I recently wrote a short essay for 3Quarksdaily on the three second rule of temporal perception and processing in the human brain. It is comparatively easy to measure the thresholds that our brain uses to create temporal structure, i.e. the minimum time interval required to correctly tell apart the sequence of brief sounds or images. It lies somewhere in the range of 30 milliseconds to 60 milliseconds. If healthy subjects hear two auditory clicks (one in the right ear and one in the left ear) which are only 10 milliseconds apart, they may be able to identify them as two distinct stimuli, but they may not be able to say which one came first.
Temporal integration, on the other hand, refers to combining sensory information and creating the sense of a subjective present or the perception of a “now”. It is not possible to directly measure it, but many observational studies point to a “three second rule” of temporal integration in the brain. One of these studies involved the analysis of poetic meter and was conducted by the chairman of the department in which I used to work when I was a student. The study found that the average time it takes to recite individual verses of poems from all around the world is approximately three seconds. Since each verse (the authors use the more generic term “LINE” to accomodate poems which use a different orthrographic notation or which allow for pauses when reciting long verses) is considered to be an independent unit that is intended to evoke certain poetic “moments”, the authors surmise that the global convergence of verse length may be due to the fact that our brain is most comfortable with three-second intervals to create the sensation of the “now”. This is obviously anecdotal and observational, and not a definitive finding, but it is still fascinating. It does not “prove” that our brain perceives the “now” in three second intervals, but when combined with other cognitive studies of temporal integration, it supports the notion that three seconds may be an important temporal unit for our brain.
The complete essay can be found here: http://www.3quarksdaily.com/3quarksdaily/2013/07/three-seconds-poems-cubes-and-the-brain.html.
You should consider reading some of the original references that are linked in my 3Quraksdaily essay, such as the classic study published in the Poetry magazine, which is (thankfully) open access and can be read by everyone. It is a remarkable example of how a collaboration between a cognitive scientist (my former chairman) and a poet which won a prestigious poetry award when it was published in 1983.