What is the threshold where actions are perceived as "instant"? In Human Computer Interaction and User Experience there's some oft repeated rules of performance:


0.1 second is about the limit for having the user feel that the system is reacting instantaneously, meaning that no special feedback is necessary except to display the result.
1.0 second is about the limit for the user's flow of thought to stay uninterrupted, even though the user will notice the delay....
10 seconds is about the limit for keeping the user's attention focused on the dialogue...


I'm most interested in this &quot;instantaneous&quot; response. Related is this User Experience Question. A related answer does bring up some sources:

Card, S. K., Robertson, G. G., and Mackinlay, J. D. (1991). The information visualizer: An information workspace. Proc. ACM CHI'91 Conf. (New Orleans, LA, 28 April-2 May), 181-188.
Miller, R. B. (1968). Response time in man-computer conversational transactions. Proc. AFIPS Fall Joint Computer Conference Vol. 33, 267-277.
Myers, B. A. (1985). The importance of percent-done progress indicators for computer-human interfaces. Proc. ACM CHI'85 Conf. (San Francisco, CA, 14-18 April), 11-17.

However I can't access any copies of those articles. Also, frankly, they're all conference papers. Big HCI research often debuts at conferences, but ideally I'd like something robust which has been tested rather than something written 20-40 years ago for a conference.
One thing I've noticed is the &quot;instant response&quot; threshold quoted tends to be around 100ms to 200ms. Typical human reaction time is about 200ms so I'm wondering if there is a relation there. It seems possible; if something happens so quickly you can't react to it, it is practically &quot;instant&quot; in a way.
Approximately what length of time between action and reaction is perceived as instant by humans?
Preface

This is a very interesting question, that is also somewhat related to my area of research. I know of several related results (which I might add later in an edit), and I thought that with a few minutes of scholar search I'll find a paper dealing with this question exactly. I was surprised to find no such papers. So I decided to conduct an experiment...

Answer (preliminary. hopefully, will be edited)

As with many cases in psychology, the threshold is completely non-existant: there is no delay up to which the reaction is perceived as instantaneous, and after which it is perceived as delayed. You can measure the probability of the subject perceiving a delay, as a function of the delay time. You can choose any probability you want, arbitrarily, and call it the 'threshold'. If we decide on 50% (the chance of responding there was a delay is identical to the chance of responding it was instantaneous) then for me it is about 110ms.



The results presented here are based on 100 trials, performed by myself. Hardly counts as good study, but if a few more people run the test, I promise to process the results and post them here (and who knows, maybe even publish it somewhere :))

To participate in the experiment yourself


Sign up to ofri.webfactional.com. (It is a site I developed for web-based experiments conducted in my lab. It's still in beta, which is why its under a domain with my name, and not under huji.ac.il.  I promise we do not use your email for anything except for identifying you. No spam ever).
In the Group Name field in the registration, enter instant.
Login, and follow the on-screen instructions. Its really simple.
After running more than 60 trials another button will appear with the text 'show results'. Clicking it will draw a graph similar to the one presented here, based on your personal results.