Wait for it…

Improving the usability of an interface, by making it do more or less what the user actually expects of it, is a pretty good route to an overall sound user experience. Yet, there’s one key mistake almost every interface I’ve looked at makes in this regard – what I call the Spurious Stimulus Response. That is…

responding to user input in the context of stimuli they haven’t been given the time to acknowledge.

For example, consider a dialog box, suddenly appearing centre-stage in an interface, as the result of an incoming message, error condition, or some such situation. If the user was to click on it, or press a key, within 250 milliseconds of it appearing, then they are not reacting to its appearance – instead they were probably intending to action something else.

In an interface without a pointing device, such as on TV, using a traditional remote control, the problem is exacerbated, since the user only need press OK to commit whatever action happens to come into focus. When using an infra-red remote control, this problem is compounded further, because it usually takes a fraction of a second for the receiving device to recognise the incoming IR pulses as something it needs to deal with and push that signal up through the software stack to the UI layer.

I suggest employing a simple fix, which draws its inspiration from the behaviour of nerve stimulation – called the refractory period. That is…


to render a control inactionable, after a change in UI state, long enough for the user to assimilate said state change.

The few interfaces which loosely employ some such technique, do so usually just as a side-effect of having some animated transition when a dialog appears, for example. Sometimes, a button or other control is disabled until the transition completes. This is actually a very good way of ‘easing the user into’ the change in UI state – but a refractory period should still be implemented where animation is absent.

The refractory period could be some function of the amount/importance of information provided. A good example of this is the Firefox Add-on confirmation dialog, which forces you to wait a few seconds, rather than letting you mash RETURN and install some random plugin.

But, in its most simple incarnation, a refractory period may simply be used to filter out double-click mania. Please start designing this kind of behaviour into your UIs – your users will thank you.

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