From Towards a Science of Consciousness 3
Section 8: The Timing of Conscious Experience CogNet Proceedings
In his recent book (Penrose 1994) Roger Penrose suggests that
"if,in some manifestation of consciousness, classical
reasoning about the temporal ordering of events leads us to a
contradictory conclusion, then this is strong indication that
quantum actions are indeed at work!" Here we examine a quantum
theory of the relationship between the awareness of timings of
events and their corresponding physical correlates and show that
indeed not only are quantum actions at work, they are indispensable
in explaining the temporal paradoxes inherent in the phenomena.
The problem is that physical events eliciting awareness take place after one becomes conscious of them. This has been indicated in experiments performed by Benjamin Libet and his co-workers (Libet et al. 1979) who hypothesize that a specific mechanism within the brain is responsible for the projection of these events both out in space (spatial referral) and back in time (temporal referral). Libet refers to this as the delay-and-antedating hypothesis/paradox.
My model (called TTOTIM) provides a plausible resolution of this paradox. It is based the work of Aharonov and his co-workers on two-time observables (TTO) (Aharonov et al. 1985, 1987; Aharonov and Vaidman 1990) and on Cramer's transactional interpretation (TI) (Cramer 1986, 1983).
Since many plausible arguments have been offered and refuted by Libet et al. and others (Bergenheim et al. 1996) I will not go into them here.
My TTOTIM theory links mentaland neuralevents. Awareness (mental events) arise as a result of the projection of brain events into space and back in time to the loci of physical events. Thus a conscious experience occurs if and only if at least two physical events occur. Hence neuronal adequacy and subjective experience are not one and the same. Neither are peripheral stimulation and subjective experience even though they seem to be. Both stimulation and neuronal adequacy (two events) are needed for conscious experience. The time of that experience is retro-referred close to the time of the elicitation of the sensory signal.
The TTOTIM sheds light on both "subjective referral in time" as well as "subjective referral in space." Libet (Libet et al. 1979) suggests that neuronal adequacy following a peripheral sensation is temporally and spatially projected onto the peripheral site similar to the way visual experience is projected. The achievement of neuronal adequacy following a peripheral stimulus elicits a backward-through-time signal and the somatosensory cortex (SI) upon achievement of neuronal adequacy must relay this signal out to the physical location of the stimulus. If the stimulus is applied to the brain itself the theory predicts this projection must occur forward-in-time.
[figure 30.1 about here; figures not yet available]
In figure 30.1 we look at how these two stimuli compare when both are used. We see two signals applied. At t = 0, SS causes a quantum wave vector, | S >, to travel forward in time. However at t = .5D, CS is applied interrupting and interfering with the state vector. Neuronal adequacy for SS is not achieved. Instead a quantum wave vector, |na C > , travels forward in time. As time continues a train of signal pulses is elicited leading to neuronal adequacy at t = 1.5D (around .75 sec). This in turn elicits a state vector, |pS>, that travels forward in time arriving at t1.5D+ at the appropriate skin area. Next the time reversed echo state vector, <pS|, goes back in time to t = D where it initiates the backward-through-time state vector, <na C| (not shown), that returns to the onset site of the original cortical stimulus and completes the circuit. There is no awareness of SS although a phantom skin sensation produced by the cortical train is felt later if the wave train duration is sufficient. The phantom event for conscious awareness does not occur at a precise time but subjectively accordingly somewhere in the interval t between time t = 1.5D and t = 1.5D+ (t1.5D+).
One would think from this that the paradox has been resolved. However a question arises when we compare these stimuli with direct stimuli to the thalamus or medial lemniscus just below the thalamus. Signals applied there, unlike cortical stimuli, do elicit time marker signals at SI. Thus one would expect according to Libet's hypothesis, a similar antedating for the awareness of such signals when compared with cortical signals. Although this has been confirmed in a number of studies (Libet et al. 1979) there is a difference in the timings predicted by the TTOTIM.
[figure 30.2 about here; figures not yet available]
In figure 30.2 we compare two stimuli (SS at t = 0- -5msec and Lat t = 0) each eliciting a simultaneous time marker signal (t = 0+10 msec) and achieving simultaneous neuronal adequacy (t = D).Yet they are not experienced simultaneously. The thalamus (L)phantom skin stimulus is felt slightly later at t0++ (20 msec) provided the Lsignal train duration is sufficient to achieve adequacy. The real skin stimulus is felt earlier t0.
Both Sand Lsignals elicit time markers signals at SIwhile Csignals don't. Libet explains that all signals regardless of where the onset site exists require adequacy-a time delay to become conscious. My theory explains the time order of the awareness of passive stimuli events and predicts that phantom or projected experiences whose origins are brain-based will appear later than their associated time marker events (if they occur) while peripheral stimuli will become conscious earlier than their time markers. It answers the question, "How are we to explain the fact that even though L elicits a time marker signal, there is no awareness of this signal unless neuronal adequacy is achieved?" The answer becomes apparent when we realize that spacetime projection and therefore sensation does not occur unless neuronal adequacy does and then it occurs in reference to the time marker.
