Old codgers everywhere are saying this right now: “We’re a third of the way through autumn already? Geez, the years go by faster and faster”.
Well they seem to – and for years researchers have been trying to figure out why time seems to fly as we age.
According to an intriguing new theory, published this week, the “apparent temporal discrepancy” can be blamed on the ever-slowing speed at which images are collected – or perceived in the surrounding environment – and processed by the ageing human brain.
In short, we don’t see as much as we used to
The study author, Adrian Bejan, the J.A. Jones Professor of Mechanical Engineering at Duke University, explains it this way, in a statement from the university.
As tangled webs of nerves and neurons mature, they grow in size and complexity, leading to longer paths for signals to traverse.
As those paths then begin to age, they also degrade, giving more resistance to the flow of electrical signals. These phenomena cause the rate at which new mental images are acquired and processed to decrease with age.
“This is evidenced by how often the eyes of infants move compared to adults – because infants process images faster than adults, their eyes move more often, acquiring and integrating more information,” Dr Bejan observed.
A slower view of the world speeds time up
The end result is that, because older people are viewing fewer new images in the same amount of actual time, it seems to them as though time is passing more quickly.
“The human mind senses time changing when the perceived images change,” Dr Bejan said.
“The present is different from the past because the mental viewing has changed, not because somebody’s clock rings. Days seemed to last longer in your youth because the young mind receives more images during one day than the same mind in old age.”
The mechanism central to Dr Bejan’s theory is what’s known as “saccades frequency”.
Saccadic eye movements are unconscious, unfocused jerks during which the eye isn’t focused on anything; they occur a few times a second. In between this flickering, our eyes fixate on something and the brain processes what’s being perceived.
There’s a cat on the TV that is playing in the background, for example.
In human infants, those fixation periods are shorter than in adults – and the net result is babies actually see more, and their brains are busier, in the same amount of time.
So, Dr Bejan argues, when you are young and your brain is busy taking in new things, time seems to be pass more slowly.
As you get older, the rate at which we flick from one thing to the other slows down, giving the sense that time passes more rapidly.
Bejan’s theory may be part of a bigger explanation that hasn’t been fully told yet – and certainly fits with earlier theories.
Here is a neat explainer from The Conversation that gives an overview of the issue – including the prevailing idea that “it’s the release of the neurotransmitter dopamine that helps us learn to measure time”.
Beyond the age of 20 and continuing into old age, “dopamine levels drop, making time appear to run faster”.
An experiment that shows it’s a thing
In 1996, in a variation of a common experiment exploring time perception, Peter Mangan, a psychologist at Clinch Valley College in Wise, Virginia, asked 25 people aged between 19 and 24, and 15 older people aged between 60 and 80, to estimate a three-minute interval by counting seconds.
They were told to use the “1, 1000, 2, 1000” technique. The youngsters averaged three minutes and three seconds. For the oldies – all of them still busy people, engaged with life – an average of three minutes and 40 seconds skipped by before they thought three minutes had elapsed.
Dr Mangan speculated that the brain’s internal clock – a theoretical idea of a clock that tracks time intervals, and separate from the circadian clock that controls sleep and wake cycles – runs more slowly as we age. Dopamine being the villain here.
As people age, Dr Mangan noted, brain cells that produce dopamine begin to deteriorate in the basal ganglia and substantia nigra. It’s these regions that contain the workings of this internal clock.