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
B118

• 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?

I NT RODUCT I ON
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 lt .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 lt .001
  and a cluster size of 4 voxels

Right Superior Parietal (-43,-72,7)
Type EPI Slices 36
Scanner 3T Siemens Trio TR 2000 ms
Voxel size 3.438 x 3.438 x 3.4mm TE 25 ms
Flip angle 90 FOV 220 mm
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 lt .05)
Stimuli
Procedure The task in both conditions is to find
the odd target. In the perceptual condition,
participants responded to the targets 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)