Why you think your phone is vibrating when it is not

Most of us experience false alarms with phones, and as Tom Stafford explains this happens because it is a common and unavoidable part of healthy brain function.

Sensing phantom phone vibrations is a strangely common experience. Around 80% of us have imagined a phone vibrating in our pockets when it’s actually completely still. Almost 30% of us have also heard non-existent ringing. Are these hallucinations ominous signs of impending madness caused by digital culture?

Not at all. In fact, phantom vibrations and ringing illustrate a fundamental principle in psychology.

You are an example of a perceptual system, just like a fire alarm, an automatic door, or a daffodil bulb that must decide when spring has truly started. Your brain has to make a perceptual judgment about whether the phone in your pocket is really vibrating. And, analogous to a daffodil bulb on a warm February morning, it has to decide whether the incoming signals from the skin near your pocket indicate a true change in the world.

Psychologists use a concept called Signal Detection Theory to guide their thinking about the problem of perceptual judgments. Working though the example of phone vibrations, we can see how this theory explains why they are a common and unavoidable part of healthy mental function.

When your phone is in your pocket, the world is in one of two possible states: the phone is either ringing or not. You also have two possible states of mind: the judgment that the phone is ringing, or the judgment that it isn’t. Obviously you’d like to match these states in the correct way. True vibrations should go with “it’s ringing”, and no vibrations should go with “it’s not ringing”. Signal detection theory calls these faithful matches a “hit” and a “correct rejection”, respectively.

But there are two other possible combinations: you could mismatch true vibrations with “it’s not ringing” (a “miss”); or mismatch the absence of vibrations with “it’s ringing” (a “false alarm”). This second kind of mismatch is what’s going on when you imagine a phantom phone vibration.

For situations where easy judgments can be made, such as deciding if someone says your name in a quiet room, you will probably make perfect matches every time. But when judgments are more difficult – if you have to decide whether someone says your name in a noisy room, or have to evaluate something you’re not skilled at – mismatches will occasionally happen. And these mistakes will be either misses or false alarms.

Alarm ring

Signal detection theory tells us that there are two ways of changing the rate of mismatches. The best way is to alter your sensitivity to the thing you are trying to detect. This would mean setting your phone to a stronger vibration, or maybe placing your phone next to a more sensitive part of your body. (Don’t do both or people will look at you funny.) The second option is to shift your bias so that you are more or less likely to conclude “it’s ringing”, regardless of whether it really is.

Of course, there’s a trade-off to be made. If you don’t mind making more false alarms, you can avoid making so many misses. In other words, you can make sure that you always notice when your phone is ringing, but only at the cost of experiencing more phantom vibrations.

These two features of a perceiving system – sensitivity and bias – are always present and independent of each other. The more sensitive a system is the better, because it is more able to discriminate between true states of the world. But bias doesn’t have an obvious optimum. The appropriate level of bias depends on the relative costs and benefits of different matches and mismatches.

What does that mean in terms of your phone? We can assume that people like to notice when their phone is ringing, and that most people hate missing a call. This means their perceptual systems have adjusted their bias to a level that makes misses unlikely. The unavoidable cost is a raised likelihood of false alarms – of phantom phone vibrations. Sure enough, the same study that reported phantom phone vibrations among nearly 80% of the population also found that these types of mismatches were particularly common among people who scored highest on a novelty-seeking personality test. These people place the highest cost on missing an exciting call.

The trade-off between false alarms and misses also explains why we all have to put up with fire alarms going off when there isn’t a fire. It isn’t that the alarms are badly designed, but rather that they are very sensitive to smoke and heat – and biased to avoid missing a real fire at all costs. The outcome is a rise in the number of false alarms. These are inconvenient, but nowhere near as inconvenient as burning to death in your bed or office. The alarms are designed to err on the side of caution.

All perception is made up of information from the world and biases we have adjusted from experience. Feeling a phantom phone vibration isn’t some kind of pathological hallucination. It simply reflects our near-perfect perceptual systems trying their best in an uncertain and noisy world.

This article was originally published on BBC Future. The original is here.

8 thoughts on “Why you think your phone is vibrating when it is not”

  1. Ah! It was *your* article I referred to in my blogpost on ‘the human behind the notification stress’ last Friday 😉 Cheers!

    However, The One Question that I was left with after reading is: what can explain for the fact that different smartphone owners have developed different biases? That smartphone owner number 1
    experiences false alarms frequently and smartphone owner number 2 rarely does, or not at all?

    Don’t these interpersonal differences imply that there is more involved in phantom vibrations than just that ‘common and unavoidable’ brain function?

    1. The same trade off (false alarms vs misses) occurs in all people, but a myriad of factors will shift the bias around. An important one is, presumably, the cost each individual puts on missing a genuine call. The higher the cost, the more false alarms, I predict.

      1. Agreed, Tom.

        Furthermore, the cost an individual puts on missing a genuine call (aka ‘missing an emotional stimulus’) seems to be associated with ‘novelty seeking’, the personality trait associated with a variety of dopamine sensitive brain regions in the medial prefrontal cortex. (http://t.co/uB188hOqnF)

        Which other factors do you think play a role in shifting the bias?

  2. Forget about false fire alarms and phantom phone vibrations. Ask any new parent. My spouse and I often hear phantom cries from our napping infant when we’re busy with other tasks. Happily, about half the times we go running to check on the baby he is still fast asleep.

  3. Interesting, I think the effect of a napping infant on a new parent might bear resemblance to the effect of a smartphone on its user. They both seem to afford a major mental sensitivity.

  4. but why you actually have the false hearing/feeling of the vibration/ringtone/cry ( i understand the false belief, but what about the actual ring that you think you hear) ? In other words, when your brain decides that it is going to make the conclusion (falsely) that “it’s ringing”, do you actually hear the ring because the networks of neurons that usually fire when your phone is actually ringing (including neurons linked to your auditory perception) will also still fire?

    1. Absolutely, yes, the same neurons that feel a real phone ring are active. The decision maker in this case is not some slow deliberative conscious experience – it is not you thinking to yourself “is that my phone ringing?”. It is the automatic mind-brain machinery which delivers a report to your conscious experience. It is this machinery which makes the false alarm – miss trade-off, so when it makes a mistake it feels exactly the same (and activates the same sensory machinery, I predict) as a true ring.

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