A study in the journal Current Biology goes some way to explain why thinking ability in some people decreases as they get older and the key factor was the loss of ability to process visual information quickly or ‘at a glance’.
The study compared how quickly older people took in information at a glance and also their ability to perform more complex unrelated tasks. They found that these 2 skills were very tightly linked suggesting a possible link between quick visual input and retaining a sharp mind
This goes some way to explain why as people get older, they are less able to process information quickly from a fleeting glance and need to take more time to study before being able to digest the information, such as seeing a new face enter the room.
It would be interesting to further this study to see how much a decline in actual vision affects this process. At the moment the study looks at how the brain is digesting what the eyes are seeing. I would be interested to see if the findings varied according to the individual’s eyesight. After all the eyes have to see the information clearly to be given a chance to process it quickly and accurately.
We already know that a normal ageing eye loses transparency (you need about 3x as much light input aged 60 to see as clearly as you do at 20) even without any conditions such as cataract, all the more reason to make sure you are getting your eyes examined regularly and keeping you glasses or contact lens prescription up to date especially as you get older.