It is well known that novice users often find traditional scrollbars counterintuitive: ”How come the document moves upwards when I’m scrolling downwards?” The reason for the confusion is the faulty mental model the user has created – due to the problematic system image. When moving the scroll thumb, one does not actually move the document but the viewpoint, hence the direction is inverted.
In the case of a hand tool the direction is more intuitive. Once the document is grabbed and the hand is moved downwards, the document moves like it would in real life.
The other day when I was fiddling with my iPod touch and computer simultaneously, it suddenly occurred to me that the same phenomenon is demonstrated there as well. Having just scrolled a list on iPod and trying to scroll a webpage in Safari using the two finger scroll gesture, I ended up moving to the wrong direction. iPod works like the hand tool, whereas the scroll gesture mimics traditional scroll bars.
This got me thinking how this is implemented in the new MacBook Air with its new gesture-capable trackpad. As can be seen in the video, Air works like other laptops and the gesture used for flicking through photos is exactly the opposite to the one used on iPhone. In order to advance you flick from right to left on iPhone and from left to right on MacBook Air. This is the difference between the direct interaction of a touchscreen and the indirect of a trackpad.
It is worth noting, though, that when it comes to rotating photos, the mapping is direct again. When fingers are rotated clockwise, also the photo rotates clockwise. Interestingly, what feels intuitive can change so abruptly between different gestures.