demonstration of time-stamped keyboard polling with psychopy

responseTimeTimestamped.py

from psychopy import visual, event, core
import numpy as np
"""Record response latency
"""
respClock = core.Clock()

Hz = 60
#create a window to draw in
bgColor=np.array([-1,-1,-1])
scrn = 0; fullscrn= 0
myWin =visual.Window(color=bgColor, allowGUI=False,screen=scrn,fullscr=fullscrn, units='pix',waitBlanking=False)
respText = visual.TextStim(myWin,pos=(0, 0),color=(1,1,1),colorSpace='rgb',alignHoriz='center', alignVert='center', units='norm',autoLog=False)
respText.setText('Press up arrow or down arrow')
core.wait(.2)
for i in xrange(50): #go through 50 frames that show nothing. 
    #Because sometimes the operating system / graphics pipeline needs to clean up its act before accurate timing ensues
    myWin.flip()
    
maxRespTime = 3 #sec
frame = 0

respText.draw()
myWin.flip()
respClock.reset()
#using time stamps. Therefore not polling keyboard explicitly, event will do it automatically, instead in loop until maxRespTime reached
while frame < maxRespTime*Hz:

    frame += 1
    respText.draw()
    myWin.flip()


#check the key buffer
resp = 0
keysAndTimesPressed = event.getKeys(timeStamped=respClock) #time stamping causes it to return a tuple
print 'num keys pressed = ',len(keysAndTimesPressed)

for key in keysAndTimesPressed:
     respMade = True
     print 'key=',key
     if key[0] in ['up','down']: #up arrow or down arrow
        respLatencySecs = key[1]
        respMade = True
        if key[0]=='up':
            resp = 1
        if key[0]=='down':
            resp = -1
     print 'Response latency according to respClock = ', np.around(respLatencySecs,3), 'seconds'