There is a further important neurophysiological fact that impinges on our portrayal of conscious processing. And that is that conscious-perceptions are ‘late’: this means that the average time interval between a stimulus and its registration in conscious-awareness is approximately 250–300 milliseconds. Comparatively, that is much slower than the average latency of subconscious processing, whose speed is of the order of tens of milliseconds.
For example, a tennis player in the Men’s Singles Final at Wimbledon will have moved towards the net and returned serve before he is actually con- sciously aware of seeing the ball leave the server’s racket. The reason for this has now been well established. There are two major visual systems both stimulated by light falling on the retina.3Once the light stimulus from the retina has reached the primary (occipital) visual cortex, the systems diverge. The dorsal action ‘stream’ is fast and results in motor responses which are unconscious, while the ventral ‘stream’ is slow and leads to a conscious cerebrally processed percept of the original retinal stimulus. The decision of the player to run to the net and return serve is effected by the dorsal stream responsible for activating the appropriate musculature. Much later, the
2 Chalmers D, The Conscious Mind, Oxford: Oxford University Press 1997, xiii. 3
Mishkin M, Ungerleider L, Macko K, Trends in Neuroscience, October 1983, 414 417.
ventral stream ‘replays’ to the player not only what he thought had actually taken place but what he considered to be his executive responsibility for those actions. Through other experimental means, a subject may come to think that he was responsible for an action when no such responsibility, in fact, was involved.4
From another perspective,5 relative to the continuously rapid scanning (saccadic) sweeps of our eyes, it is estimated that ~20% of our visual life is ‘blind’. The perceived ‘stream of consciousness’ is replayed by the brain as though offering a faithfully video-recorded edition of events already (by 200– 300 milliseconds) gone. Again, we should note that the steady, smoothed and apparently continuous act of ‘seeing’ is a cerebrally, and not retinally, en- gineered event. The constant, rapid bobbing about of our eyeballs has little relationship to what we think we saw, or are seeing. Yet the ‘filling in’ which our brains effect is based on a considerable degree of past experience and therefore statistical knowledge of what the world is like: hence the success of the (unseen) return serve. Probably the same with penalties: I doubt whether a goalkeeper actually sees the ball when kicked from such close range. It may be pure luck whether he moves, falls or stretches out his arms into a saving position.
The other side to visual illusion is characterized by experiences or drawings which emphasize the tricks that our eyes play on us: many are well known. For example, distant railway lines appear to converge at the horizon. There are also the well-known paradoxes of the duck/rabbit phenomenon, or the opposition of facial profiles that can be read, alternatively, as a beautifully sculpted vase. Most of us will be less aware of the illusory states brought about by the neurophysiological mechanisms subserving body-image, and which additionally generate the perceptual construct of egocentric and paracentric body space which are discussed in the following chapter. These perturbations in body-image lie at the root of abnormal experiences such as: first, seeing an autoscopic mirror image of oneself; second, feeling that one’s consciousness is alternating between oneself and one’s double (heautoscopy); third, the sens- ing of external ‘presences’; or fourth, having an OBE.
In exploring the relationships between apparent conscious reality and illusion in relation to ECE phenomenology, I turn to the intriguing, so-called ‘phantom-limb’ phenomenon, and how subjects are deluded into believing that a body part continues to exist. This phenomenology, I think, will give readers unaccustomed to thinking about consciousness a chance to under- stand how easily the brain constructs illusion. Specifically, these examples
4 Wegner DM and Wheatley T, Am Psychol 54: 480 492, 1999. 5
have a bearing on how a subject may experience being out-of-body, or even undergoing a near-death event. Indeed, from the outset, it is highly probable that these phenomena are generated entirely by internal cerebral mechanisms in brains that could hardly be considered to be hypoxic, and certainly not in any sense agonal.6
5 . 2 . ‘ P H A N TO M L I M B’ P H E N O M E N O LO G Y: T H E N E U RO P H YS I O LO G Y O F A B S E N C E
The popularized term for the ‘phantom limb’ phenomenon, was originally coined in 1872 in describing the symptomatology of ninety American Civil War amputees.7This, in its basal form, refers to the continued memory of a body part previously removed through trauma or a planned surgical proce- dure. The phenomenon8 applies to, and is most commonly thought of in terms of a lost limb, but it is also relevant to the severing of an arm, hand or finger; and the resection of a breast, tooth or eyeball. It can also result from removal of an internal organ to which conscious somatic representation applies, such as a diseased uterus for painful fibroids. In the case of a removed bladder or rectum, persistent sensations of crampy abdominal pain, fullness, bursting, evacuation or urgency may extend for considerable intervals post- operatively.