Oliver Sacks: The River of Consciousness

     Oliver Sacks. The River of  Consciousness (2017) Posthumous collection of essays assembled from notes and edited from drafts. As the title suggests, Sacks is thinking about consciousness, the hard problem of philosophy and neurology. In one essay he wonders if consciousness is a discontinuous sequence of moments.
    Vision seems to be discontinuous he says, citing experiments measuring the response times to changes in the visual field. I think it's obvious that vision is discontinuous: the light-sensitiva molecules in the retinal cells decay when struck by light, and must be rebuilt in order to decay again. This process takes about 1/10th of a second. Then the nerve signals generated must be processed so that the human can see. This can take longer than a 1/10th of a second, since objects must be recognised, etc. The fastest conscious reaction times to an expected visual stimulus is about 1/6th of a second in children and teenagers, and double or triple that in adults. Responses to unexpected visual stimuli take much longer. Thus the visual contents of consciousness are constructed from perceptions that take a sizeable time to assemble. the same applies to the other senses. The unbroken stream of consciousness is an illusion. It can be a dangerous one, since what feels like an instantaneous reaction takes at least half a second. At highway speeds a car travels about 14 metres in 1/2 a second.
     Sacks also has interesting observations of the subjective passage of time. His patients vary enormously in the rate at which they process sensory information, and that processing relates to the feeling of time passing. He tells of taking photographs several  minutes apart of one of his post-encephalitic patients, then binding the prints into a flip-book, and seeing the patient slowly lift his arm. Conversely, some of his patients entered a high-speed phase, and reported that they found the world around them moving unbearably slowly.
     The book feels unfinished. Most of the essays consist of extended notes. Sacks didn’t have time to rewrite for continuity, style and clarity, and this sometimes shows in a banal or cliche phrase. However, for any fan this is an essential book. For the general reader it serves as a very good introduction to some of the conundrums of consciousness and mind. ***½
     Correction 2018-11-10: At highway speeds of about 100km/h, a car travels about 14 metres in 1/2 a second.