"Netrage" caused by hardware?

The term "netrage" could become much more common in the future. This is because of the following experience I have had .....

For a couple of years that I have been using the PC at home, I noticed that after about an hour's session, I could no longer concentrate on what is going on on the screen (TFT/LCD) and have to come away and take a rest. What's more, when coming away from the PC, I notice that I didn't feel quite right - I felt vaguely agitated, my mind felt fuzzy and I noticed that I was in a bad mood. It took maybe 15 to 20 minutes rest before I felt "normal" again. Now, I had always thought that this sensation was either specific to this PC/screen combination or was part and parcel of using a computer. My partner also reported a similar sensation, so I knew that it was not just me.

However, due to an unexpected failure of this PC, I decided to put together a second PC. This new machine had almost the same components as the previous one bar the graphics card, which was a similarly basic one but using a different chipset. The first thing I noticed was that I could work on the new PC for a lot longer period of about 2 hours before concentration problems set in. And afterwards, there was not that unpleasant sensation that came after using the previous PC - I was left in a better mood as well. Since I had retained the same screen on the new setup, I concluded that the graphics card was to blame for the premature tiredness and agitated feelings.

It is not clear why the graphics card can cause this problem. My thoughts were that the screen changes (refreshes) could be a factor. Both myself and my partner noticed that on the old machine, surfing the WWW was worse than just wordprocessing. When on the internet, there is more movement on the monitor as you go from one page to another. This visual activity is added to by the need to scroll down pages and the gratuitous animated graphics that adorn many sites. Perhaps how the graphic system of the PC handles the changes on the screen affects our brain through the eyes. After all, we know that flashing lights of certain frequencies can cause epileptic fits. It is perfectly possible that this mood changing ability can be affecting many people to different degrees and can result in "netrage". To a lesser degree, it might just leave us with a bad mood and a feeling of agitation.

Some details of the graphics cards I used follows.
Old Card: ATI Rage 128 Pro with 32 MB of graphics memory, AGP 4x.
New Card: NVIDIA MX 4000 with 64 MB of graphics memory, AGP 8x.
Both cards were connected to a 15-inch TFT monitor via an analogue interface. I have ordered another TFT monitor with a DVI interface as the new card has a DVI output. If there is much difference when using the DVI interface, I will post an update here.