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Experimental design

- Summary methods of Matsuhashi & Hallett (2008) - proposed experimental design Experiment 1
by

Ceci Verbaarschot

on 30 June 2013

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Transcript of Experimental design

Questions?
Matsuhashi & Hallett (2008)
Experimental design
Motivation
General experimental design
Detailed experimental design
Experimental design
Results
Analysis
Concerns Libet et al. (1983):
relies completely on subjective recall
reading and memorizing clock position causes additional preparation and latency times
experimental paradigm might have altered mental process of voluntary behavior into a reaction triggered by the feeling of intention

--> new method to get real-time decision intention onset
Intention = specific thought that you will be making a movement

Movement genesis = brain process of making movement

16 right handed subjects participated in the experiment
T: -1.42s and 0.69s

P: -0.13s and 0.07s

BP1: -2.17s and 0.69s

BP2: -0.57s and 0.20s

LRP: -0.59s and 0.28s
RT-task

tones were applied at pseudo-random intervals of 2-10s
subjects performed brisk right finger extensions as quickly as possibly each time they heard a tone
Veto-task

subjects performed self-paced right index finger extensions at intervals of 5-10s as soon as the thought of movement came to mind
tones were applied pseudo-randomly at intervals of 3-20s
ignore the tone when they were not thinking about the next movement and continue their self-paced movement
veto the movement in progress after hearing the tone when they started thinking about the next movement and wait another 5-10s interval before the next movement
tones that came after a movement were ignored
Movement onsets were marked manually at the beginning of the EMG burst

The timing of tone onset relative to movement onset was accumulated across all marked movements

If a subject completely ignored the randomly presented tone, the distribution should be uniform before movement onset

However, tones that happened in a certain period before movement onset would cause cancellation of the following movement and would not contribute to the constructed tone distribution, making a dip in this otherwise uniform distribution
Time of thought to act (T) and point of no return (P) were estimated from the shape of this distribution using two methods:

Sigmoid curve fitting
Density estimation
RP analysis:

data were averaged with an analysis window of 2.5s prior to movement onset to 0.5s after movement onset
the first 0.5s of the window was used as a baseline
onset latencies were measured at C3 and Cz separately and then averaged
Feedback?
Ideas?
Equipment:
1x Biosemi Active-2 256 channel EEG AMP
1x 64 electrode 10-20 system cap (M size)
1x monitor for displaying the stimuli
2x button box
2x speaker
4x bipolar electrodes to record EMG of right and left forearm
4x bipolar electrodes to record EOG of left eye
Measure muscle activity of both left and right arm using EMG:
2 bipolar electrodes just below the elbow on both right and left forearm to record the activity of the arm muscles moving both right and left index fingers during a button press
another 2 electrodes on the wrist bone of both the right and left wrist
record the EMG for each arm as the difference between the electrode on the wrist bone and the forearm
use recorded EMG activity to check the accuracy of the timing of the recorded button presses during off-line analysis
Veto-task:
subject will be watching slides on computer screen
slides consist of landscape images
subject can press a left button with their left index finger or a right button with their right index finger to go to the next slide
both actions will trigger a new slide

A single tone will be presented randomly on each trial

Subject is instructed to:
ignore the tone when they were not thinking about the next movement, keep performing self paced act
veto next movement if they were thinking about the next movement when they heard the tone, wait for next trial
Preparation phase:
cap fitting, providing instructions, etc.
approx. 30min.

Training phase:
familiarize experimental setup
10 RT trials + 10 Veto trials
approx. 3.5min.
Record eye blinks and movements using EOG:
2 bipolar electrodes just above and below the left eye to record blinks and vertical eye movements
another 2 electrodes to the outer sides of both left and right eye to record horizontal eye movements
Subject is instructed to wait a while (about 3 seconds) at the start of each trial before making or preparing any movements (used as a baseline)
Random trial length (between 13 and 33 seconds)
If subject does not perform action during that time, automatically go to next trial
ask subjects if they were aware of next action when they heard the tone (double check)
If subject does perform action during that time, next trial is triggered
RT-task:
a single tone will be presented randomly on each trial
L or R on screen indicates which button to press
subject is asked to press button as quickly as possible after hearing a tone
max trial length 5s

Purpose: measure RT between awareness of tone and button press
Testing phase:
data collection
60 RT-trials + 200 Veto-trials
in between blocks there is a break, subjects can resume experiment at their own pace
approx. 54min.
Total duration: 1.5hours
Veto-trials:
semi-random trial length
purpose: enhance feeling of free choice
80% trials <= 13s
10% trials > 13s & <= 23s
10% trials > 23s & <= 33s
Goal
RP does not reflect movement preparation
(Schurger, Sitt, Dahaene (2012))
Use individual RP vs. intention model to present informed probes using an online BCI
Full transcript