[Eeglablist] Meta-analysis on Libety-style experiments: Call for unpublished data

Moritz Braun moritz.braun at uni-saarland.de
Thu Nov 7 05:47:28 PST 2019


Dear colleagues,

In 1983, Benjamin Libet and colleagues published an influential study that sparked discussion and research on the existence of free will (Libet, Gleason, Wright, & Pearl, 1983). Studies in this tradition investigate the temporal pattern underlying the decision when to perform a volitional movement. Our research team at Saarland University is currently conducting a meta-analysis on Libet-style experiments, by which we mean experiments that are in a broader sense conducted in the “Libet-tradition”. For more information on the meta-analysis, see the abstract at the end of this email.

We are looking for unpublished data of studies in which healthy participants performed a task in which they had to choose the time for performing one specific motor action (so-called “when-task”). We are looking for studies that measured at least one of the following times, using any time measurement (e.g., Libet clock method, letter stream, inner monologue) and any monitoring technique (e.g., EEG, MEG, fMRI, none):

1) The time difference between the conscious intention to act and the actual onset of the movement (often referred to as “W-time”)

2) The time difference between the subjective awareness of the onset of the movement and the actual onset of the movement (often referred to as “M-time”)

3) The time difference between the onset of cerebral activity and the conscious intention to act (i.e. the onset of a neuronal marker minus W-time)

4) The time difference between the conscious intention to act and the	 subjective awareness of the onset of the movement (i.e. W-time minus M-time)

If you have any data concerning one or more of these times, we would appreciate if you shared your data with us. There are several ways to do so.

You can send us the raw data of your study in .csv format or as a file of any common statistics program (R, SPSS, SAS, Stata).

For your convenience, you can also use the following online sheet to enter the necessary data: 

https://www.soscisurvey.de/meta_analysis_libet/

Alternatively, you can send us an output file of a statistics program of your choice (ideally as pdf) with the necessary information. See the end of this email for an overview.


We are aware that responding to this request requires effort. Nonetheless, we hope that you can find some time to help us out. The more data we can include, the more conclusive the meta-analysis will be. 

Please send us the relevant data until the 8th of December 2019 and please do not hesitate to contact us if you have any questions! 

Thank you for your help! It is greatly appreciated.

Kind regards, 

Moritz Braun, Janet Wessler, & Malte Friese

Department of Psychology, Saarland University, Germany



*** Additional information about the meta-analysis ***


Abstract

Free will and the ability to intentionally and willingly act are two of the core properties human beings ascribe to themselves. In the light of the modern neuroscientific debate, these concepts are, nonetheless, often questioned. In the seminal Libet experiment (Libet, Gleason, Wright, & Pearl, 1983) on self-paced motor actions, preparatory brain activity preceded the conscious intention to act by about 350ms which again preceded the subjective awareness of the onset of the movement by another 150ms. These results sparked debates in various disciplines like philosophy, neuroscience and psychology, because some researchers interpreted these results to suggest that free will is a mere illusion. At the core of the debate and the research literature is the temporal pattern of preparatory brain activity, the conscious intention to act, the subjective awareness of the onset of the action and the actual onset of the action. The present meta-analysis aims at quantifying the average effect sizes of the main time differences based on all available evidence with meta-analytic techniques. We will further examine potential moderating factors of these time differences.



List of requested information provided in a pdf output of any statistics software: 

- Mean and standard deviation of those of the times 1) – 4) you conducted 
- The associated test statistics (e.g., t-value, F-value)
- The number of healthy participants investigated
- The number of trials per time per participant 
- The number of training trials per time per participant
- The number of regular sessions per time per participant
- The movement that was to be performed 
- The neural marker used (e.g., readiness-potential (please state if you used the RP1 or the RP2, see Libet et al. 1983) or lateralized readiness-potential)
- The exact instructions you gave to the participants regarding the reports of each time (including the mode of reports, e.g., point to, verbal, mouse click)
- The monitoring instrument you used (e.g. EEG, MEG, fMRI, none) and if you used an EMG to determine the actual onset of the movement 
- The time measurement you used (e.g., Libet clock method, stream of letters, inner monologue)
- If you used the Libet clock method as the time measurement: the mode of recall (absolute or order mode of recall; see the end of this email for a description of the modes of recall)
- If you used any control for subjective response biases: which?
- If the participants knew that the study focused on free will
- If there was any experimental manipulation (e.g., text about free will handed to the participants, TMS, sham TMS)
- In case you used time reports of the onset of externally induced sensory stimuli with or without feedback given to the participants concerning the accuracy of these reports as a control for subjective response biases (often referred to as “S-trials”): Mean, standard deviation, the number of healthy participants you investigated, the number of trials per participant, the number of training trials per participant, the number of regular sessions per participant, the associated test-statistics, the monitoring instrument you used (e.g., EEG, MEG, fMRI, none), the time measurement you used (e.g., Libet clock method, stream of letters) the stimulus modality (e.g., tactile, auditory, visual) you used in these trials, if you gave feedback to the participants concerning the accuracy of their reports and the exact instructions you gave to the participants (word-for-word; including the mode of the report, e.g.; point to, verbal, mouse click).



Absolute and Order mode of recall (Libet clock method)

Absolute mode of recall: Participants report the position of the clock hand (at the time of their conscious intention to act or the time of their subjective awareness of the onset of the action) after they performed the action.

Order mode of recall: The clock hand stops at a random point on the clock face after the performance of the action. Participants then report whether the final stop position of the clock hand was earlier then, later then, or at the same position as the clock hand was at the time of their conscious intention to act, or the time of their subjective awareness of the onset of the action.  









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