Mobile Evolution As you know, in the past two decades we have witness an evolution in mobile devices
That is leading us to touch interfaces. These stylish devices are replacing traditional keypads in mobile phones and provide a more
a more engaging and pleasantness user experience and promise to be more effective and efficient than their predecessors
However, these devices lost an important feature, their tactile feedback, thus
one may argue that touch interfaces lost the physical stability provided by their button-based counterparts. Indeed, these devices are highly physical demanding
Due to the absence of tactile affordances, touch screens make it harder for people to accurately select targets
This problem occurs to everyone, particularly when situational impaired due to tremor. For instance, when you are walking ou in a bus
But also with motor disabled users who suffer from lack of precision when moving their upper limbs.
On the other hand, touch screens also presents as a good opportunity for motor disabled people, since they are less demanding than keypads, regarding the strengh required to select a target.
Also these interfaces can adapt themselves to their users, making it possible to design interfaces that fit the users’ capabilities
In fact, there have been successful efforts to improve access to mobile touch screens. Examples include EdgeWrite or Barrier Pointing. Both techniques take advantage of the remaining physical properties of these devices, the edges.
The challenge is to understand how tetraplegic people use touch screens and to find a way to build better touch interfaces. Our goal with this work is to provide this knowlage … However, there is no compreensible knowledge how to build better touch interfaces. Therefore, we believe that a step back is required in order to fill this gap
To overcome this we have performed extensive user evaluations with 15 tetraplegic people
And explored several screen areas such as corners
and edges, because these two areas are usually used to provide additional physical support to the users. Examples of previous works include edgewrite or barrier ponting
And explored several screen areas such as corners, and edges
and also exploring target characteristics, as their size
The first interaction technique was tapping. T his is the most used technique in current touch screen devices. We just need to touch in order to select a target. This could be done in the middle areas, corners or edges.
In the second technique users had to cross the target in order to select it. This was performed in the middle areas
Exiting was similar to Crossing, but a selection was acknowledged by performing a gesture towards the screen edge or corner and crossing the intended target
Gesturing was the only technique that did not require a target selection. Users could perform directional gestures anywhere on the device’s surface
We recruited 15 tetraplegic participants (two females, thirteen males) averaging 42 years old, from a physical rehabilitation center. All participants had some residual arm movement. All user possessed a mobile phone, but most never experienced with a touch screen before
I have described to you all experience, However, in this paper we have only looked at a particular method and thus, on a subset of the described experience, which is tapping. Also we were particularly interested in accuracy rates.
First of all, we want to see if target size had influence on task errors. This was our hypothesis
As we can see here accuracy increases with target size reaching a 20% error rate. There was a significant effect on Task Errors between the small and both medium and larger sizes. These results indicate 12 mm as an approximate suitable value, since there was no significant differences between the two largest sizes. Therefore, for UI designers this may be a good commitment between error rate and required space. However, participants still had a 20% error rate which is significantly high.
We can reject our hypothesis and conclude that target size has influence on task errors
Regarding corners, the lack of control in users’ movements suggests that additional support may improve their performance. We tested whether taping a target in the corner of the screen is indeed easir than tapping a target in any other position.
These are the results for all sizes, and we found no significant effect of target position on task errors. Only a minor effect was found on the smallest size, with less errors in the corners.
Therefore corner targets do not influence error rates
Regarding edge targets we did a similar analysis
And, again, we could not find any significant difference on task errors between tapping on the edge or not.
So, we have this .. However,
we did found an interesting interaction between the preferred arm and the error rate on a specific edge for medium and largest size. Results indicate that targets near the users support, or preferred hand are easier to tap.
For vertical areas we divided the screen vertically in 3 areas, top, center and bottom and tested our hypothesis
and we found a significant difference in both medium and largest sizes, with the bottom areas being easier to select.
Thus, vertical areas influence task errors
The most relevant implication suggested by these evaluations is that motor disabled users can operate devices with different success rates depending on screen position. While able bodied people can easily adjust the device to their convenience, tetraplegic users have less freedom to interact with the device
As for size, results showed that error rates start to level off above 12 mm, which indicates that a good target size would be around this value.
Error rates are still high when compared to previous reports of able bodied users performance even when situationally impaired being around 10%
Concerning target positioning, it is easier to select targets near users’ support or preferred hand. One limitation of this evaluation was the small number of left-handed users, which limits our conclusions on target locations on the screen, a particular good corner or good edge for each hand
In the future, we will analyze more interaction techniques and the relationships between them. We will also analyze the differences between tetraplegics and able-bodied people in greater depth, in order to understand where they diverge and identify where extra attention is required when designing touch interfaces.
Assessing mobile touch interfaces for tetraplegics
Assessing Mobile Touch Interfaces for Tetraplegics Tiago Guerreiro Hugo Nicolau Joaquim Jorge Daniel Gonçalves