Task switching is not a unitary phenomenon: Behavioral and neuroimaging evidence S.M. Ravizza 1 &...
1
Task switching is not a unitary phenomenon: Behavioral and neuroimaging evidence S.M. Ravizza 1 & C.S. Carter 1,2 Depts. of 1 Psychology & 2 Psychiatry, University of California, Davis, Imaging Research Center 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 Perceptual shifts – shifts between the processing of stimulus features such as color and shape Contextual shifts 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 I N N T T R R O O D D U U C C T T I I O O N N M M E E T T H H O O D D S S 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 D D I I S S C C U U S S S S I I O O N N Shift Cost Stimulus Repetitions R R E E S S U U L L T T S S I I M M A A G G I I N N G G M M E E T T H H O O D D S S B118 Type EPI Slic es 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 DLPFC is greater for shifts of context than perceptual shifts R R E E S S U U L L T T S S Left DLPFC (-42,40,28) Parietal regions are more active for perceptual switches than contextual R R E E S S U U L L T T S S Left Angular Gyrus (-43,-72,7) Subjects Subjects Ten undergraduates participated Percep tua l sw itches Percep tua l sw itches C ontextua l sw itches C ontextua l sw itches Repeat Repeat Switch Switch s t t t s s x s s t x o n b b b n n v n Stimuli Stimuli Procedure 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. 0 200 400 600 800 1000 1200 1400 1600 1800 2000 C ontextual Perceptual RT shift repeat 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Contextual Perceptual RT repeat reverse Shift cost is greater for perceptual switches (shift x task: F (1,9) = 7.6, p < .05) Stimulus repetition priming is greater for perceptual switches (F (1,9) = 8.52, p < .05) 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 D D I I S S C C U U S S S S I I O O N N Subjects Subjects Six undergraduates participated (avg. age = 28) Procedure & Analyses 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 Stimuli Stimuli 500ms 2000ms + S S S X 2000ms + X T T T 13500ms -0.3 -0.2 -0.1 0 0.1 0.2 0.3 2 3 4 5 6 7 8 9 PercentC hange C ontextrepeat C ontextshift Spatialrepeat Spatialshift -0.4 -0.2 0 0.2 0.4 0.6 2 3 4 5 6 7 8 9 PercentC hange C ontextrepeat C ontextshift Spatialrepeat Spatialshift -0.2 0 0.2 0.4 0.6 0.8 1 2 3 4 5 6 7 8 9 PercentC hange C ontextrepeat C ontextshift Spatialrepeat Spatialshift Right Superior Parietal (-43,-72,7) Other regions showing this pattern are the right cuneus (BA 18) and cerebellar vermis This is not due to greater difficulty This is not due to greater difficulty with switching as shift cost in the with switching as shift cost in the contextual condition was less than the contextual condition was less than the perceptual (65 ms vs 212) perceptual (65 ms vs 212)
-
date post
21-Dec-2015 -
Category
Documents
-
view
215 -
download
0
Transcript of Task switching is not a unitary phenomenon: Behavioral and neuroimaging evidence S.M. Ravizza 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 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 shiftsPerceptual shifts – shifts between the processing of stimulus features such as color and shape Contextual shiftsContextual 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?
IINNTTRROODDUUCCTTIIOONN
MMEETTHHOODDSS
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 switchedParietal, occipital, and cerebellar regions were most important for shifts between relevant features of a stimulusThese 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
DDIISSCCUUSSSSIIOONN
Shift Cost
Stimulus Repetitions
RREESSUULLTTSS
I I MMAAGGIINNG G
MMEETTHHOODDSS
B118
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
DLPFC is greater for shifts of context than perceptual shifts
RREESSUULLTTSS Left DLPFC (-42,40,28)
Parietal regions are more active for perceptual switches than contextual
RREESSUULLTTSS
Left Angular Gyrus (-43,-72,7)
SubjectsSubjectsTen undergraduates participated
Perceptual switchesPerceptual switches Contextual switchesContextual switches
RepeatRepeat
SwitchSwitch
s t t t
s s x s
s t x o
n b b b
n n v n
StimuliStimuli
ProcedureProcedureThe 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.
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Contextual Perceptual
RT shift
repeat
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Contextual Perceptual
RT repeat
reverse
Shift cost is greater for perceptual switches (shift x task: F (1,9) = 7.6, p < .05)
Stimulus repetition priming is greater for perceptual switches (F (1,9) = 8.52, p < .05)
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
DDIISSCCUUSSSSIIOONN
SubjectsSubjectsSix undergraduates participated (avg. age = 28)
Procedure & AnalysesProcedure & Analyses7 – 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 analyzedROIs 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
StimuliStimuli
500ms
2000ms+
SS S X
2000ms+
XT T T
13500ms
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
2 3 4 5 6 7 8 9
Per
cen
t C
han
ge
Context repeat
Context shift
Spatial repeat
Spatial shift
-0.4
-0.2
0
0.2
0.4
0.6
2 3 4 5 6 7 8 9
Per
cen
t C
han
ge
Context repeat
Context shift
Spatial repeat
Spatial shift
-0.2
0
0.2
0.4
0.6
0.8
1
2 3 4 5 6 7 8 9
Per
cen
t C
han
ge
Context repeat
Context shift
Spatial repeat
Spatial shift
Right Superior Parietal (-43,-72,7)
Other regions showing this pattern are the right cuneus (BA 18) and cerebellar vermis
This is not due to greater difficulty with This is not due to greater difficulty with switching as shift cost in the contextual switching as shift cost in the contextual condition was less than the perceptual (65 condition was less than the perceptual (65 ms vs 212)ms vs 212)
