psyc ppt v2
TRANSCRIPT
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Is Unconscious Movement Initiation an Artifact of the Clock?
Presenters: Pollyna. Shirley. Soon Hyung. Wai Chit. Wiharjo
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Electroencephalographic
What does this long word mean???
What is eeg?electroencephalographic
The recording of electrical activity alongthe scalp produced by the firing ofneurons within the brain
Recording of brains spontaneous
electrical activity Over a short period of time Recorded from multiple electrodes
http://upload.wikimedia.org/wikipedia/commons/7/7e/1st-eeg.png -
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WHO? Libet, Gleason, Wright, and Pearl
(1983)
WHAT? Recorded the electroencephalographic
(EEG) activity of people instructed togenerate occasional spontaneoushand movements.
HOW? Report the time of each spontaneous
decision to move by identifying thelocation at that time of a spottraveling around a clock display.
Brain Activity &consciousness
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RESULTS: Readiness potential (RP)
Began approximately 350 ms before the times at which people indicatedthey had decided to move
This pattern has been replicated several times
(e.g., Haggard & Eimer, 1999; Trevena & Miller, 2002).
SO? Results suggest that spontaneous decisions to move are initiated by the brain
before people are consciously aware of having made these decisions
Brain Activity &consciousness
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Negative-going shift in the EEG recorded atthe Cz electrode.
Logically impossible for negative shift toarise only in conjunction with movement
preparation.
Possibility of other brain processes?
Then its appearance before the consciousdecision to move DOES NOT truly support
the claim that movement preparationbegins unconsciously.
How reliableis the study?
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2 Experiments Jeff Miller, Peter Shepherdson and Judy Trevena
Negative shift is caused primarily (possibly exclusively)
The requirements to monitor the clock display
To report the spots position at the moment of thespontaneous decision to move.
Both time-monitoring processes + Movementpreparation
Possibility of inference ?
What should wedo then?
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IV: Time Monitoring
DV: negative shifts in EEG waves
Hypothesis: EEG waves are aresult of clock monitoring, not themaking of conscious decisions tomove.
Experiment 1
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Who were involved?
Participants
12 participants
- 8 Males, 4 Females
Students of University of Otago
Aged 19 30 (M=23.7)
Each session lasting 2.5 hr
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Responses recorded by IBMcomputer
Key-press responses made with
index finger of right hand on the Ikey
A spot indicated by a white crossmoved clockwise at constant 2.5sper circuit
Apparatus
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8 blocks of 20 trials (10 with clock, 10 w/o clock) Order of trials randomized In trials with clock, spot will move around the
clock perimeter starting from the top center Participants were told to relax, and generate
spontaneous key press. Told not to preplan but emit on an abrupt basis The moving spot will stop 500-800ms after the
key press response, after which the participantuse the left/right arrow key to reposition spot.
Procedures
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What are the findings?
Pre-movement negativity in EEGmay have resulted frommonitoring the clock rather than
from unconscious preparation formovement
EEG activity at start of trial wasalso affected by the clock,probably due to obvious visual
stimulation bet. clock andwithout clock
Miller J et al. Psychological Science 2010;22:103-109
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Who were involved?
Participants
12 right-handed volunteers
Aged 19 30
Did not do experiment 1
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Tones not obviouslyof different pitches
Volume forconversationalspeech
Experiment 2
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Accuracy > speech
Only informed whichkey to press aftersound was made
Experiment 2
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Presence of the clock had a significant impact on the EEG activity
Presence of a moderating variable
What are the findings?
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What are the findings?
Miller J et al. Psychological Science 2010;22:103-109
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Greater fluctuations in Cz amplitude with the presence of a clock
Clock monitoring affects the level of EEG activity
Rejects the hypothesis suggested in the previous study
Presence of the clock
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There was less EEG activity than there was in Experiment 1
Less brain activity required to listen out for tone(compared to choosing to move)
EEG activity from clock monitoring + EEG activity from task= Total EEG activity
Moderating variable:
The type of task
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Background Research
(Haggard & Eimer; Libet et al; Trevena & Miller)
Influence of the clock?
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Current Research
Challenge to the previous research
Experiment 1 Key-press movement
Negativity may result from monitoring clock
Experiment 2 tone for pitch judgment task
Moderating effect of the task
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Heisenberg Uncertainty Principle
The measurement process interferes with the
processes to be measured
Need more experiments