An experiment was conducted to investigate the affect that sound would have on the interaction with on-screen buttons in a mobile computing device. Sixteen participants from the Computing Science Department at Glasgow were used. The selection was made up of postgraduate and undergraduate students and staff, nine male and seven female, all between the ages of 21 and 45.
The experiment used a fully counterbalanced, two-condition, within-groups design. The independent variables were button size and sound type. There were two conditions: standard (16×16 pixels) and small (8×8 pixels) buttons (see Figure 1). Both of these sizes are commonly found on PDAs. There were two 7- minute treatments in each condition: visual only buttons and visual plus sound.
The experiment was run on a 3Com PalmIII handheld computer with input via a stylus. The task the participants had to perform was similar to that of Brewster et al. ( 1995). Participants had to enter a series of five digit strings (shown in the target window in Figure 1) using the numeric keypad. After each digit had been tapped the OK button had to be pressed to confirm it. The numbers appeared in the window labelled 'Current'.
The dependent variables were subjective workload (using the standard NASA TLX workload test) and number of strings entered. Together these gave a good quantitative and qualitative measure of usability. Training was given before each part of the experiment began and NASA TLX workload scales were completed after each treatment.
The main hypotheses were: