Psychophysics and user experience: Perceptual differences in the effort required to operate virtual push-buttons

Perceptual physical aspects of controls, such as interaction forces during operation, are important for ergonomic design. However, controls with equivalent physical properties may be perceived as functioning differently depending on their visual or acoustic appearance. To address this issue, the present study investigated how the size, brightness and loudness of pushbutton switches affect the perceived operating force. Two simple pushbuttons (standard and test) were presented side by side in a virtual environment and actuated with a 3D haptic device. The simulated mechanical properties of the pushbuttons (force-displacement characteristics) corresponded to those of real switch buttons. Three experiments were conducted with different groups of subjects. Physical characteristics of the standard button were kept constant and physical size, brightness and loudness of the test button were systematically varied respectively in all 3 experiments. Participants were instructed to press the standard and the test push-button one by one and to judge the perceived force for test push-button compared to the standard one in a 2-alternative-forced-choice task. Based on these judgments, the required operating force of the test key was adjusted using a simplified adaptive staircase procedure until the force of the test key varied by the point of subjective equality. Based on the subjective equality, the perceived operating force for the experimental condition was calculated. The results showed main effects of key size, brightness and loudness on perceived operating force. Consistent with findings from basic research (size-weight illusion), perceived operating force was higher for smaller keys. Additionally, perceived operating force was reported higher for higher brightness or higher loudness. Overall, the results suggest that psychophysical methods are suitable for objectively measuring the user experience of interacting with controls in application contexts.