12 January 2015
The dimension of the present moment
Apparently, the present moment — our sense of "now" — lasts about three seconds.  It is part of an illusion created by the brain and sits in a hierarchy of processes between the functional moment, which is the brain's response time to stimuli (typically in thousandths of a second ) and a sense of mental presence, which operates over a timespan of about thirty seconds and gives us a sense of continuity. 
In a collection of essays published in 1990, Mirsolav Holub noted that the dimension of the present moment, at about three seconds, is roughly the same amount of time as it takes to speak a line of poetry. And language, of course, plays an important role in our ability to place ourselves in much longer stretches of time. 
 see Laura Spinney The time illusion: how your brain creates now, drawing on Moments in Time by Marc Wittman.
 The auditory system can distinguish sounds that are two milliseconds apart. The visual system requires tens of milliseconds. Two events must be at least 50 milliseconds apart before you can tell which came first. But the computation in the brain involved in understanding sounds is much slower (see this).
 Thirty seconds being the amount of time that experienced moments are held together in short-term, or working memory.
 Brief overviews of the science of time: this by Sean Carroll and this by Jim Holt.
Image: Étienne-Jules Marey