In the visual system, the represented features of individual objects (shape, colour, movement, and so on) are distributed both in space and time within the brain. Representations of inner and outer event sequences arrive through different sense organs at different times, and are likewise distributed. Objects are nevertheless perceived as integrated wholes - and event sequences are experienced to form a coherent "consciousness stream." In their thoughtful article, Dennett & Kinsbourne ask how this is achieved.

Four experiments examined how accurately participants can report the times of their own decisions. Within an auditory reaction time task, participants reported the time at which the tone was presented, they decided on the response, or the response key was pressed. Decision time reports were checked for plausibility against the actual RTs, and we compared the effects of experimental manipulations on these two measures to see whether the reported decision times showed appropriate effects. In addition, we estimated the amount of (...) error associated with individual decision time reports by checking how often participants’ decision time reports were implausibly early or late , and by using several quantitative models. Overall, the results suggest that decision time reports are not very accurate but they may be usable for some purposes. (shrink)

Neuroscientific studies have shown that brain activity correlated with a decision to move can be observed before a person reports being consciously aware of having made that decision . Given that a later event cannot cause an earlier one , such results have been interpreted as evidence that decisions are made unconsciously . We argue that this interpretation depends upon an all-or-none view of consciousness, and we offer an alternative interpretation of the early decision-related brain activity based on models in (...) which conscious awareness of the decision to move develops gradually up to the level of a reporting criterion. Under this interpretation, the early brain activity reflects sub-criterion levels of awareness rather than complete absence of awareness and thus does not suggest that decisions are made unconsciously. (shrink)

An extended examination of Libet's works led to a comprehensive reinterpretation of his results. According to this reinterpretation, the Minimum Train Duration of electrical brain stimulation should be considered as the time needed to create a brain stimulus efficient for producing conscious sensation and not as a basis for inferring the latency for conscious sensation of peripheral origin. Latency for conscious sensation with brain stimulation may occurafterthe Minimum Train Duration. Backward masking with cortical stimuli suggests a 125-300 ms minimum value (...) for the latency for conscious sensation of threshold skin stimuli. Backward enhancement is not suitable for inferring this latency. For determining temporal relations between stimuli that correspond to subjects' reports, theendof cerebral Minimum Train Duration should be used as reference, rather than its onset. Results of coupling peripheral and cortical stimuli are explained by a latency after the cortical Minimum Train Duration, having roughly the same duration as the latency for supraliminal skin stimuli. Results of coupling peripheral stimuli and stimuli to medial lemniscus (LM) are explained by a shorter LM latency and/or a longer peripheral latency. This interpretation suggests a 230 ms minimum value for the latency for conscious sensation of somatosensory near-threshold stimuli. The backward referral hypothesis, as formulated by Libet, should not be retained. Long readiness potentials preceding spontaneous conscious or nonconscious movements suggest that both kinds of movement are nonconsciously initiated. The validity of Libet's measures of W and M moments (Libet et al., 1983a) is questionable due to problems involving latencies, training, and introspective distinction of W and M. Veto of intended actions may be initially nonconscious but dependent on conscious awareness. (shrink)

A commentary on articles by Klein, Pockett, and Trevena and Miller, in this issue, is given. Average shift in the point of subjective equality , calculated by Klein on Libet's data, and corresponding change in mean shift, calculated by Libet et al. , may be “corrected,” taking as a reference point the end of the minimum train duration. Values obtained, if significant, indicate a latency for conscious sensation of the skin stimulus of at least 230 ms. Pockett's main conclusions are (...) favored, but her explanation of peripheral–lemniscal couplings is found to be unconvincing. Trevena and Miller's article unsuccessfully tries to rescue a dualist interactionist view. Libet's method of timing intentions is thoroughly criticized. (shrink)

_Behavioral and Brain Sciences_ , 15, 183-247, 1992. Reprinted in _The Philosopher's Annual_ , Grim, Mar and Williams, eds., vol. XV-1992, 1994, pp. 23-68; Noel Sheehy and Tony Chapman, eds., _Cognitive Science_ , Vol. I, Elgar, 1995, pp.210-274.

