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What is the shortest perceivable application response delay?
I've been profiling some JavaScript UI code because it feels a little laggy. So far, I've found some bottlenecks and optimized them out, but I'd like to define a measurable requirement for this.
How quickly should a response occur in order for a human not to notice lag? For example, what's the minimum detectable delay between when a keyboard key is pressed and when a letter appears on the screen? At what point is further optimization not going to make any difference to a human?
A lot of monitors have a refresh rate at about in the 60-120Hz range. Does that mean the magic number is around 8-16ms?