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what are executive control mechanisms?

Mind/brain has many specialised/domain-specific ‘modules’ available (for categorising, analysing/generating language, calculating, choosing actions, rehearsing, mental rotation etc)

control mechanisms must select and activate subset of processing ‘modules’ and organise, link and tune them to accomplish task


what processes don't happen from executive control mechanisms


All the time

Always in same way

Linked up in same way


selection/activation of single 'task-set'

Each object encountered affords many possible tasks

Task-set = appropriate organisation of perceptual, cog and motor resources to carry out task

To some extent select ‘at will’ which task-set to adopt according to current goals

To some extent env triggers familiar task-sets automatically (e.g. reading, recognising emotion, avoiding obstacles)


what are some other functions attributed to executive control?

Inhibiting inappropriate actions

‘Updating’: Selecting info for maintenance (/suppression) in WM

Managing search of LTM

Monitoring perf, troubleshooting, adjusting balance between accuracy and speed of perf

Coordinating aspects of multitasking, e.g. keeping diff info streams as segregated as pos, prioritising tasks

Sequencing, planning of multistep tasks esp. where actions required nonhabitual


what is the lure of the control homunculus?

i.e. attribution of control to unitary inner agent


examples of the lure of the control homunculus

Baddeley and Hitch (1974)

Norman and Shallice (1980/1986) - habitual/attractive/primed action/task-set wins unless SAS overrides

Gilbert and Burgess (2008)


how can we investigate control processes?

‘Natural history’ of control: Observation of:
- Failures of control in everyday life (some ‘action errors’
- Pathological failures of control after brain damage

Behavioural exps: Engage control processes in such as way that can isolate and study contribution to perf – in normal subjects/patients – e.g.:
- Exps on response conflict, e.g. Stroop effect
- Exps on task-switching
- Stop-signal exps
- Dual task and multitasking exps

And we can measure brain activity correlated with the exercise of control functions in these paradigms


what does systematic analysis of errors come from?

Diary studies

Accident enquiries


examples of types of control error

‘Capture’ errors – habitual/recently-exercised action patterns seize control of behaviour

‘Cross-talk’ errors – failure to keep separate elements of concurrent tasks, e.g.
- Picking up banana and holding it to ear instead of phone
- Concurrent writing and speaking (phonological code --> speech)

‘Lost intentions’: Failure to initiate intended action when ‘trigger conditions’ set in prospective memory occur


what happens with damage to the prefrontal cortex?

Imp of PFC for high level ‘organisation’ of behaviour suggested initially by clinical descriptions of patients with pre-frontal damage (Luria)

Neuropsych testing revealed several types control problems

Not always associated: Dissociations suggest fractionation of executive functions


examples of impairments due to PFC damage

‘Utilisation behaviour’
- Inability to suppress habitual action to familiar object

- E.g. Wisconsin card sorting test

Difficulty in evaluative decision making
- E.g. Damasio’s (1999) patient J (orbito-frontal PFC)

Disordered planning
- E.g. Strategy application disorder


what is the strategy application disorder?

Shallice and Burgess’s (1991) ‘multiple errands’ test (in shopping mall)
- Normal P’s path through mall
- P given money and instruction sheet: List of items to buy, info to find out, rendezvous and time, and some rules
- Perf of P with frontal lobe damage
- Disorganised perf:
- Subtasks not completed, ignored, repeated, done in inefficient order
- Rules broken
- Violations of social convention
- But not through lack of motivation


alternative explanations - no single executive 'homunculus'

Observed dissociations among impairments of exec control after brain damage argue against unitary ‘central exec’
- Instead, have distributed network of control mechanisms (in diff parts of PFC, basal ganglia and parietal cortex)
- Maintaining and controlling temp storage buffers small part of what exec control mechanisms do


how do we capture control in the lab?

Need to examine situs where need to:
- Suppress task-set/
- Reset control parameters/
- Inhibit actions, thoughts, memories, emotions/
- Manage multiple info flows

And try to isolate effects of demands on perf/brain activity from effects of task-specific process, arousal, emotion etc


what is the response conflict in Stroop's colour naming test?

Already have (in brains)
- Task-set for colour-naming
- Task-set for reading (much more practiced, habitual, ‘automatic’

Try to selectively attend to colour and apply naming task-set

But cannot (completely) suppress the reading task-set.

The difference in response time between the two conditions measures response conflict – which indexes the incompleteness of control.


what are some Stroop type inferences from habitual affordances?

Classic Stroop effect:
- RT (congruent) < RT (neutral) < RT (incongruent) - Green , ΔσφӨ , blue

How many digits
- 666 4444

Etc (See slides for more)


what is the Flanker effect response conflict triggered by application of instructed task set to irrelevant objects

5 letters will appear: Attend to central one: Press left key if S and right if H


comparing task switched and repeats in task-cueing exp

E.g. Monsell, Summer and Waters, 2003)

On each trial, coloured shape )(task cue) appeared, then digit in centre, P responds with left/right hand
- Pink background  odd/even
- Blue background  low/high

Task changed predictably every 4 trials – cue-stimulus interval varied


why is there a reduction in switch cost with prep?

Interval available for prep between response/cue and next stimulus 50, 650/1250 ms.response


what brain activity is associated with task-set reconfiguration?

Stimulus is word with letter coloured

Cue specifies task:
- Categorise word semantically (living/non-living)
- Decide whether colour pattern symmetrical


what is the neuroimaging response conflict and task-set prep?

MacDonald et al (2000)

Anterior cingulate cortex (ACC) activated more after incongruent than congruent stimuli: ‘Conflict detector’

Left lateral dorso-lateral prefrontal cortex (L.DLPFC) activated by prep for (harder) colour-naming more than by prep for word-naming: Task-set maintenance/suppression of stronger task set


what is the task-switch imaging 'task-set inertia' with fMRI

Stimulus = word on face

Classification tasks in runs of 4
- Word by no. syllables
- Face by gender

RT switch cost on first trial of run

In separate blocks ‘localiser’ tasks established word- and face- selective regions of activation (left Inferior Temporal Gyrus and right Fusiform Gyrus respectively)

Switch-trial-related activation of face-specific area predicts RT cost of switching to word task, and activation of word-specific area predicts RT cost of switching to face task


which processes are prolonged on task-switch trial?

Elchepp et al (2015) manipulated word freq: Effect shows up in ERP from 280ms

Onset of freq effect delayed on switch trials by substantial fraction of residual RT switch cost (50 +- 12ms)

Early processes prolonged on switch trials: Attentional inertia?


what is stop-signal RT?

a measure of response inhibition

Choice RT, but on some trials, a tone signals ‘don’t respond’

Vary stop-signal delay to find time required to inhibit response – stop-signal RT (SSRT)

In adults with ADHD, stopping impaired, but ‘go’ RT not

Stopping also abnormal in patients with OCD and Tourette’s