
Each trial of the experiment presented a target set of consonant letters, followed by a delay period, followed by a probe letter (Fig.
1); subjects had to decide as quickly as possible whether the probe letter matched a letter in the target set.
The arrows along the time line represent the placement of independent variables positioned to detect variance in the f MRI signal associated with target presentation, delay period, and probe portions of the trial, respectively.
These findings characterize spatially and temporally a proactive interference effect that may reflect the operation of a PFC-mediated response-inhibition mechanism that contributes to working memory performance.Research on the prefrontal cortex (PFC) of monkeys and humans indicates that this region supports a heterogeneous repertoire of mental processes that contribute to many complex behaviors, such as working memory.Anatomical evidence for some of these processes derives from functional neuroimaging experiments using blocked experimental designs, which average signal across all components of many trials and therefore cannot dissociate distinct processes with different time courses.Results from two types of trials are detailed in this report: () Nonrecent Negative trials, in which the probe matched items from neither the current nor the two previous target sets.
We hypothesized that a correct response to a Recent Negative probe would engage interference resolution processes, possibly inhibition of the tendency to respond “yes” based on the sheer familiarity of the probe (which had been rehearsed extensively on the two previous trials).Subjects were excluded if they had any medical, neurological, or psychiatric illness or if they were taking any type of prescription medication. Subjects performed an item-recognition task during which they judged whether the probe was from the target set of four consonant letters (Fig. There were four trial types, each of which was defined by the probe: () a Nonrecent Positive probe matched an item that was presented in the current target set (and thus required a “yes” response) but not in the previous target set.