Following a comment on the article Does Light Therapy Work? Some Real Evidence At Last I wanted to look into what effect the flickering of a TV screen has on the brain. As someone who watches too much TV and sits in front of computer monitor all day it is an issue close to my heart.
A TV screen refreshes the picture at 60 times a second (60hz) in the US and 50 times a second (50hz) in Europe. This refreshing happens to fast to consciously see but does it still have an effect?
The first information I found was related to photosensitive epilepsy, i.e. convulsions trigger by flickering lights. According to Professor Harding almost 50% of photosensitive epilepsy patients are sensitive to the european flicker rate where as on 15% are sensitive to the US rate.
Next is Entrainment to Video Displays in Primary Visual Cortex of Macaque and Humans [ PDF ]. This study found that cells in the V1 area of visual cortex did become entrained. Entrainment was greater when the display included strongly contrasted patterns.
This led me to a study on The effects of flicker on eye movement control. This wasn’t using a TV or monitor screen but involved reading printed matter whilst a light flickered at 50hz, 100hz or under a study light.
The results are consistent with the view that flicker has two distinct effects on reading, both of which are potentially disruptive. The first relates to an increase in the number of prematurely triggered saccades, which are, as a result, less accurate. The second is an increase in the number of saccades perturbed in flight, which land short of their intended target.
It is interesting to note that fluorescent lights flicker at 100hz or 120hz depending whether you are in Europe or the US. This suggests that reading under fluorescent lights is harder than reading under steady light. The author of the study, Alan Kennedy, did a second study examining eye movements (Eye Movement Control During the Inspection of Words Under Conditions of Pulsating Illumination), this time reading from a screen flickering at between 50hz and 125hz. This found similar evidence of an effect.
None of this gives a clear message on television flicker and the brain but it does tell us that flicker too fast to be consciously detected does have some effects.