[figure 30.3 about here; figures not yet available]
In figure 30.3 we see a TTOTIM explanation of Libet's hypothesis/paradox temporal reversal relationship between the timings in cortical and skin stimuli. Here two stimuli are applied with a delay of fD (0f1),between them. At t = 0a cortical stimulus is applied (CS), which leads to a quantum wave vector, |na C >, initiated at the cortical stimulus site SItravelling forward in time leading to neuronal adequacy at t = Dand a phantom state vector, |pS>,arriving at t = D+at the area of the skin associated with the particular site SI. Next the time reversed echo state vector, < pS|, goes back to t = Dwhere it initiates the backward-through-time state vector, <na C|, that returns to the onset site of the original cortical stimulus at t = 0completing the cortical cycle. At t = fDa skin stimulus is applied (SS) leading to a quantum wave vector, |S>, travelling forward in time to t = fD+at L SIwhere it initiates a time marker signal. As time continues the state vector, |na S>, propagates forward in time leading to neuronal adequacy at SI,which occurs after the delay time (1+f)D.Next the time-reversed echo state vector, < na S|,goes back in time to t = fD+where it initiates the backward-through-time state vector, <S|,that returns to the site of the skin stimulus completing the cycle. Subjectively the phantom awareness of the cortical signal appears to occur in the interval tc between t = Dand t = D+ (tD+) while the event for conscious awareness of the skin stimulus occurs somewhere in the earlier interval, ts, between t = fDand t = fD+(tfD).
Since the cortical stimulus does not elicit a time marker signal, the corresponding phantom skin projection occurs well after the skin stimulus projection. It is only when the fraction f = 1,corresponding to the skin stimulus being applied Dlater are the stimuli sensed to be simultaneous.
One of the new and exciting predictions of this theory is the difference between the timings of phantom (thalamic) and real sensory stimuli. Hence we will sense "real" things before we project our mental maps of these experiences onto them but will compare these sensations slightly later. If two time markers are made to simultaneously arise one coming from Land the other from SS,the SSsensation will become conscious 10 msec before and the Lsensation will become conscious about 10 msec after. This appears to be tentatively borne out by experiment (Libet et al. 1979, p. 210). The results are close, to be sure, and it is natural and necessary that they be close, to be encouraging for a quantum physical theory. Assuming that images, memories of sensory inputs, and real sensory data involve the thalamus and the specific projection system within (and consequently elicit time markers), it would follow that the overlap between what we sense "out there" and what we project "out there" as experience must occur in close temporal proximity. This may be the reason for the early evolutionary development of the specific projection (lemniscal) system. Clearly any long delay between sensory inputs and cortical projections (memories or sensory images) that do not elicit time markers could lead to extinction of the species.
Finally I would like to add some thoughts regarding peripheral somatic stimuli, Parkinson's disease, and some prospects for further experimental research regarding the TTOTIM. Libet has already indicated that when the body is subjected to synchronous stimuli, the subject responds without any indication of asynchrony or subjective jitter. If there was no backward-through-time projection from the time when neuronal adequacy was achieved, given that a variety of stimuli would produce a variety of intensities and pulse/train duration, one would expect to experience a lot of jitter owing to the various times when adequacy would be achieved. Since this does not occur it indicates support for the theory.
It is now known that people suffering from Parkinson's disease suffer from what appears to be asynchronous jitter. I suggest that a Parkinsonian subject's thalamus in response to somatic stimuli has lost the ability to provide adequate time marker signals. Consequently synchronous stimuli result in asynchronous behavior or the familiar jitter observed. When electrical stimuli are delivered to the thalamus it is known that the subject's jitter stops or is minimized considerably. I suggest the electrical stimulation provides an artificial supply of time markers. Experiments with Parkinsonian subjects may offer a new source of experimental information regarding the specific projection mechanism and the proposed projection timings indicated by the TTOTIM.
Very little has been done by physicists about subjective experience and for probably very good reasons; no one knows what to do, what to measure, or even if it is ethical to perform such measurements if we knew what we were looking for. Here Libet's remarkable experiments need special mention. At least in them we are provided with a clue concerning subjective time order. Perhaps there is something fundamental in the notion that our equations are not time order unique and (e.g., the theory given here) that we need two or more separate physical events to have a single mental perception. Perhaps this theory that a perceived event requires information flowing from physical end points coming before it and after it, much like a stringed musical instrument requires information coming from its nodal end points to set up standing wave patterns of musical harmony, is a fundamental requirement for both time order uniqueness and subjective experience.
Thus we need to look toward altering our concept of time in some manner, not that this is an easy thing to do. Perhaps we should begin with the idea that a single event in time is really as meaningless as a single event in space or a single velocity. Meaningful relation arises as a correspondence, a relationship with some reference object.
The resolution of temporal paradoxes particularly as they show themselves in future quantum physical objective experiments and in subjective timing experiments will continue to require a new vision of time and its relation to awareness. Perhaps this chapter will assist us in our search.
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