The rule of thumb floating around when I was working on physical input devices last was to keep latency under 50ms so people wouldn't get frustrated. I don't have any sources but it becomes a bit more obvious when you look at it as fractions of seconds and then compare that to how slowly seconds actually tick by on a clock.
I remember Dan posting that he typed at ~120wpm somewhere. 120wpm is 0.002 words per ms or 0.4 words per 200ms. Wouldn't one notice if they're almost halfway through a word and nothing has shown up on the screen?
Even for certain applications, 50ms is quite a lot. When using MIDI devices and playing piano over the computer, I certainly notice anything above 20ms.
We may be slow to react to sudden events, but we are very good at noticing the lag for predictive events (keyboard typing, piano playing, ...).
Martin Molin of the Wintergatan fame recently posted some experiments regarding latency on his YouTube channel[0]. From watching those videos it becomes quite obvious that your statement is definitely correct.
Yeah this rule of thumb was for low fidelity things like hand radio buttons.
> We may be slow to react to sudden events, but we are very good at noticing the lag for predictive events (keyboard typing, piano playing, ...).
It does make sense in my lay person’s understanding that the chain of eye -> brain -> hand for reactive events would be slower than brain —> eye + hand for proactive events.
> Wouldn't one notice if they're almost halfway through a word and nothing has shown up on the screen?
There is quite a delay between the eye detecting something and it being consciously processed to the point of being used in decision making. Away from built-in reactions (move hand away from burning sensation and so forth) that are not consciously controlled there is a sometimes surprising amount of latency in our view of the world. It is surprising because the brain does a rather good job of smoothing it out with guesses/predictions such that you generally don't notice.
Only when things fall outside the range of patterns you naturally cope with or expect because they are consequences of your own actions, do you really become aware of them. So he might not notice usually, but would if an error or something else unexpected occurred.
This is why 100ms, or even sometimes 200ms, is fine for many things, but others cause irritation despite delays of 40ms or sometimes significantly lower. The brain smooths out what it can, the rest sets of warnings of potential trouble.
I remember Dan posting that he typed at ~120wpm somewhere. 120wpm is 0.002 words per ms or 0.4 words per 200ms. Wouldn't one notice if they're almost halfway through a word and nothing has shown up on the screen?