Westerhoff, J. (2011). Reality: A very short introduction. Oxford: Oxford University Press.
Added by: Mark Grimshaw-Aagaard 18/08/2024, 15:00
"The different information coming in from our senses, visual, auditory, tactile, olfactory, and gustatory sensations are processed in different regions of the brain. They have to travel different distances [...] and arrive at different times. The processing speed for different kinds of sensory information varies; visual stimuli take longer to process than other stimuli. (The difference is about 40 milliseconds. [...]) On the other hand, light travels much faster than sound. Putting together these different speeds means that sights and sounds from about 10 metres away are available to consciousness at about the same time; for everything closer or further away information about its sight or sound arrives at different times. In these cases, the apparent simultaneity of, for example, hearing a voice and seeing the speaker's lips move has to be constructed by our brain."
Discussing Libet's (1985) experiment. While we prefer to believe that we have willed our hand to rise, our intention, there is a precursor in the subconscious, the readiness potential, that can be measured using EEG and that precedes the hand movement and the reported time at which subjects noted their intention to lift the hand. The conclusion is that intention (and thus free will?) is manufactured after the event. See also (Rosenberg 2018, p.99).
Detailing a set of experiments by Libet helping to explain how our brain builds a consciousness of the present and the time delay involved.
Stimulating the brain directly, an electrical impulse must be applied for at least 500 milliseconds to produce a perception (see, for example Libet 1985). Shorter impulses had no effect neither did increasing the intensity (with shorter times). Sensation can be detected by the brain within 500msecs but the subject is not consciously aware of it (e.g. we can react 'instinctively').
Stimulate the skin then, 200 milliseconds after, stimulate the brain – the skin stimulation is not perceived but is masked by the brain stimulation. The brain edits past events to give an impression of the 'present'.
Stimulate the brain then, 200 milliseconds later, stimulate the skin. Brain stimulus is perceived after about 500msecs but the skin stimulus is perceived as being before the brain stimulus. A temporal reordering: "There is no guarantee that the order in which we perceive events actually corresponds to the order of their occurrence" (Westerhoff 2011, p.100).
