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I came across an interesting research paper on the topic about the thumb's contact size for single-handed mobile interaction. It got me thinking about the difference in how we should be specifying and designing interactions when there is probably a difference between our hand positions and contact points when we are holding a device and tapping with the forefinger compared to holding a device in one hand and tapping with the thumb.

Are there any references that specify the difference between finger and thumb gesture or touch interaction patterns?

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I've had a thought about this in the past. First, consider a highly unscientific experiment I just did on myself (it doesn't have ethics board approval).

If I go to the home screen on my iPhone 5 and casually swipe upward from above the "dock" (a gesture with no assigned function), the result depends on how I'm holding the phone. If I use my thumb, swiping up consistently causes a sideways scroll-- moving one screen to the right if I use the right thumb, and one page to the left if I use my left thumb. If I use my finger, there's the same handed bias, but the magnitude is less-- it is only enough to cause a sideways scroll about one time out of five.

More research is called for but I would hypothesise that

  • a "loose" upward swipe will almost always lean toward the active hand

and

  • the sideways bias will be larger with a one-handed grip.

enter image description here

So, say your app always starts with a splash screen that must be swiped up to reveal the UI. Examining this one gesture, you could make a strong guess about how the phone is being held, and especially which hand is being used. The benefit of this is that (knowing the physical size of the screen), you can position controls within the "rainbow" of comfortable thumb gestures, and avoid the problem corners altogether. (The corner nearest the thumb is uncomfortable, and the farthest corner is difficult or impossible to reach with one hand).

Caveats: dynamic control positions can cause confusion. It'd be very important to check screen size. The splash screen (or whatever control you use for the test gesture) would have to encourage a loose, casual swipe-- if the user tries to swipe precisely at a single spot, the motion will be too controlled to provide the secondary clues.

  • Can you explain the meaning of the red numbers in the diagram? I am having trouble understanding it... – Michael Lai Jul 18 '14 at 1:03
  • Sorry, I made up the specific numbers! What I mean is that the over the course of the swipe gesture, the x-coordinate of the touch event will decrease for a left-handed swipe, and increase for a right-handed swipe; and, the amount of the increase / decrease will be larger for thumb gestures than finger gestures. The actual numbers would require more research. It could be that the variation between users is too great for the finger/thumb test to be reliable, but I believe the left/right test would work well. – bobtato Jul 18 '14 at 1:23
  • Nice diagrams (if you created them). It is a shame that the devices can't be designed based on the applications, but that the applications have to be designed based on the devices. Wonder what the interfaces would look like instead... – Michael Lai Jul 18 '14 at 2:05
  • Just wondering if you have had any further thoughts on this topic? I know it's been a while but I guess the question is still relevant. – Michael Lai May 24 '17 at 1:35
  • I'd actually completely forgotten about this! But (although I have never used it), I still like the idea of "finger forensics", where you get the user to perform a simple gesture and then analyse the exact path of the touch event to make inferences about what the most comfortable positions for UI elements are likely to be. – bobtato May 26 '17 at 1:06
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The design should be made in such a way that, it can perform equally well in both the case, i.e. user interacting with forefinger and user interacting with thumb.

Best way to do this is, to leave enough room surrounding any action elements, so that user would not tap on wrong buttons mistakenly.

enter image description here

Now when user controls with forefinger, his finger can easily move between a wide area of the screen. While they are controlling with thumb, its better to place key action elements in a projectile fashion.

Considering different user hold the phone differently, or same user holds the phone in different way depending on circumstances. enter image description here

Source and image credit

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    So nobody uses their phone with the left hand? That would invert the images, and thus it says that the only point you can always reach is the absolute center. – Hugo Delsing Jul 17 '14 at 9:59
  • There is no such screen-area as "not reachable"; But of-course there are some areas which may considered as "easy to reach". – S.M. Jul 17 '14 at 10:03
  • The top of the screen is always a hard to reach place, unless you use two hands and index finger. – Hugo Delsing Jul 17 '14 at 10:11

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