We investigated brain responses to matching versus nonmatching objects in working memory with a modified delayed match-to-sample task using event-related potentials (ERPs). In addition, ERP correlates of new items (new matches/new nonmatches) and previously studied items (studied matches/studied nonmatches) were examined in the working memory task. Half of the common visual objects were initially studied until 95% accuracy was attained and half were new. Each memory trial began with the presentation of a sample object followed by nine test objects. Participants indicated whether each test item was the same as the object held in mind (i.e., match) or a nonmatch. Compared to studied matches, new matches evoked activity that was 50 msec earlier and largest at frontal sites. In contrast, P3 activity associated with studied nonmatches was larger than for new nonmatches at mostly posterior sites, which parallels previously reported oldnew ERP effects. The ERP source analysis further confirms that the cortical mechanisms underlying matching objects and rejecting irrelevant objects during the task are both temporally and spatially distinct. Moreover, our current findings suggest that prior learning affects brain responses to matching visual items during a working memory task.
KeywordsERPs; visual memory; matching; delayed match-to-sample; stimulus evaluation; common objects; LORETA Intentionally holding an item in mind for current use is an important function of working memory (WM), an active, short-term memory mechanism (Baddeley, 1986;Baddeley & Hitch, 1974). Psychophysiological studies have localized several neural structures critical to WM including the prefrontal cortex implicated in coordination processes characteristic of the central executive (D'Esposito, 2001;Goldman-Rakic, 1996;Petrides, 1994;Postle 2006;Ranganath 2006;Wagner, 1999), posterior parietal cortex which participates in phonological coding and storage (Awh et al., 1996;Jonides et al., 1998;Postle & D'Esposito, 1999), thalamo-cortical activity which is implicated in allocating attentional resources towards a specific cortical region (Birbaumer, 1990;LaBerge, 1997), inferior temporal (IT) cortex that is involved in comparing current visual images with internal representations (Miller & Desimone, 1994;Vogels & Orban, 1994;Zhang et al., 1995), and the premotor areas that are Correspondence should be addressed to: Yang Jiang (yjiang@uky.edu), Department of Behavioral Science College of Medicine, University of Kentucky, Lexington, KY 40536-0086; Tel: 859-2572122, Fax: 859-3235350, or
NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript involved in the preparation of motor responses based on information held in mind (Petit et al., 1998).Many psychophysiological studies of working memory in primates and humans have used delayed match-to-sample tasks (Levy & Goldman-Rakic, 2000; Bichot, Rossi, & Desimone, 2005;Desimone 1996;Jiang et al., 2000). Typically, a sample item is presented at the beginning of the trial and after a de...