Task switching is not a unitary phenomenon: Behavioral and neuroimaging evidence

1. Task switching is not a unitary phenomenon: Behavioral and neuroimaging evidence S.M. Ravizza1& C.S. Carter1,2 Depts. of 1Psychology & 2Psychiatry, University of California, Davis, Imaging Research Center D I S C U S S I O N I M A G I N G M E T H O D S M E T H O D S R E S U L T S Shift Cost Stimulus Repetitions • Shift cost was greater in the perceptual condition • One difference between the two conditions is that the irrelevant dimension is present in the perceptual condition • However, shift cost is absent without the presentation of the irrelevant dimension in the perceptual condition (-4 ms vs 384 ms). • Therefore, shift costs in the perceptual condition seem to be driven by interference from the irrelevant dimension at the time of presentation • Stimulus repetition benefits were greater in the contextual condition • This may be because targets were always associated with the same response in the contextual but not the perceptual condition X S T S S T T X R E S U L T S R E S U L T S DLPFC is greater for shifts of context than perceptual shifts Parietal regions are more active for perceptual switches than contextual D I S C U S S I O N Contextual and perceptual shifts of attention invoke differences in behavior and neural engagement. Stimulus repetitions are a bigger component of the shift cost in the contextual condition whereas stimulus interference primarily drives shift cost in the perceptual condition. The DLPFC, a region associated with the maintenance and updating of context, was important when the relevance of S-R mappings switched Parietal, occipital, and cerebellar regions were most important for shifts between relevant features of a stimulus These results indicate that task switching is a complex form of cognitive control that is instantiated by different neural regions depending on the type of switch required B118 I NT RODUCT I ON • Task switching has been operationalized in a variety of ways across studies • No studies have been run assessing whether behavioral effects vary according to the type of switch required • Only recently have attempts been made to dissociate neural activity in regard to different types of shifts (Wager, et al., 2005). • We focus on two types of shifts: • Perceptual shifts – shifts between the processing of stimulus features such as color and shape • Contextual shifts – shifts in the rules or relevant information needed to perform tasks Question 1: Will behavioral effects differ depending on the type of shift performed? Question 2: Will neural regions be more important for one type of shift than the other? Subjects Six undergraduates participated (avg. age = 28) Stimuli + 2000ms + 500ms 2000ms Left Angular Gyrus (-43,-72,7) 13500ms Shift cost is greater for perceptual switches (shift x task: F (1,9) = 7.6, p < .05) Procedure & Analyses • 7 – 9 runs of 24 trials each were obtained for each participant. • One block of each condition was presented in each run, and the starting condition was random between runs. • Only the 2nd trial of each pair was analyzed • ROIs were obtained using a shift (2) x task (2) x time (7) ANOVA. • Voxel-wise tests used a threshold of p < .001 and a cluster size of 4 voxels Right Superior Parietal (-43,-72,7) Other regions showing this pattern are the right cuneus (BA 18) and cerebellar vermis Subjects Ten undergraduates participated Stimulus repetition priming is greater for perceptual switches (F (1,9) = 8.52, p < .05) Stimuli Procedure The task in both conditions is to find the odd target. In the perceptual condition, participants responded to the target’s location whereas, in the contextual condition, participants responded to the key memorized to the target identity in a previous practice block. Perceptual and contextual switches were blocked and there were 256 trials in each condition. Stimuli stayed on the screen until a response was made and the response-to-stimulus interval was 500 ms. Left DLPFC (-42,40,28) This is not due to greater difficulty with switching as shift cost in the contextual condition was less than the perceptual (65 ms vs 212)