We report two experiments in which participants had to judge the time of occurrence of a stimulus relative to a clock. The experiments were based on the control condition used by Libet, Gleason, Wright, and Pearl [Libet, B., Gleason, C. A., Wright, E. W., & Pearl, D. K. . Time of conscious intention to act in relation to onset of cerebral activities : The unconscious initiation of a freely voluntary act. Brain 106, 623–642] to correct for any bias in the (...) estimation of the time at which an endogenous event, the conscious intention to perform a movement, occurred. Participants’ responses were affected systematically by the sensory modality of the stimulus and by the speed of the clock. Such findings demonstrate the variability in judging the time at which an exogenous event occurs and, by extension, suggest that such variability may also apply to the judging the time of occurrence of endogenous events. The reliability of participants’ estimations of when they formed the conscious intention to perform a movement in Libet et al.’s study is therefore questionable. (shrink)

Susan Pockett presents sound arguments supporting her reinterpretations of data that Libet and co-workers used to support a number of intriguing and influential conclusions regarding the microgenesis and timing of conscious sensory experience and volitionally controlled motor responses. The following analysis, extending and elaborating some of her main arguments, proposes that Libet's experimental methodologies and rationales, and thus also his interpretation of data, are flawed and that neglect or ignorance of methodological and empirical constraints well known to sensory psychologists risks (...) drawing premature or faulty conclusions about the timing of conscious experience. (shrink)

ABSTRACT For a long time, the question of the existence of free will has fueled philosophical debate with no definitive solution. Libet’s paradigm (1983) seemed to demonstrate that simple and apparently voluntary movements could be triggered not by consciousness, but by preconscious or random brain processes. Such findings had wide repercussions in the academic and scientific circles, triggering an extensive discussion among neuroscientists, philosophers and jurists. Exploring the interfaces between neuroscience and free will, the present work aims to formulate an (...) updated synthesis of the diverse problematizations about the Libetian findings. It appears that Libet’s essay, although repeatedly analyzed and replicated in recent decades, still lacks a definitive interpretation, in part due to methodological controversies and specific conceptual shortcomings. The deepening of these investigations, combined with the new discoveries offered by neuroscience, can enrich research on free will in the coming years. (shrink)

We report two experiments in which participants had to judge the time of occurrence of a stimulus relative to a clock. The experiments were based on the control condition used by Libet, Gleason, Wright, and Pearl [Libet, B., Gleason, C. A., Wright, E. W., & Pearl, D. K. . Time of conscious intention to act in relation to onset of cerebral activities : The unconscious initiation of a freely voluntary act. Brain 106, 623–642] to correct for any bias in the (...) estimation of the time at which an endogenous event, the conscious intention to perform a movement, occurred. Participants’ responses were affected systematically by the sensory modality of the stimulus and by the speed of the clock. Such findings demonstrate the variability in judging the time at which an exogenous event occurs and, by extension, suggest that such variability may also apply to the judging the time of occurrence of endogenous events. The reliability of participants’ estimations of when they formed the conscious intention to perform a movement in Libet et al.’s study is therefore questionable. (shrink)

There are numerous theoretical reasons which are usually said to undermine the case for mental causation. But in recent years, Libet‘s experiment on readiness potentials (Libet, Wright, and Gleason 1982; Libet, Gleason, Wright, and Pearl 1983), and a more recent replication by a research team led by John Dylan Haynes (Soon, C.S., Brass, M., Heinze, H.J., and Haynes, J.-D. [2008]) are often singled out because they appear to demonstrate empirically that consciousness is not causally involved in our choices and actions. (...) In this paper, an alternative interpretation of these studies is offered; one which is in accordance both with the empirical evidence and also with the phenomenology of the will, demonstrating that the two opposing views of agency – both the ones that deny the reality of free will and the ones that affirm it – are equally compatible with the outcomes of these two experiments. On this basis, it is shown that the claim that the results on the timing of readiness potential tip the scales in favour of one or the other view cannot be justified - neither from a neurological, nor from a philosophical perspective. (shrink)