Home > Human Factors history and studies > Improvement of soft touch displays

Improvement of soft touch displays

I do not have the latest smart phone – just an old HTC, but it is enough for me. However beside the nice design and enlarged display which I really like I miss the old keys. Typing was much easier with old phones. Enlarging the virtual keyboard rotating the phone does not really help. The keys cannot be felt with the fingertips and the size of the fingertip covers the keys (usually a bit more than one). Interaction feels a bit like a blind flight. It gets better while practising, the brain learns the position of the letters but does not lead to an as good typing speed as with haptic feedback: The lack of haptic feedback is critical for user as there is no feedback given about the location of touch. It could be that the originally indented position of the touch is missed. This missing feedback leads to typing errors. Following methods are used to mitigate errors:

  • Highlight keys likely to be used next (e.g.: colour, bolding, size)
  • Make the keys larger or smaller dependent on their likelihood of being used
  • Resizing of target areas instead of keys themselves
  • Other help is of course a stylus (but here with focus on precautions to avoid loss)
  • Other help not discussed here is to decrease typing through intelligent suggestions

Dynamically resized key areas, according to their probability of use, help the interaction in most cases but they shall not hinder the user from typing (e.g. uncommonly typed names or places). The figures below show an example for this case. According to the probability the touch target area for the “s” is enlarged so it nearly completely overlaps the touch area of the “e”.

soft keys touch target

White paper Microsoft: soft touch displays improvement of the target area

The negative effects are avoidable with definition of minimal available touch target areas for each key. Enlarged key areas do not overlap other keys. A defined area of each key is always touchable. A white paper from Microsoft includes research showing an improvement of typing speed and less typing areas in interfaces following this design rule. Important is to define the smallest touch target area considering two effects: first, the probability of the next letter and second, the touch pattern of the user (target area the user prefers).

Specifically the area for presenting information on a mobile phone screen needs to be defined with precisely. Better leave a little “edge”. With my old HTC I have some problems to activate the keys presented on the edge of the touch screen. It seems those keys require more force for activation compared to other keys, it feels like pressing beside instead of the edge of the touch screen.

Future research: What is the ideal size of the touch target area? People have different sized hands. Currently there are different suggestions dependent on the supplier: Apple suggests an area of 44x44px (What does it mean dependent on the resolution?), Nokia an area of 7x7mm for finger usage / 8x8mm for thumb usage and Microsoft an area of 9x9mm preferred and 7x7mm only if space is very restricted.

How do the finger touch points dependent on the user’s hand size and how can the user interface adapt?

Source: “Usability guided key-target resizing for soft keyboards”  Asela Gunawardana, Tim Pack, Christopher Meek; White paper Microsoft

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