This article was originally published in September 2020.
What is the duration of the present moment? How is it that this present moment is replaced by ‘the next moment’? Within every organism, sentient or not, there are thousands of chemical processes that occur with their own characteristic time periods, but these time periods start and stop at different times so that there is no synchronized ‘moment’. Elementary atomic collisions that build up molecules take nanoseconds while cell division takes minutes to hours, and tissue cell lifespans vary from two days in the stomach lining to eight years for fat cells (see Cell Biology). None of these jangled timescales collectively or in isolation create the uniform experience we have of now and its future moments. To find the timescale that corresponds to the Now experience we have to look elsewhere.
It’s all in the mind!
A variety of articles over the years have identified two to three seconds as the maximum duration of what most people experience as ‘now’, and what researchers call the ‘specious present’. This is the time required by our brain’s neurological mechanisms to combine the information arriving at our senses with our internal, current model of the ‘outside world’. During this time an enormous amount of neural activity has to happen. Not only does the sensory information have to be integrated together for every object in your visual field and cross connected to the other senses, but dozens of specialised brain regions have to be activated or deactivated to update your world model in a consistent way.
In a previous blog I discussed how important this world model is in creating within you a sense of living in a consistent world with a coherent story. But this process is not fixed in stone. Recent studies by Sebastian Sauer and his colleagues at the Ludwig-Maximilians-Universität in Munich show that mindfulness meditators can significantly increase their sense of ‘now’ so that it is prolonged for up to 20 seconds.
The knitting together of these ‘nows’ into a smooth flow-of-time is done by our internal model-building system
In detail, a neuron discharge lasts about 1 millisecond, but it has to be separated from the next one by about 30 milliseconds before a sequence is perceived, and this seems to be true for all senses. When you see a ‘movie’ it is a succession of still images flashed into your visual cortex at intervals less than 30 milliseconds, giving the illusion of a continuous unbroken scene. (Dainton: Stanford Encyclopedia of Philosophy, 2017).
The knitting together of these ‘nows’ into a smooth flow-of-time is done by our internal model-building system. It works lightning-fast to connect one static collection of sensory inputs to another set and hold these both in our conscious ‘view’ of the world. This gives us a feeling of the passing of one set of conditions smoothly into another set of conditions that now make up the next ‘Now’. To get from one moment to the next, our brain can play fast-and-loose with the data and interpolate what it needs. For example, in our visual world, the fovea in our retina produces a blind spot but you never notice it because there are circuits that interpolate across this spot to fill in the scenery. The same thing happens in the time dimension with the help of our internal model to make our jagged perceptions in time into a smooth movie experience.
Neurological conditions such as strokes, or psychotropic chemicals, can disrupt this process and cause dramatic problems. Many schizophrenic patients stop perceiving time as a flow of linked events. These defects in time perception may play a part in the hallucinations and delusions experienced by schizophrenic patients, according to some studies. There are other milder aberrations that can affect our sense of the flow-of-time.
