CASE STUDY 1
When Usability Isn’t Enough: Enhancing the Sensory Quality of Product Controls1
Problem: The product, a consumer home appliance, had been through usability testing and participants had experienced no difficulties operating the appliance’s selector knob. After the test, however, several participants commented that they did not like the ‘feel’ of the selector knob. The engineering team was tasked with redesigning the knob to produce a ‘feel’ more similar to the knob on a comparison product that was better liked by participants. Upon examining the new knob, the team agreed that it felt more similar to the comparison knob, but were undecided whether the overall quality of its ‘feel’ was acceptable.
Approach: A technique called Perceptual Mapping was used to visualize the perceived similarities and differences among knobs. Perceptual Mapping consists of positioning knobs in a spatial configuration based upon the similarity judgments of a sample of users. Knobs judged to be similar are positioned near one another in space whereas knobs judged to be different are positioned farther apart. The chart below shows a two-dimensional perceptual map from a sample of thirty five participants. Nine knobs are shown including the Comparison knob, the original prototype (Prototype 1), four new prototypes created by engineering to span a broader range of detent torque and sound qualities (Prototypes 2-5) and three knobs from other production products. Participants also rated the pleasantness of each knob and the most pleasing knobs are shown with outline symbols in the Perceptual Map. The engineering team also provided torque measurements on each knob. The arrow that has been overlaid on the map shows the direction of increase in one property of torque, the difference between maximum and minimum detent torque, which was found to be correlated with the positioning of knobs in the perceptual map. Knobs positioned at the extreme left side of the Perceptual Map, therefore, have the smallest difference in detent torques and the most subtle feeling detents. Knobs at the extreme right side of the Perceptual Map have the largest difference between detent torques and the most distinct feeling detents.
The first thing to note is that the Comparison knob and Prototype 1 are positioned near one another in the perceptual map indicating that the engineering team was successful in creating a similar ‘feel’. Prototype 1, however, was not rated by participants to be pleasing whereas the Comparison knob was. Therefore, Prototype 1 is probably still not a good choice for the product. Prototypes 3, 4 and 5 at the far right of the Perceptual Map are perceived to be very different from the Comparison knob, but were rated by participants to be pleasing.
This pattern reveals that participants attended to two different properties of knobs when making their similarity comparisons. One is reflected in the difference between knobs on the left side of the perceptual map, which have subtle feeling detents, and knobs on the right side of the perceptual map, which have distinct feeling detents. The other property influences pleasantness, but is unrelated to tactile feel.
A comparison of Production knobs A and C at the top and bottom of the perceptual map is helpful in identifying this property. Some participants commented that the detents for knob A seemed too loud whereas the detents for knob C seemed too muffled. This suggests that differences among knobs in the vertical dimension of the Perceptual Map reflect differences in detent sound. The most pleasing knobs are positioned between the two extremes suggesting that a medium level of detent sound is optimal. Prototype 1 is positioned nearer knob C at the bottom of the perceptual map suggesting that the sound of its detents is unpleasantly weak.
Based upon these results, the team chose Prototype 3 for the product because it had both a pleasing sound as well as a distinct tactile quality that differentiated it from the Comparison product. The quality of a distinct tactile feel aligned better with the product’s robust brand image. Perceptual Mapping, therefore, not only helped the team to determine that Prototype 1 was not acceptable, but helped identify a more appropriate tactile feel that was better suited to the product’s brand image.
1Based upon research reported in: Kleiss, J. A. (2008). Sensory quality evaluation of clothes washing machine selector knobs. Proceedings of the Human Factors and Ergonomics Society 52nd Annual Meeting. pp. 1687-1691.