My amplifier broke two weeks ago. It was intermittently cutting off the sound to the right speaker. When I jiggled the speaker cable at the right speaker output port on the amp, the sound usually came back. Therefore, my logical conclusion was that the output port was broken. I tried fixing the problem by cleaning the amplifier (after 9 years, there was a fair amount of dust built up inside), however this did not remedy the problem.

So, I bought a new (second hand) amplifier. Incidentally, it turns out to be much better than the one I used to have, even though that was a good one to begin with. And the problem was fixed. I rejoiced and spent quite some time annoying the neighbors with a much richer sound system. Until it broke again…

Now, as the title suggests, there’s a reason here for me to mention mental models. It is a phenomenon used to describe a person’s understanding of something, as a mental representation. For example, if you flip a light switch, the light turns on. Therefore, your mental model would entail something like ‘the light switch acts as a gate for electricity to flow towards the light bulb’. If you flip the switch, and nothing happens, you might conclude that the light bulb is broken. Upon replacing the bulb with a new one, the light switch once more turns the lamp on and off, and you update your mental model with this information: ‘when the switch is flipped, and the light doesn’t come on, the lamp is probably broken’.

My mental model of my previous amplifier is a good example of a model being wrong. Whenever the sound was not reaching the right speaker and whenever I jiggled the speaker cable, most of the time the sound would come on again. Therefore, my mental model was reinforced with the ‘fact’ that jiggling the cable, which in turn led me to believe the contact between the cable and the output port was impaired, ‘fixed’ the problem. My solution, to buy a new amp was therefore correct. However, my mental model was not: after buying the new amp, the problem returned. It would seem that the sound returning only coincided with the jiggling of the cables. This led to a faulty mental model. Now, sleep won’t be lost over this, on the contrary: I’ve got a sweet new (old) amp.

However, in 1989 there was a plane that crashed near Kegworth (Leicestershire, UK), because of a similar faulty mental model of the pilots. The story there was, that one of the engines broke down, causing a vibration throughout the plane. The pilots identified the engine responsible and turned it off and at that exact same moment, the vibration stopped. However, it turned out that they were wrong, and when they realized the wrong engine was turned off, it was already too late. The result was the tragic loss of 47 lives (Besnard, Greathead & Baxter, 2004). For a complete account of this crash, and the influence mental models may have had, I suggest you read the article at the bottom of this post, it is not too difficult a read.

Anyway, I tried everything to fix the problem that didn’t include me unnecessarily buying more stuff: switching cables, changing cables, replacing parts in the entire system where I could, reinstalling/updating audio drivers. But nothing worked. I eventually brought the amp and the speaker to the store where I bought both the amp and the speakers, to see if they could find the problem. They could not. The problem couldn’t even be reproduced in the store (and not from lack of trying). In the mean time, the missus’ miniset we had hooked up to the pc started displaying the same problem. So, that left us with only one possible solution, replace the cable between pc and amp.

So far it works fine. Let us hope it stays this way… In any case, I believe this to be a good illustration of how a faulty mental model can cause incorrect decisions based on your perceptions. So the next time, something is not working as it should, remember your mental representation might not be entirely accurate. Additionally, I really should’ve headed the advice given by my instructor to become an audio technician, a course I once had: ‘when there’s something wrong with the sound, ALWAYS check the cables first. In 99% of all cases, the problem lies there’. He was right again…

References:
Besnard, D., Greathead, D., & Baxter, G. (2004). When mental models go wrong: co-occurrences in dynamic, critical systems. International Journal of Human-Computer Studies 60, pp. 117-128.