There are some missing details in the specification given in the question, so I am going to make the following assumptions:
- Item one only one key-press is expected - let's say a press on the left or right arrow key
- Item two immediately after the response is given the waiting for response stops - the time taken to make the response is the reaction time
The follwing code should implement your requirements according to the above assumptions
% improve portability of your code acorss operating systems
KbName('UnifyKeyNames');
% specify key names of interest in the study
activeKeys = [KbName('LeftArrow') KbName('RightArrow')];
% set value for maximum time to wait for response (in seconds)
t2wait = 2;
% if the wait for presses is in a loop,
% then the following two commands should come before the loop starts
% restrict the keys for keyboard input to the keys we want
RestrictKeysForKbCheck(activeKeys);
% suppress echo to the command line for keypresses
ListenChar(2);
% get the time stamp at the start of waiting for key input
% so we can evaluate timeout and reaction time
% tStart can also be the timestamp for the onset of the stimuli,
% for example the VBLTimestamp returned by the 'Flip'
tStart = GetSecs;
% repeat until a valid key is pressed or we time out
timedout = false;
% initialise fields for rsp variable
% that would contain details about the response if given
rsp.RT = NaN; rsp.keyCode = []; rsp.keyName = [];
while ~timedout,
% check if a key is pressed
% only keys specified in activeKeys are considered valid
[ keyIsDown, keyTime, keyCode ] = KbCheck;
if(keyIsDown), break; end
if( (keyTime - tStart) > t2wait), timedout = true; end
end
% store code for key pressed and reaction time
if(~timedout)
rsp.RT = keyTime - tStart;
rsp.keyCode = keyCode;
rsp.keyName = KbName(rsp.keyCode);
end
% if the wait for presses is in a loop,
% then the following two commands should come after the loop finishes
% reset the keyboard input checking for all keys
RestrictKeysForKbCheck;
% re-enable echo to the command line for key presses
% if code crashes before reaching this point
% CTRL-C will reenable keyboard input
ListenChar(1)
