Prevent key holding

[zameji]

By keeping track whether the key has been pressed and released, we prevent the user from keeping the key down and fast-forwarding through the sentence.
Inspired by a more general version on StackOverflow

[addrummond]

Hi Jiri, thanks for taking the time to submit this.

I don't think that there is any point in trying to stop users from doing this. If users want to go through the sentence as fast as possible without reading it, then they can do that, regardless of whether or not separate presses of the space bar are required. The best thing to do is to add comprehension questions, so that participants who answer a significant number of comprehension questions incorrectly can be filtered out.

This modification also adds a small degree of additional latency, since the next word is displayed only once the space bar is released.

See also discussion here:

https://groups.google.com/forum/#!searchin/ibexexperiments/hold$20key$20down$20space%7Csort:date/ibexexperiments/8_poa2W9zhA/gq1ITZogBAAJ

[zameji]

Hi & thanks for the quick response. I suppose we can't prevent the users completely, but I don't want to make it easy for them. This would also prevent the few cases where the user holds the spacebar too long and skips the next word by accident. Obviously, it's entirely up to you to decide whether it makes sense in the master branch or not.
Regarding the latency - actually, the next word is displayed immediately, it is only the word after that that is affected, waiting for the "keyup - keydown" event pair.

[addrummond]

Ah I see. Ok, I think I agree with the logic for including this. I may look into whether it's possible to do this without registering and unregistering event listeners.