ZULQUERNAIN MALLICK AJE Vol.9 2009 19-32
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most have not been properly evaluated using either theoretically or empirically. Several factors may affect user performance when using VDUs for data entry or
to search for items on the screen. These factors include vibration, the color of the text and the background, and user age. Therefore, these factors must be considered
when designing devices for use in mobile settings. The colours of the text and of the background textbackground on a display
affect user performance, especially in desktop and lap-top type computing systems. The textbackground colours on a display affect user performance, especially in
desktop and lap-top type computing systems. Users prefer a high contrast between text and background colour Ling and Shaik 2002. Appropriately-chosen colours
can also help convey information quickly. The readability of text increases with luminance contrast between the text and background colors Shieh and Lin 2002
and users can find targets more quickly as color difference between the text and background increases Wang et al. 2002. Normally, mobile computing is done
during the day time; sunlight may cause glare, so a dark background and white text may be the best option.
Older people enter data more slowly than middle-aged and younger people Khan 2002. People of different ages use computing systems in mobile
environments, so possible age-related effects on task completion should be assessed, but little work has been done to do so. In tasks that require divided attention,
performance of the task involved was significantly affected by age Salthouse, 1982; Kaulser 1982. Younger subjects perform better than older subjects Burke et al.
1980, and the time required to allocate attention increases with age Madden 1992. The objective of this study was to quantify the combined effects of vibration, colour
of text and background, and user age on users’ accuracy while entering data in a mobile environment.
2. Methods
2.1. Subjects
Forty-two male subjects’ different ages participated in this study; all had normal vision either with or without the aid of glasses, and none had any history of
neuromuscular disorders. The subjects chosen had almost the same amount of experience with working on lap-computers in a stationary zero-vibration
environment. The subjects selected were divided into three groups: 18-32, 33-47 and 48-62 years old. Each group included 14 subjects. Users’ input speed was measured
as the number of characters entered per minute without spaces NCEPMWS; to avoid any temporal effect that might affect subjects’ performance, data were
recorded at approximately the same time of day throughout the experiment.
2.2. Stimuli and experimental task
A lap-top computer Armada 1500, Compaq was employed in all experiments.
Data entry task in mobile computing: effects of vibration, display colour, and user age
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The sensor of the vibration level meter was kept at a specially designed platform which did not affect the impact of vibration and the display was kept in front of the
experimenter to allow him to constantly monitor the level of vibration. The mean value of the angle between eye level and the centre of the screen of
the lap-top for all the subjects was kept at approximately 15° SD = 3.16°. The temperature of the vehicle was maintained at approximately 26 ± 3 °C. While
performing the experimental task the level of vibration in the driving environment was kept at a specified value by constantly monitoring the level of vibration in the x,
y and z directions and running the vehicle at the appropriate speed.
Before the actual experiment in the test vehicle, a trial session was arranged; this was done for two purposes. The first purpose was to familiarize the subjects
with the experimental procedure; the second was to determine the reaction of the subject in connection with the recorded text input in the audio-cassette that was
replayed during the experimental session. Subjects did not adapt easily to this style of stimulus presentation style; therefore one experimenter sat beside of the subject
and read the text to be entered. Out of 42 subjects 32 preferred this style of stimulus presentation but requested slow speed reading so that the text entry task could be
completed without difficulty. Subjects were required to sit on the vehicle seat without back rest with the two hands on the keyboard as was observed to be the
practice of the end-users while working on VDUs .Before performing the experimental task data entry, the subject sat in the vehicle at a prespecified level of
vibration for 60 minute and then the stimulus was presented to him. Each text entry task required 10 minutes. After completion of the task at each level of vibration
separately, the content entered was saved with the name of the subject and later downloaded later to check it for errors. Subjects were allowed to rest for 30 min
between successive trials; during this period they were isolated from the driving environment. Two textbackground color employed in this experiment: black
characters on white background and white characters on black background. The experimental task was repeated for both textbackground colour combinations.
2.3. Experimental Set-up
Experimental investigations were carried out in a real life driving environment on a passenger car Waja manufactured in Malaysia. This particular type of car was
chosen because ~ 65 of Malaysian people use this car. This car has a 1597-cc S4PH 4- cylinder 16-valve DOHC engine that has a maximum power of 82 kW at 6000 rpm,
a maximum torque of 148 Nm at 4000 rpm, and a multi-point fuel injection system. The bore of this engine is 76.0 mm and its stroke is 88.0 mm. The front suspension
uses a MacPherson strut with a stabilizer bar; the rear suspension uses Multilink with stabilizer bar. The car is 4465 mm long, 1740 mm wide, 1420 mm high and has
a wheelbase of 2600 mm. Its maximum speed is 190 kmh.
The experimental setup Figure 1 was comprised several sub-systems: a vibration level meter Bruel Kjaer Deltatron, Type 4504, a 12-volt battery for
energizing the amplifier Bruel Kjaer, Type 2260, a digital lap-top Armoda 1500 Compaq.
