dual mechanisms of cognitive control todd braver cognitive control and psychopathology lab,...
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Dual mechanisms of cognitive control
Todd BraverCognitive Control and Psychopathology Lab,
Washington University
Plus:
Jeremy Reynolds
Josh Brown
Stefan van der Stigchel
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Cognitive Control
• What is cognitive control?– formation, maintenance and realization of internal goals– structuring thoughts and actions in accordance with these goals
• The problem: Interference– the environment often provides conflicting or distracting information– perceptually salient information or default action tendencies are often incongruent
with intended goals
– Examples: Action capture errors, RED
• A major function of control processes is to successfully manage interference
– What are the underlying neural & cognitive mechanisms?
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Dual mechanisms of control
• Our hypothesis => Dual mechanisms– Reactive control: Detection and resolution of interference– Proactive control: Anticipation and prevention of interference
• Reactive control– Transient, stimulus-driven activation of lateral prefrontal cortex (PFC) and other areas due to:
Spreading activation processes Detection of conflict (anterior cingulate cortex)
– Late correction mechanism: suppression of goal-irrelevant information when needed or just-in-time– Example: remember to stop at store after work (e.g. prospective memory); event-based triggering
• Proactive control:– Sustained active maintenance of goal-related information in lateral PFC
dependent upon phasic dopamine (DA) activity– Early selection mechanism: top-down attentional biases enhance access to goal-relevant information or
prepare appropriate actions– Example: Remembering your point in a conversation while others are speaking
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Why dual mechanisms?
• Cost-benefit analysis– Proactive control:
More effective, but More energetically demanding More vulnerable to disruption (precise DA dynamics required)
– Reactive control More susceptible to interference effects (late correction), but Less demanding, more robust
• A mixture model– Both control strategies are used but weightings can differ:
Across task situations: Opportunity & Impact Across individuals: May be dependent upon biases and capabilities
– May even be trial-to-trial variability (e.g,. natural fluctuations) Task-switching
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Research Strategy
• A cognitive neuroscience approach– Cognitive Experiments: Manipulation of control strategy, look for behavioral
markers– Brain Imaging: Dynamics of activity in lateral PFC, ACC, other regions– Special populations: Effects due to normal individual differences
(personality, intelligence), impaired functions (older adults, schizophrenia)– Computational Modeling: Mechanistic explanations, bridging brain &
behavior
• Domains– Working memory (e.g., Sternberg task)– Controlled attention (e.g., Stroop)– Task-switching
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Task-switching
• Key Issues– Switch costs imply interference from other task sets– Preparatory interval effects on switch cost implies proactive control is being used (Meiran)
Task-set (goals) are actively maintained and used to bias attention– Residual switch costs with long preparatory intervals suggest this can’t be full account
• Accounts– Task-set inertia (Allport): Emphasis on unresolved interference rather than proactive control– Exogenous cuing (Monsell): Proactive control is incomplete until target presented– Failure-to-engage (DeJong): Probabilistic proactive control; intermittent failures
• Problem– If no proactive control, how come interference effects are not catastrophic?– Ambiguous targets (bivalent, incongruent) can only be performed appropriately if task-set
information is accesssible (e.g., actively maintained)
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Our hypothesis
• Prepared trials = proactive control– Actively maintained PFC representations lead to preparatory biasing prior to target
stimuli– Updating and maintenance in PFC triggered by phasic dopamine burst occurring
during task cue presentation
• Unprepared trials = reactive control– Transient activation of PFC during cue presentation, but no updating and
maintenance Dopamine system is noisy; no phasic response on some trials
– Target-driven reactivation of cue leads to late biasing of relevant task pathways
• Goal– Develop computational model to demonstrate mechanisms– Demonstrate that model can capture task-switching behavioral phenomena
Switch costs, congruency costs, etc. De Jong mixture analysis: prepared (fast) trials show no switch costs,
unprepared (slow) trials show maximal switch costs– Demonstrate that model can capture task-switching brain activity dynamics
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Experimental Paradigm
• Unpredictable (trial-by-trial) cueing, letter-digit task– Long preparatory interval (1500 msec)
ConsVowel
TASK A
Odd Even
TASK B
LETTER
X 9
Time TimeNUMBER
X 9
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Neural network model
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Simulations
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Proactive control (prepared) Reactive control (unprepared)
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Simulation Mechanisms
• DA-based updating is probabilistic (50% of trials)– Results in mixture of unprepared and prepared trials– DA gating enables active maintenance
• Co-Activation leads to associative (Hebbian) strengthening (priming)
• Prepared trials (proactive control)– Task set information is actively maintained during preparatory interval (in PFC module)– Biases appropriate task-pathway– Local competition leads to suppression of irrelevant task set and pathway– Reduced interference effects (e.g., switch costs)
• Unprepared trials (reactive control)– Task-set information transiently activated with cue, leads to associative strengthening
(priming) with task pathway– Task-set decays during preparatory interval– Target presentation causes reactivation of appropriate task-set– Task-set interference is greater on switch trials and incongruent trials– Increased interference effects (congruency & switch costs)
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Error Rate Data
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RT data
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RT distribution data
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Mixture Analysis
Nonswitch(plus switch -gating) Switch-no gating
Switch-all trials
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Preparation & Errors
Unprepared Prepared
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Simulated PFC Activity
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Actual PFC ActivityBraver, Reynolds, and Donaldson (2003) Neuron
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Summary
• Task-switching effects might reflect dual mechanisms of cognitive control– Proactive control: Active maintenance of task-set and preparatory biasing– Reactive control: Reactivation of task-set following target
• This theory provides resolution of key questions– Residual switch costs due to probabilistic preparation– Performance on non-prepared trials aided by reactive control– Task-set interference only present on unprepared trials– PFC activity associated with task-cues may be variable
• Framework may account for other issues as well – Mixing costs: Anterior vs. dorsolateral PFC; proactive biasing of eligible tasks– Sequential effects: Conflict (Incongruency)-based strengthening of active task (e.g. Goschke,
2000)– Asymmetric switch costs: no repetition benefits for weaker task w/o proactive control– Other domains: WM, selective attention, individual differences
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Future Directions
• Asymmetric Switch Costs (van der Stigchel)
• Mixing Costs (Neuron)
• Conflict Effects (Brown)