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Fitt's law - Arvind Narayanan's journal [entries|archive|friends|userinfo]

Fitt's law [Jun. 13th, 2004|12:47 am]
Arvind Narayanan
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The last few days I've been starting to go on a sort of crusade to get more of GNOME to be Fitt's law-aware. Now I'm trying to put down in one place what I think needs to be done and why its important.

Try this experiment: use your mouse with your left hand for a minute or two (or if you're a left hander, with your right hand). Just do simple standard stuff -- moving/resizing a window, clicking a button etc. Notice how hard it is? Believe it or not, for many non-techie computer users, using a mouse (with their regular hand, that is) is as hard as it was for you just now.

Perhaps you're snorting. What can be so hard about using a mouse, you wonder. After all, you've done it with supreme ease for as long as you can remember. But keep this in mind: Nipples are natural. Everything else has to be learned. Since it is doubtful that a computer interface interface based solely on sucking on nipples will be invented any time in the near future, we have to focus on making our existing interfaces as easy to use as possible. And for people who use computers only once in a while, it can take a long time to get comfortable with mice.

Fitt's law is one of the principles of Human-Computer Interaction that lets us take these factors into consideration. Although its statement, "the effort required to acquire a target is a function of the size of the target and its distance from the current pointer location" sounds obvious, it's amazing how often the law is ignored.

One special case makes the law non-trivial: the screen is modeled as an infinite surface, and the edges of the screen are considered extend unto infinity in the respective directions. The 4 corners are the 4 easiest pixels of the screen to reach, because you can "throw" your mouse at them. Not only does this provide a horizon of stability for those whose mouse movements are like a ship thrashing in a chaotic ocean, it also greatly increases the efficiency of users with good mouse control. So the aim must be to populate the edges of the screen with as many UI elements as possible.

How does GNOME stack up?


[User Picture]From: fallibledragon
2004-06-12 12:33 pm (UTC)
Ohh, that's interesting. I was wondering where you were going with this, but I've definitely noticed that close buttons in the top corners etc. are relatively easy. And I'm a guy with so much mouse experience that I can use it left-handed or even from the other side of the desk while looking down at the screen!

I find docks and things very easy too. There was something about the Dungeon Master game that I found incredibly intuitive. The panels for game control were top and right, rather than top and left like most games or user-interfaces. It meant that you would control with your right hand hand using stuff on the right, and, if you're facing the computer straight on, most of your body is "free" in the visual area of the screen. Seems to me that the orientation of panels, docks, etc. should be able to change according to the screen setup.

It'd be complicated, though -- rather than just settings for the kind of speakers and layout of multiple monitors, you'd need to extend it to a 'workstation layout' configuration, or something.

Then again, I've only read a little user-interface stuff, so maybe this is wrong-headed of me :)
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[User Picture]From: arvindn
2004-06-13 12:46 am (UTC)
That's Ok -- I haven't read a lot of user-interface theory either :) Just the basics.

Anyway, what I understand is that in Dungeon Master the user gets the illusion of having more free space if the controls are to the right instead of left? That sounds very interesting.
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[User Picture]From: fallibledragon
2004-06-13 01:30 am (UTC)
Yes; something like that. I suppose I'd say more 'freedom' rather than free space -- in other layouts, I feel sort of restricted, because my mouse needs to cross my whole visual area, and it feels a little like crossing my arms to write on the far side of a page. But in DM, you're looking across/past the controls, into the lower left of the screen. It feels like the mouse only goes there because you explicitly want it there, and that you can easily move it back to the controls without disturbing the view much.

I guess the easy way to look at it is this: which side of a page do you scribble notes on as you read? For me, it's the right -- I don't want to read while my arm is across the page writing notes on the left. It feels similar, though more subtle, with a mouse for me.

Anyway. It could be just me :) And, I think it'll be different for left-handed people. I'm not sure how this would work with people who naturally write right-to-left. Perhaps it's the opposite then.

Anyway. I know a lot of people consider dungeon master one of the most playable and atmospheric games of all time, and I don't want to diminish the other great aspects of the game, but I think that has at least a little bit to do with it :)
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[User Picture]From: fallibledragon
2004-06-13 01:33 am (UTC)
Oh yes... Deluxe Paint, one of the most popular paint packages in the 16-bit world, had a similar layout. I found that very natural, too :)
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