Task 9- Consciousness Flashcards
What is a readiness potential (RP)?
slow negative shift in electrical potential generated by the brain (SMA), beginning up to a second before a self-paced, apparently voluntary motor act
What is RP 1? And when does that occur?
- only in trials where subjects reported planning/preparation to act
- Ramp-like RP with an average onset at about 1050ms before motor act
What is RP 2? When does that occur?
- the one uniquely associated with an exclusively endogenous volitional process/ spontaneuos
- Average onset at about 550ms before motor act
How is voluntary action and will characterized?
- Arises endogenously
- No externally imposed restrictions/compulsions that controls one’s initiation and performance of the act
- One feels introspectively that they are performing the act voluntarily and that they are free to (not) start the act as they wish
What were the instructions in Libet’s study?
-Perform a prescribed motor act (flexing finger) at some time (free to choose) after the start of each trial
-Pay close introspective attention to the onset of the urge to perform the act
*W – experience of the first awareness of wanting to move
*Indication of the timing: there was a light spot going around a clock face and participants later had to say on what number it was when the urge occurred
-Should not plan the act, should be “spontaneous”
How did Libet check for the validity of W(=experience of first awareness to move)?
–> Second Experiment with S
- skin stimulus was delivered at an irregular, randomized time after the start of each trial -> subject reported the time of his awareness of the stimulus
- discrepancy between the subject’s reported timing and the actual stimulus time could be objectively determined
- S were usually reported to occur a little in advance of the actual delivery time
- -> W-S: -150 MS (so W 50 MS later than first thought)
Which kinds of measurements were compared to each other in Libet’s study?
- compare time of onset of the conscious intention to act (W) and the time of onset of associated cerebral processes (RP)
- compare W and the actual time of the voluntary motor act (indicated EMG)
What were the results of Libet’s study?
-When took W and RP place physiologically?
-“physical” (= cerebral process, RP) precedes the “mental” (= conscious intention, W)
*W = on average 200ms before muscle activation
-RP 1= 1050 before motor act
-RP 2= 550 ms before motor act -> consistently in advance of W
-PMP (premotor potential): 50 MS before
-Reported times for W were the same for RP 1 and 2
What are the conclusions drawn from Libet’s study?
-What are voluntary acts initiated by?
- Voluntary acts can be initiated by unconscious cerebral processes BEFORE conscious intention appears
- -> Brain decides to initiate or at least prepare the act before there is any reportable subjective awareness of the decision
What are the conclusions drawn from Libet’s study concerning conscious control?
- conscious control over the actual motor performance of the acts remains possible
- Conscious volitional control may operate not to initiate the volitional process, but to select and control it
- -> Either by triggering the final motor outcome or by vetoing the progression to actual motor activation
What is free will according to Libet’s study?
Free will is restricted/ different to what we would think -> selects voluntary outcomes rather than initiate them
Conscious volitional control in Libet’s study
- When is MP generated?
- Could conscious control block the onset of MP?
- Motor potential (MP) is generated at about 50ms before muscle EMG
- So there remains a period of about 100-200ms (btw W and MP) in which conscious control could block the onset of the MP
How did Libet find evidence for veto?
- Subjects reported that during some of the trials a recallable conscious urge to act appeared but was suppressed before the actual movement occurred
- subjects were asked to develop an intention to act and to veto about 100 to 200ms before the prearranged clock time
- Pre-event potential was still recorded before the prearranged time, even though no muscle activation occurred
- -> Preparatory cerebral processes associated with an RP can and do develop even when intended motor action is vetoed at approx. the time that conscious intention would normally appear before a voluntary act
What did Soon want to investigate?
Directly investigate which regions of the brain predetermine conscious intentions and the time at which they start shaping the motor decision
How did Soon set up his experiment?
- Freely paced motor-decision task
- Fixate on centre of screen where a stream of letters was presented
- At some point chose to press one of two buttons (left/right)
- In parallel they should remember the present letter
- After a response mapping screen appears: second button press to choose the letter
- Pattern-based decoders were trained to predict the specific outcome of a subject’s motor intention by recognising characteristic local brain patterns associated with each choice (fMRI)