Psych 351B: Midterm 2 Review (Central Executive)

Central Executive

Involved in:

Executive attention

Switching executive attention from one activity to another

Ignoring/inhibiting information that has already been perceived

Scheduling a sequence of activities

Monitoring performance

Executive attention

Selective attention that acts on the contents of working memory and directs subsequent processing so as to achieve some goal

(goal directed attention with regard to working memory)

What can we say about the central executive

HINT: Is it a theory?

That it has to do with cognitive control, cannot treat it like a theory because it is simply a list of phenomena

Stroop test

One is shown a colour and a word and asked to either respond with the colour or the word (e.g. word is red and one must respond with either green or red depending on what is asked)

Stroop effect

The difference between the neutral and incongruent trials

T or F: those with frontal lobe damage (i.e. phineas gage) will do equally as well as controls when asked to name the word in the stroop test

T, test is asymmetrical, there is only an effect when naming the colour, not the word 

Describe the computational model that is used to explain the stroop test

There are 4 inputs for the stroop test, the two words and the two colours, activating one colour node will inhibit the other node and lead to a response (denoted using a barbell)

Why are some arrows thicker in the computational model

Because there is a stronger response for words than for colours

What is the problem with the computational model

Has nothing that allows for prefrontal control, therefore the word will always be selected due to its activation being stronger, thus we need some form of cognitive control

What is the reason for a hidden/intermediate layer in the model

Required so the model will work properly, allows the model to learn

How is cognitive control accomplished in the computational model

Reverberatory loop on goal information, has two parts:

Conflict monitor - tests if output is congruent with goal or not, if not attention controller is activated

Attention controller - connects back the colour nodes to increase activation

What is the problem found regarding brain activation during the stroop test using an fMRI

Expect that frontal lobe would be locally activated when engaged in cognitive control, in fact activation is scattered, not confined to any area

Why is the stroop effect so much smaller on congruent trials

Because one can respond incorrectly (read the word not the colour), but because the colour and the word are the same, their response is correct

Stimulus onset asynchrony

The interval between the onset of the word and the onset of the colour

What is found regarding task irrelevant/relevant dimensions depending on the polarity of SOA on a graph

If SOA is negative - task irrelevant dimension proceeds the relevant one

If SOA is positive - task relevant dimension proceeds the irrelevant one

Why can it be said that the stroop effect is asymmetrical

Words interfere with colour naming but colours do not interfere with word naming

Horse race theory of stroop results

Argues that there are two horses, one for words and one for colour. The word horse is much faster than the colour horse and that if they arrive at the same time then there will be conflict

According to the horse race theory why must words always be suppressed when trying to read colour

Because the word will always arrive to control first, thus if one wants to read colour they must suppress responding with the word

What is the problem with the horse race theory

Claims that if colour gets enough of a head start (about 10th of a second) then colour and word should arrive at the same time and thus conflict will arise when asked to read the word. This is not the case, as there is no interference

What do the fMRI results tell us with regard to the instructional phase of the stroop test

Anterior cingulate - there is no change regardless of goal (read colour or word)

Dorsolateral PFC - change that causes increased activation when asked to read colour

What do the fMRI results tell us with regard to the incompatible/compatible trials phase of the stroop test

Anterior cingulate - more active on incompatible trials then compatible trials

Dorsolateral PFC - No difference between incompatible and compatible trials, activation is equivalent

What do the fMRI results from the stroop test tell us with regard to the dorsolateral PFC and anterior cingulate

Anterior cingulate - engaged in dealing with conflict

Dorsolateral PFC - engaged in planning

Both work together and share the workload to complete tasks

Simon task

One is to respond with left sided keypress to a triangle and right sided keypress to a circle, the location of the shape is irrelevant

Simon effect

One will respond slower when shape and location are incompatible (e.g. triangle is on the right side of the screen), takes about 10 ms (compared to stroop effect 50ms)

Where does activation flow during the stroop test in the brain

Flows from the attentional PFC to the fusiform gyrus (for processing colour)

Where does activation flow during the simon task in the brain

Flows from the attentional PFC to the premotor cortex (this is much simpler as the premotor cortex can be activated without concious awareness)

Task Switching Experiment

Individual views two squares (cues) that are coloured and have a number inside of them (stimulus), blue means respond odd/even and red means respond above/below 5. Measure the RT of participants when the length of time between cue and stimulus presentation (either 50, 650 or 1250 ms)

What does it mean for the sequence to be predictable in the task switching experiment

Participant expects a pattern regarding the task they are told to engage in (e.g. 4 blue squares then 4 red squares, then 4 blues squares, etc.), forces one to cognitively switch between two tasks

What is found regard RT of participants relating to the number in the predictable sequence

One will respond much slower to the first term presented, the switch cost is very high, the other 3 terms are all pretty much equal to RT

Switch cost

The difference between the first and second stimuli RT, much lower depending on the length of the cue

Why is the RT so much higher on the first stimulus in the task switching experiment

Because one has not switched to the other task at the time of presentation and need to play “catch-up”

Residual switch cost

One can never fully prepare for an upcoming event which causes RT to be pretty much equivalent on the 650 and 1250 ms cues (1250 is actually slightly longer RT)

What are the two functions of the coloured square in the task switching experiment

1. Acts as a cue on which task to engage in (also when to switch between them)

2. Acts as a go/warning signal that tells one to be ready to act

How can readiness to act explain the greater RT of the 50 ms cue in the task switching experiment

One is not given enough time to prepare to act, thus leading to a slower response even knowing what the task is

How can readiness to act explain the greater RT of the 1250 ms cue compared to the 650 ms cue in the task switching experiment

Because one is unable to stay ready to act for the extra 600 ms they had to wait

Arrow Executive Attention Task

One is shown a cue, then an arrow pointing either left or right, asked to count how many arrows point right or left. The participant is given a button that allows them to advance to the next cue (and records how long it took for them to update count)

What is the switch cost of the arrow executive attention task

Very large, between 500 - 600 ms (know this is the switch cost as the difference is too large to be explained by anything else)

How can we get a dissociation between executive processes and task processes

By showing an experiment in which one condition can be satisfied without executive processes and the other relies on executive processes. We use the addition/subtraction experiment

Addition/subtraction Experiment

One is shown two numbers and told to either add or subtract them, has two conditions:

Pure - no switch required, one is to add the two numbers presented and then subtract all the numbers presented

Mixed - switching required, trial 1 is addition, trial 2 is subtraction

What must one use to respond to the pure condition

Can rely entirely on task processes, hence RT is shorter and completion is still easy even if symbols are removed

What must one use to respond to the mixed condition

Must rely on task processes and executive processes as they must be ready to swap conditions, hence RT is longer and completion becomes very difficult if symbols are removed

How can one make the pure condition more difficult, without needing to rely on executive processes

By reversing the letters or making them harder to see

T or F: The more similar the two tasks (rules for completion more similar), the greater the opportunity for confusion and thus we expect to see a larger switch cost

T, the reverse is also true

What is found regarding activation in the brain during the count (arrow) task and stimulus-response (simon) task using fMRI

Count - inferior parietal lobe and extrastriate visual-cortex both activated

Stimulus-response - anterior PFC and premotor cortex both activated

T or F: Switching executive attention is distinct from that of engaging executive attention

T, fMRI shows evidence for the role of parietal lobes in attention switching