Poster C38, Sunday, March 25, 1:00-3:00 pm, Exhibit Hall C
The influence of storage capacity versus control in visual working memory capacity limitations
Ying Cai1,2, Andrew D Sheldon3, Bradley R Postle2,4; 1National Key Laboratory of Cognitive Neuroscience and Learning, Beijing Normal University, 2Department of Psychiatry, University of Wisconsin–Madison, 3Medical Scientist Training Program and Neuroscience Training Program, University of Wisconsin–Madison, 4Department of Psychology, University of Wisconsin–Madison
Many studies of visual working memory (VWM) capacity confound the constructs of "storage capacity," "context binding," and “inter-item interference.” During fMRI of a delayed-estimation task (n=16), we dissociated the experimental factor of load -- one bar that could vary in orientation ("1O") vs. three differently oriented bars ("3O") – from that of category homogeneity -- 3O vs. one bar, one patch that could vary in chrominance, and one concentric-circle stimulus that could vary in luminance contrast ("1O1C1L"). Fitting behavioral data to a 3-factor mixture model revealed no difference in memory precision between 1O and 1O1C1L conditions, but significantly worse precision for 3O. Subjects with higher VWM capacity, estimated offline with color change-detection, had a smaller decline in precision of 3O relative to 1O1C1L. Probability of target responses was highest for 1O, followed by 1O1C1L, followed by 3O. Delay-period BOLD signal in parietal and frontal areas was comparable in 1O and 1O1C1L conditions, and higher for 3O. Orientation reconstruction with multivariate inverted encoding modeling (IEM) of this delay-period signal was only successful for 1O trials, a pattern most consistent with a context binding function. IEM of encoding-related signal in occipital cortex, in contrast, produced successful orientation reconstruction for 1O and 1O1C1L, but not for 3O. Furthermore, dividing subjects into homogeneity-sensitive versus homogeneity-insensitive groups (based on the behavioral measures) indicated that the 1O1C1L-3O reconstruction difference was most pronounced in the homogeneity-sensitive group, a pattern most consistent with an inter-item interference. Fronto-parietal VWM activity reflects control, an important determinant of VWM capacity.
Topic Area: EXECUTIVE PROCESSES: Working memory