Darren Rowse at the site Digital Photography School posted a review of Lenovo's ThinkPad W700ds notebook. You may not recognize the model number but you've probably seen a photo of it -- it's the beast with two screens and a built-in Wacom digitizing tablet.
"the touchpad really is small"
Back to the W700ds, which has a Wacom tablet right where you might rest your hand. It isn't sensitive to finger input so there's no risk of accidental input, but users may still not like it. Darren writes:
That observation makes me wonder whether we shouldn't just leave the palmrests for the palms. Nevertheless, I'm very interested in what you could do with huge touchpads covering the palmrests. (And lots of other people have thought about this previously too.) Here's a mockup:
To my thinking there is a benefit in dividing the touchpad into two regions, one for each hand. The dividing line could either be real or imaginary -- there could just be two touchpads side-by-side or there could be one wide touchpad with a virtual invisible dividing line.
Two-handed input has been the subject of a lot of HCI research that argues that we'd have better user interfaces if we did a better job of balancing the interactions across both hands (see for example Mackenzie and Guiard, 2001).
Much of that research builds on Yves Guiard's kinematic chain model that says (approximately) that people often use their two hands in concert like two links in a chain. The dominant hand is like the bottom link and does finer manipulations, while the non-dominant hand is like the top link and frames what the other hand does. A common illustration of this is handwriting: people tend to use both hands when writing on paper -- one hand to write and the other to continually reposition the paper.
There are some possible dual-touchpad interaction techniques that are analogous to this. For example, you might have a mode where the left touchpad allows scrolling and panning while the right allows pointing (for right-handed users). Bill Buxton and others have shown that even though users are still not likely to scroll and point in parallel, the interface is more efficient because of a cognitive benefit in splitting the tasks across the hands (see Leganchuk et al., 1998).
Another asymmetric technique that you could implement on dual touchpads is the Toolglass technique (see Bier et al., 1993) where the left hand positions a toolbox and the right hand selects tools from it.
Some gestures also might work better with two hands instead of one (see Moscovich 2008 for an experiment on this). Scaling an image is likely to be done more precisely with two index fingers than with the thumb and finger on one hand.
I'm hoping to set up a dual-touchpad prototype and test some of these ideas. I welcome any comments... Would you buy a laptop with two touchpads?