Wednesday, September 25, 2013

Time and time again

For years - any opportunity I have to do any serious thinking typically and inevitably circles around time. What is it, was it always there, how do we perceive it, how is time intertwined by space (space-time) etc. And if we subscribe to Einstein's theory of relativity, there was no such thing as time before the big bang; there was no "before." Time (and space) started at a singularity (with the laws of physics broken down).

And more so, is time a feature of the universe that can be understood independently of a conscious being. That is, can we make sense of time when everything about time is perceived and processed through a lens of brain architecture?

We know for example time is processed across a a highly distributed system involving the cerebral cortex, cerebellum and basal ganglia. One particular component, the suprachiasmatic nucleus, is responsible for the circadian (or daily) rhythm, while other cell clusters appear to be capable of shorter-range (ultradian) timekeeping.

Different types of sensory information (auditory, tactile, visual, etc.) are processed at different speeds by different neural architectures. Our brain, it seems, has learned how to overcome these speed disparities, to create a temporally unified representation of the external world.

In the popular essay "Brain Time", by David Eagleman, he suggests that "if the visual brain wants to get events correct timewise, it may have only one choice: wait for the slowest information to arrive. To accomplish this, it must wait about a tenth of a second.  As long as the signals arrived within this window, viewers' brains would automatically resynchronize the signals". He goes on to say that "This brief waiting period allows the visual system to discount the various delays imposed by the early stages; however, it has the disadvantage of pushing perception into the past. There is a distinct survival advantage to operating as close to the present as possible; an animal does not want to live too far in the past.

Therefore, the tenth-of- a-second window may be the smallest delay that allows higher areas of the brain to account for the delays created in the first stages of the system while still operating near the border of the present. This window of delay means that awareness is postdictive, incorporating data from a window of time after an event and delivering a retrospective interpretation of what happened."

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