Non-hi def is still a simulated hi-def picture. If processes the standard def picture to fill in the definition to use all of the available pixels.

The size of the picture can also be a problem as well as the sound. If there is too much surround sound, that is a lot of information for the brain to process. I can not handle any surround sound.

Regarding picture size, it is relative to filed of view. The larger the picture, the farther one needs to be from the screen. There is a recommended distance I saw somewhere.

The amount of other visual clutter is also an issue. Since most HD screens are mounted on a wall, they are at the same visual plane as the other wall mounted visual stimuli. Re-arranging the wall hangings and such to be out of the field of view may make a difference.

In time, the brain may get used to the other visual clutter but as we know, many of us do not filter out visual clutter very well.

It is only going to get worse as the TV producers try to use the HD to include more graphics and such into the programming. The graphics for football are driving me batty, even in standard definition.