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A delay will always occur between a user action and an application response.

It is well known that the lower the response delay, the greater the feeling of the application responding instantaneously. It is also commonly known that a delay of up to 100ms is generally not perceivable. But what about a delay of 110ms?

What is the shortest application response delay that can be perceived?

I'm interested in any solid evidence, general thoughts and opinions.

I'm also running some simple online tests to examine these questions and would appreciate the participation of the SO community:
  > http://webignition.net/research/response-times/which-is-faster/

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I don't really get your question... Besides promoting your test site, what answers do you expect to get here?? –  Yuval Adam Feb 11 '09 at 10:55
@Yuval A: I am genuinely interested in opinions on the perception of application response delays. As for the research, it's of a purely academic nature, the results of which will be freely published in a few months' time. –  Jon Cram Feb 11 '09 at 19:13
"shortest perceivable" is different than shortest tolerable. I am pretty sure I could perceive a 200ms delay, But I think i could tolerate (and regard as 'instantaneous') a 1-3 second delay. Your question as phrased has to do with physiology and not UI –  Scott Evernden Feb 12 '09 at 0:01
0.0972365 seconds. Approximately. –  Hot Licks Nov 7 '11 at 17:04
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7 Answers

up vote 11 down vote accepted

What I remember learning was that any latency of more than 1/10th of a second (100ms) for the appearance of letters after typing them begins to negatively impact productivity (you instinctively slow down, less sure you have typed correctly, for example), but that below that level of latency productivity is essentially flat.

Given that description, it's possible that a latency of less than 100ms might be perceivable as not being instantaneous (for example, trained baseball umpires can probably resolve the order of two events even closer together than 100ms), but it is fast enough to be considered an immediate response for feedback, as far as effects on productivity. A latency of 100ms and greater is definitely perceivable, even if it's still reasonably fast.

That's for visual feedback that a specific input has been received. Then there'd be a standard of responsiveness in a requested operation. If you click on a form button, getting visual feedback of that click (eg. the button displays a "depressed" look) within 100ms is still ideal, but after that you expect something else to happen. If nothing happens within a second or two, as others have said, you really wonder if it took the click or ignored it, thus the standard of displaying some sort of "working..." indicator when an operation might take more than a second before showing a clear effect (eg. waiting for a new window to pop up).

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"any latency of more than 1/10th of a second ... begins to negatively impact productivity" - excellent, good to know. Did you learn this from a formal source such as a book? If so, can you recall where this comes from? –  Jon Cram Feb 12 '09 at 8:13
Unfortunately, no, I don't remember where that was from. I just remember being taught/told that back in grad school (or possibly before). My recollection was that it had come from a study (and I'm specifically remembering it having to do with typing, not necessarily a GUI). –  Rob Parker Feb 12 '09 at 16:24
BTW, grad school for me was back around 1992-1994. –  Rob Parker Feb 12 '09 at 16:25
An anonymous downvote with no explanation on an answer that had been accepted by the questioner (even if Matt Jacobsen's answer is more deserving for the specific references) on a nearly three-year-old question? That seems uncalled for (or maybe a mistake?). –  Rob Parker Dec 15 '11 at 19:27
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Persistence of vision is around 100ms so it should be a reasonable visual feedback delay. 110ms should make no difference, as it is an approximate value. In practice you won't notice a delay below 200ms.

Out of my memory, studies have shown that users lose patience and retry an operation after around 2s of inactivity (in the absence of feedback), e.g. clicking on a confirm or action button. So plan on using some kind of animation if the action takes longer than 1s.

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I worked on an application that had a explicit business goal of being blindingly fast, and we had a max allowed server time of 150ms for processing a full web page.

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What application was it that has a 'blindingly fast' as a business goal? –  Jon Cram Feb 11 '09 at 19:15
It was selling a specific type of product where most of the competition had really slow and clunky sites (for a reason). The business people thought there was business opportunity in making a really fast site. The site was an big success - although there's many reasons for that. –  krosenvold Feb 11 '09 at 19:31
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No solid evidence but for our own application, we allow a maximum of one second between a user action and feedback. If it does take longer, a "waiting box" should be shown.

A user should see "something" happening within a second of causing an action.

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I don't think anecdotes or opinions are really valid for answers here. This question touches on the psychology of user experience and the sub-conscious mind. The human brain is powerful and fast and mere milliseconds do count and are registered. I am no expert but I know there is much science behind e.g. what Matt Jacobsen mentioned. Check out Google's study here http://code.google.com/speed/files/delayexp.pdf for an idea of how much it can affect site traffic.

Here's another study by Akami - 2 second response time http://www.akamai.com/html/about/press/releases/2009/press_091409.html (From http://ux.stackexchange.com/questions/5529/once-apon-a-time-there-was-a-10-seconds-to-load-a-page-rule-what-is-it-nowa )

Does anyone have any other studies to share?

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For web applications 200ms is considered as unnoticable delay, while 500ms is acceptable.

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how did you come about these numbers? –  MorganTiley Nov 7 '11 at 16:43
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