On how our hunting mode affects our perception."
I'll start off by agreeing with Pulltab on one point - sticking to a grid pattern is DIFFICULT. The natural inclination is to wander about your site aimlessly, flitting about like a lost little bumblebee. Pulltab then goes on to extol the virtues of working a dedicated grid pattern. And again, I won't disagree with him, it does have many benefits. That being said, my philosophy is much more fluid than "to grid or not to grid". In my eyes, the grid versus random search pattern is best decided by two key factors: area and time.
I'll use some extreme examples to illustrate my point. First, lets say we're talking about searching your own yard, a historic home on 1/2 acre. You've got basically unlimited time to hunt a small area - to get the most out of it as efficiently as possible, use a three way grid pattern. Tight overlapping swings in one direction, then turned ninety degrees, and finally on the diagonal. Believe it or not, that half acre can keep you occupied for a really long time, and you're still likely to miss some of it.
On the other extreme, take a fifty acre historic fairgrounds an hour's drive away. Does it really matter if you grid or wander? Not really. There's no "bad" ground at a site like that, and as long as you don't go over the same path multiple times, you'll cover the exact same amount of ground randomly as you will gridding. Here I'd probably recommend a random search pattern until you get a hit, investigate the area more closely, and if you find more good hits THEN you can grid the area. A perfect example is the dense grouping of finds in a much larger farm field in my October 8th detecting report.
Of course, most of your sites won't be either of these extremes, but somewhere in between. All I'm saying is, don't be so hard on yourself if you're not a gridder - but gridding is a great technique that you can use to make the most of your sites. Or maybe this is just my rationalization to remove the guilt from my all-too-common random wanderings!