Car Radio

Problem Description

Get in the car. Start it up. Turn on the radio. No sound? It's probably just turned down too low. I'll turn it up a bit. AAAAHHH! That was far too loud. Turn it down. Now where did that station go?

HCI Analysis

A car radio.

This radio looks fairly simple, and its simplicity is its major flaw. Even though there are few controls, and the controls have fairly intuitive functions, feedback is minimal.

Since the radio is old, it has become a bit temperamental. From time to time, the sound goes out altogether. When a new user gets into the car, and hears no sound from the radio, there are three possible interpretations:

  1. The radio is turned off.
  2. The volume is turned all the way down.
  3. The sound has gone out again.
Since the radio provides very little feedback on possibility 1 (whether the power switch is depressed), no feedback on possibility 2, and can't be expected to provide feedback on possibility 3, the user must guess the cause of the problem.

Given that the user can't directly determine the state of the system, forming a goal about changing to a desired state is extremely difficult (Norman, 1988). This can cause problems if the sound has gone out, and comes back on while the user is adjusting the volume knob.

There are only four buttons for preset stations. To increase this functionality, the user can press two station buttons at a time, which is interpreted as a "virtual" button. There are three virtual buttons, represented by the combinations of buttons 1 and 2, 2 and 3, and 3 and 4.

This virtual button feature has extremely low learnability, since people seldom read the manual for a car radio. It also has relatively low memorability. Users don't often use the virtual buttons because they set their most frequently-used stations on the "actual" buttons, and seldom listend to the stations set on the virtual buttons. Adding to this non-use is the fact that the virtual buttons are difficult to press. To press a virtual button using two fingers takes accurate timing, while pressing a virtual button with one finger takes accurate movement (Card and Moran, 1986).

Recommendation

The radio designers need to take Apple's (1992) advice and provide better feedback. When driving, a user needs to be able to rapidly determine the state of the system. Lights indicating whether the power is on are needed. An indicator is needed on the volume knob, or a scale on the display panel to indicate current volume setting.

There should be more channel preset buttons, so that there is not a need to make them do double-duty. Driving is difficult enough without attempting to push two buttons at the same time, just to change the radio station. Fortunately, newer radios seem to have abandoned this poor design technique.

References

Apple Computer (1992) Macintosh Human Interface Guidlines. Addison Wesley. [Chapter 1]

Card, S. and Moran, T. (1986) User Technology: From pointing to pondering. in Proc. ACM conf. on History of Personal Workstations, Palo Alto. ACM.

Norman, D. (1988) The Psychology of Everyday Things. New York: Basic Books [Chapter 2]

rscherle@cs.indiana.edu
Last modified: Fri Mar 26 16:55:49 EST 1999