What is the threshold where actions are perceived as "instant"?
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.