When performing the text editing task with the TrackPad(tm), during the training session, the subjects had
already achieved a performance equivalent to 65% of mouse performance. A performance of more than
90% was achieved after two hours and 100% in the fifth hour session. This means that the learning period
for such tasks will in practice be accomplished within one working day. The average performance achieved
with the TrackPad(tm) for the eight tasks with Fitts�s Test, during the last session, was lower than that with
the mouse, but the difference was not statistically significant.
The results of this study indicate that the TrackPad(tm) can be used for everyday tasks without causing
postural discomfort or fatigue. In some respects, this device may even be preferable to the mouse, if the
users can achieve the same level of performance.
Keywords:
Input device, TrackPad(tm), postural discomfort, EMG
POSTER CONTENTS
The poster serves discussing following items:
- The objectives of the study
- The questions the research work should help answering
- The methods used
- The test procedure
- Main results of the research work.
In addition, some of the important results are represented for discussion.
The objectives of the study
Performance and precision
Although the main focus of the study was postural comfort and biomechanical load, the level of
performance and precision the subjects achieved under test conditions is of importance since an input
device has to be task adequate.
Biomechanical load
The assessment of the biomechanical load of the arm muscles is needed to evaluate the likelihood of
causing discomfort or strain.
General comfort
The impact of the use of the device on general comfort (e.g. self-reported fatigue or stress) is a good
indicator for effects that cannot be assessed by measuring the biomechanical load.
Postural discomfort
Postural discomfort at different parts of the body is another good indicator for the overall impact of the use
of the device on the subjects.
Methods
Performance Test
The performance was measured by a text editing task and eight Fitts�s Test with two levels of task difficulty
corresponding to the intended use of the TrackPad(tm). The results were compared with those achieved with a
mouse, a device for which the average experience of the subjects was longer than 3 years.
EMG-measurements
For part of the assessment of the biomechanical load, EMG-measurements of the muscles involved in the
operation of the TrackPad(tm) were performed.
Posture analysis
The posture of the arm and the hand (pronation, ulnar deviation etc.) was assessed using video recordings.
Questionnaires
The subjects evaluated their general comfort, postural comfort, and stress/strain with questionnaires which
had been tested in various studies.
QUESTIONS
The study was designed to answer following questions:
- Is the device suitable for the tasks for which the specific computer was designed?
- Is there undue biomechanical load associated with the use of the device?
- Are there indications that the use of the device is associated with fatigue?
- Is postural discomfort affected negatively if the device and the computer are used for normal office
tasks?
- Are there indications for undue stress?
MAIN RESULTS
Performance (Speed and Errors)
When performing the text editing task with the TrackPad(tm), during the training session, the subjects had
already achieved a performance equivalent to 65% of mouse performance. A performance of more than
90% after about two hours and 100% in the fifth hour session. This means that the learning period for such
tasks will in practice be accomplished within one working day. This was the most encouraging outcome of
the test since this test task resembled the most important use of the device.
In the Fitts�s Test, the errors of the subjects occurred only sporadically and could therefore not be analysed.
Since this was true for the entire test from the training session until the end, the performance of the subjects
with respect to accuracy was at an adequate level in all sessions.
With regard to speed, the performance was direction dependent. The average performance over all eight
tasks during the final session was lower than that with the mouse, but the difference was not statistically
significant. However, the performance in the vertical direction (moving the cursor on a vertical line)
remained remarkably low after five hours of testing (less than 80% of mouse performance). This means that
the learning period for pointing tasks will be longer than one day if the same level as with the mouse is to be
achieved.
Surprisingly, the difference of TrackPad(tm) to mouse performance was smaller for the tasks which had a
higher level of difficulty. Both the subjects and the experimenters tended to underestimate the level of
precision that was achieved with the TrackPad(tm).
Postural Comfort and General Comfort
It is believed that prolonged working with constrained postures is likely to cause postural discomfort or
fatigue. The degree to which unfavorable effects occur after a certain time period depends upon how
inconvenient the posture is. Recent research has demonstrated that within a four hour test period, of
performing computer tasks, levels of discomfort increase even for those parts of the body not involved with
the operation of the specific device [2].
Both direct ratings of postural comfort (wrists, forearms, back region) and ratings of fatigue and related
symptoms (e.g. headaches, back aches, neck aches) gave no indication of discomfort or fatigue related
symptoms after five hours of work. In comparison to a four hour keyboard test, conducted under similar
conditions, the results obtained from the questionnaires of the TrackPad(tm) study were significantly better.
Instead of increasing, most indicators for postural discomfort showed a decrease.
Biomechanical load
The analyses of the EMG-measurements yielded no indication for progressive fatigue or increased
muscular load from one session to the next. On the contrary, the recorded levels showed a decrease in
muscular activity. This may have been caused partly by learning effects. Surprisingly, the impact of the task
difficulty on the muscular load was not significant.
The postural analyses indicated that undue deviation, extension, or flexion of the hands, which may cause
discomfort, generally did not occur. The average values were within the limits supported by the physiology
of the human arm. However, personal preferences of arm posture were substantially different. Thus, some
users may perceive discomfort due to the hand position they choose. This is not a design flaw but simply a
matter of user education
Interestingly, the hand deviation (bending the wrist towards the little finger) of the subjects using the mouse
was greater than those using the TrackPad(tm) (18 versus 11.3 ). The average hand deviation angle with the
mouse was almost the same as in a recent Swedish study (18 versus 17.6 , [1]). From this point of view,
the TrackPad even seems to be preferable to the mouse.
Discussion
The results of this study indicate that the TrackPad(tm) can be used for everyday computing input tasks
without causing postural discomfort or fatigue. In some respects, this device may even be preferable to the
mouse, if the users can achieve the same level of performance. With respect to the levels of accuracy
required during the test, a sufficiently high performance of the subjects was observed from the beginning.
For some tasks, it only took the subjects five hours to become as proficient with the TrackPad(tm) as that
achieved with the mouse after many years of mouse experience. Given the fact that the test was not
designed to exploit the features of the software for optimal learning progression, this is a very positive
indication. In practice, the users can select the appropriate control/display ratio to their preference and
change it as they become more proficient
For other tasks, the learning period may be longer than one day. However, it should be kept in mind that
users of other input devices also need a lengthy period of familiarization that may even last longer than
observed in this test.
In this study, the TrackPad(tm) was not tested for tasks which require very high accuracy (e.g. CAD-tasks,
manipulation of graphics etc.). The reason for this was the manufacturer�s intention of utilizing the device
for a portable computer. Provided that further studies confirm our assumption that even higher levels of
accuracy can be achieved, the TrackPad(tm) can be utilized in different types of devices to the benefit of the
users, especially in work environments with space constraints.
References
1. Karlqvist, L.: Variation in upper limb posture and movement during word processing with and without
mouse use, ERGONOMICS, 1994, Vol. 37, No. 7, 1261-1267
2. Karwowski, W.; Ray, E.; Salvendy, G.; Noland, S.: The effects of computer interface design on human
postural dynamics, ERGONOMICS, 1994, Vol. 37, No. 4, 703-724
