Prevent keyboard key from being held down

I am a complete MATLAB novice and am using it with psychtoolbox to create a word reaction time task with a timed memory element.

At the moment if the 't' key is pressed the elapsed time is displayed for 2.5 seconds, however if a the 't' key is held down it prevents the next word from being displayed, because of this...

while KbCheck WaitSecs(0.1); end

If I delete this then the words are displayed correctly but if the 't' key is held down the elapsed time is displayed constantly, which means participants could cheat the timed memory aspect.

Is there an easy way to prevent this, for example an auto key release, I want the elapsed time to be displayed for 2.5 seconds regardless of whether the 't' key is help or pressed.

Thanks if advanced, hope that is clear enough.