Tuesday, July 03, 2012

Adina Roskies on Libet's "Half Second Delay"

Sunset at Warren Dunes State Park, Michigan

Neuroscientist Benjamin Libet's experiments on consciousness in the 1970s claimed to show that there is an ever-so-slight temporal delay between the physical brain's being stimulated and the making of a conscious choice. See Libet et. al., "Subjective referral of the timing for a conscious sensory experience: a functional role for the somatosensory specific projection system in man." From the Abstract: "A temporal discrepancy between corresponding mental and physical events, i.e., between the timing of a subjective sensory experience and the time at which the state of 'neuronal adequacy' for giving rise to this experience is achieved, would introduce a novel experimentally-based feature into the concept of psychophysiological parallelism in the mind-brain relationship."

Libet wanted to find the cause of our spontaneous actions, like making a choice to do or not do something. If neural activity preceded and caused human choices, then it would seem that the idea of free will has been undermined. This is Libet's famous "half second delay." (Here's a nice little explanatory essay on this.) Libet did wonder, even if free will was an illusion, that perhaps we have "free won't"; viz., the ability to veto a decision the brain had already made.

But, according to Dartmouth neurophilosopher Adina Roskies Libet's work does not eliminate human free will. (Here's her audio presentation at Philosophy Bites. I just found this website this weekend - very cool.) Her reasons are:
  1. If you are a physicalist then it's not very surprising to find that the brain is doing something every time you make a decision. If consciousness is a process then there is going to be some extended brain event that underlies consciousness.
  2. You can't actually tell from Libet's experiment whether he is measuring a person's decision to, say (as in the experiment), move one's finger. There are other interpretations to what is going on; e.g., it could measure preparations to move one's finger, plans to do so, etc.
  3. "I don't believe [the Libet experiments] actually measure the time of conscious will. What they are measuring is the time at which you report being aware of having made a decision to move [one's finger]. What you're actually reporting is an awareness of an awareness to move. It's a meta-state; it's not the state you are interested in but a state about the stte you are interested in which is, a fortiori,  later than the state you are interested in."
 OK. But recent experiments using FMRI (functional MRI) have been reported to show that, 7-10 seconds before making a decision you are aware of making, that decision can be predicted. Roskies says that these studies only give a slightly better-than-chance prediction of a choice that will be made (55%). This "tells us nothing about whether or not we could do otherwise" (thus exercising free will).

Roskies is a compatibilist; viz., one who believes free will is compatible with physical determinism. She thinks we "can reconcile the notion of free will with the idea that we are mechanisms... There are a number of compatibilist theories out there that can explain how you can be a free even if you live in a deterministic universe."