John Ostrowick, School of Computer Science, University of the Witwatersrand, Johannesburg, South Africa.

Transcription

1 John Ostrowick, School of Computer Science, University of the Witwatersrand, Johannesburg, South Africa. Paper at: 1

2 Abstract Benjamin Libet (1985) has provided neurological evidence that agents lack free-will except under special circumstances where the agent in question changes her mind. This paper discusses Libet s interpretation that the ability to change ones mind indicates that free-will may yet be possible and the conclusion is drawn that it may be inconsistent for Libet to do so, because it does seem as if he has provided strong evidence against the reality of free-will. Further evidence and criticisms of Libet s work is discussed, and these objections are dealt with. 2

3 The experiments Libet: Timed wrist-flexing act (A), RP ( readiness potential brain voltage change before action), motor cortex signal (M), and feeling as of wanting to act (W) compared to moving spot on a CRT. Control stimulus S on the skin was used to ensure accuracy of timing of W. Also measured V (veto, change of mind) timing. Grey Walter: Wired RP-detecting electrodes to slide changer, gave subjects dummy slide button. No control stimulus. Slide changed when RP initiated. (We mention this experiment because it corroborates Libet s results). 3

4 The results Libet: A occurred at 0.0 sec. M occurred at approx sec. W occurred at approx -0.2 sec. RP occurred at approx sec. V occurred at sec. He concluded that RP caused actions, not W (wanting to perform the action). The only room for free-will is V. It was concluded that cerebral initiation of a spontaneous voluntary act begins unconsciously. However, it was found that the final decision to act could still be consciously controlled during the 150 ms or so remaining after the specific conscious intention appears. (1985, p529) 4

5 The results Grey Walter: Subjects reported that slide show device had a bizarre precognition; it read their minds and changed the slide before they had decided to change the slide. Näätänen: Similar experiment, confirmed Libet s results, even for spontaneous unplanned actions. 5

6 Why this may be worrying We normally think it is our conscious choices that make us do what we do: But Libet is saying: 6

7 Why this may be worrying But if that s all he s saying, then W could contribute to the action or partially cause it; and he did find that actions could be vetoed. For this to be really a problem, this would have to be the case: 7

8 Vetoes and problems: 1 Amongst various problems, the most salient three are as follows Does W contribute causally to A, or is it causally inefficacious? If Libet is worried about W being causally inefficacious, what is his evidence for this? It may be that RP is necessary but not sufficient for A. What if RP is caused by antecedent reasoning and planning, so that the agent in question is primed to act? Just because your actions are ultimately carried out nonconsciously, does not mean they were not freely chosen in accordance with rational goals beforehand. Why is Libet worried that W, qua mental is not causally efficacious, but he thinks that V is? 8

9 Vetoes and problems: 2 Libet says, and I quote: It might be argued that unconscious initiation applies to the kind of spontaneous but perhaps impulsive voluntary act studied here, but not to acts involving slower conscious deliberation of choices of action.... Even when a more loosely defined conscious preplanning has appeared a few seconds before a self-initiated act, the usual specific conscious intention to perform the act was consistently reported as having been experienced separately just prior to each act by all subjects... This leads me to propose that the performance of every conscious voluntary act is preceded by special unconscious cerebral processes... (Libet, 1985, p536). But then he says: Would the appearance of a conscious trigger or veto also require its own period of prior neuronal activity, as is postulated for the development of the conscious urge or intention to act and for a conscious sensory experience? Such a requirement would imply that conscious control of the volitional outcome, whether by veto or by an activating trigger, is itself initiated unconsciously. For control of the volitional process to be exerted as a conscious initiative, it would indeed seem necessary to postulate that conscious control functions can appear without prior initiation by unconscious cerebral processes, in a context in which conscious awareness of intention to act has already developed (p538, ibid.) 9

10 Solving the problems: 1 Q: Does W contribute causally to A, or is it causally inefficacious? If Libet is worried about W being causally inefficacious, what is his evidence for this? It may be that RP is necessary but not sufficient for A. A: Libet believes W is epiphenomenal. Furthermore, W appears simultaneously with M, so W could not causally contribute to M. Therefore A is caused nonconsciously 10

11 Solving the problems: 2 Q: What if RP is caused by antecedent reasoning and planning, so that the agent in question is primed to act? Just because your actions are ultimately carried out nonconsciously, does not mean they were not freely chosen in accordance with rational goals beforehand. A: This is a legitimate concern. Libet s answer is: Some may view... free will as operative only when voluntary acts follow slower conscious deliberation... But... any volitional choice does not become a voluntary action until the person moves. (ibid., pp538-9). Libet(2001) argues that it is not that chain of reasoning which is causally efficacious in moving the body at least not directly but rather it is the act now event which ultimately causes the act (p61). Libet s argument in defense of this view is simple: We can muse and reason all day, even taking decisions about what we will do, but never actually act (Libet, 1985, pp538-9). It is only when we experience the act now kind of decision that our body actually does something. 11

12 Solving the problems: 3 Q: Why is Libet worried that W, qua mental is not causally efficacious, but he thinks that V is? A: This is inconsistent. Either both must be epiphenomenal or neither. His evidence in fact indicates that V is epiphenomenal as well because V occurs after M (M is at -0.2 sec and V is at sec), therefore V cannot contribute to action because it has already been initiated by M. 12

13 Solving the problems: 3 Libet should, as a materialist, postulate that there is an antecedent brain event to explain V. He found (1982) that all mental states are preceded by brain events occurring 0.2 sec before. Thus: 13