{"id":216,"date":"2020-12-13T13:42:13","date_gmt":"2020-12-13T17:42:13","guid":{"rendered":"http:\/\/blog.labhackers.com\/?p=216"},"modified":"2020-12-21T12:26:47","modified_gmt":"2020-12-21T16:26:47","slug":"test-visual-stimulus-onset-timing-using-keyboard-events","status":"publish","type":"post","link":"https:\/\/blog.labhackers.com\/?p=216","title":{"rendered":"Test Visual Stimulus Onset Timing using Keyboard Events !?"},"content":{"rendered":"\n

Originally posted on March 6, 2019.<\/sup><\/p>\n\n\n\n

In this post we look at how to use the MilliKey <\/a>DeLux light sensor upgrade to test visual stimulus onset timing using PsychoPy<\/a> Coder by checking for a keyboard event.<\/p>\n\n\n\n

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The MilliKey DeLux is an affordable and easy to use light sensor attachment for MilliKey response boxes. The MilliKey DeLux can generate light level driven 1000 Hz USB serial or keyboard events<\/strong> that are read by the same experiment software controlling visual stimulus presentation.<\/p>\n<\/div><\/div>\n\n\n\n

In a previous post about Testing PsychoPy event.waitKeys() Event Timing<\/a>, we demonstrated how to use the MilliKey to test the keyboard event time stamping accuracy of the experiment software. This was achieved by sending USB serial messages from the experiment software instructing the MilliKey to generate keyboard events and then comparing the key press time to the time the serial message was sent. We found that, at least on Windows and Linux, PsychoPy can accurately time stamp MilliKey 1000 Hz keyboard events with one millisecond average delay and sub-millisecond variability.<\/p>\n\n\n\n

One of the unique features of the MilliKey DeLux is that it can be configured to generate a letter \u2018l\u2019 key press event when the light sensor brightness crosses a trigger threshold level. This allows you to assess visual stimulus onset timing of an experiment by using the standard keyboard event handling functionality of the software being used.<\/p>\n\n\n\n

PsychoPy Coder Test Script<\/h2>\n\n\n\n

Lets start by creating a simple PsychoPy Coder demo that repeatedly:<\/p>\n\n\n\n

  • clears the screen to black<\/li>
  • draws a white screen<\/li>
  • waits for a keyboard press event<\/li>
  • prints time difference between reported keyboard event and stimulus onset (white screen) times.<\/li><\/ul>\n\n\n\n
    #!\/usr\/bin\/env python\n# -*- coding: utf-8 -*-\nfrom __future__ import absolute_import, division, print_function\nfrom psychopy import visual, event, core\n\n# Number of dark -> light display change tests to run\ntest_count = 10\n\n# Create a full screen window and two full screen stim.\nwin = visual.Window(fullscr=True, screen=0)\nwhite_stim = visual.ShapeStim(win, lineColor='white', fillColor='white',\n                              vertices=((-1,-1),(1,-1),(1,1),(-1,1)))\ndark_stim = visual.ShapeStim(win, lineColor='black', fillColor='black',\n                             vertices=((-1,-1),(1,-1),(1,1),(-1,1)))\n\n# draw \/ setup both stim\nwhite_stim.draw()\ndark_stim.draw()\nwin.flip()\n\n# Manually press any key to start test\nevent.waitKeys(timeStamped=True)\n\nprint(\"trial\\tRT\\tkey_time\\tflip_time\\tkey\")\n# run test_count loops\ncount=0\nwhile count < test_count:\n    # Draw black screen and display it for about 0.5 seconds.\n    dark_stim.draw()\n    win.flip()\n    core.wait(0.5)\n # Throw away any possible junk keys\n # prior to changing display \n    event.getKeys()\n \n    # Draw white (target) stim and flip to it,\n    # getting time flip occurred (stim onset)\n    # time from psychopy.\n    white_stim.draw()\n    ftime = win.flip()\n\n # Key keyboard event and print time difference between\n # flip() time and keypress time.\n    k, ktime = event.waitKeys(timeStamped=True)[0]\n    kdelay = ktime - ftime    \n    print(\"%d\\t%.6f\\t%.6f\\t%.6f\\t%s\"%(count, kdelay, ftime, ktime, k))\n\n    core.wait(0.25)\n    count+=1<\/code><\/pre>\n\n\n\n
    We have basically created the most simple of manual reaction time tests. Run the above script from PsychoPy Coder and press a key as quickly as you can each time the screen turns white.<\/p>\n\n\n\n
    For example, running the example and manually pressing the space key, I get output like:<\/p>\n\n\n\n
    trial\tRT\tkey_time\tflip_time\tkey\n0\t0.368140\t1.687949\t2.056089\tspace\n1\t0.171302\t2.570518\t2.741820\tspace\n2\t0.197275\t3.256913\t3.454187\tspace\n3\t0.198487\t3.967356\t4.165843\tspace\n4\t0.196070\t4.679771\t4.875841\tspace\n5\t0.215323\t5.390571\t5.605894\tspace\n6\t0.197549\t6.118132\t6.315682\tspace\n7\t0.193179\t6.828715\t7.021894\tspace\n8\t0.166193\t7.535785\t7.701978\tspace\n9\t0.193039\t8.214774\t8.407813\tspace<\/pre>\n\n\n\n
    So far this has all been kind of boring right?<\/p>\n\n\n\n
    What if we could use this exact script<\/em> to test the visual onset timing of the white screen? Lets do it using the MilliKey DeLux.<\/p>\n\n\n\n
    MilliKey DeLux Setup<\/h2>\n\n\n\n
    For this test to work we first need to make sure the MilliKey DeLux is configured to:<\/p>\n\n\n\n
    1. use a sensible threshold level for the monitor being Generate Keyboard Events.<\/li>
    2. auto generate light sensor triggered keyboard events.<\/li><\/ol>\n\n\n\n
      Lets do this using the LabHackers\u2019 Device Manager application.<\/p>\n\n\n\n
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      MilliKey DeLux light sensor settings are found on the DeLux tab of the LabHackers\u2019 Device Manager application.<\/p>\n\n\n\n
      For this example use the following settings:
      Trigger Type<\/strong>: \u2018Keyboard Event\u2019
      Trigger Delay<\/strong>: 5 msec
      Enable Background Processing<\/strong>: Checked \/ True<\/p>\n<\/div><\/div>\n\n\n\n
      The Trigger Threshold<\/strong> setting can be set using the auto threshold feature of the Light Sensor Dialog. The following video is a screen capture from a Windows 10 computer running the Labhackers\u2019 Device Manager application. It illustrates using the auto threshold feature to set the light sensor threshold to an appropriate level for the monitor being tested. The MilliKey DeLux hardware, which can not be seen in the video, was placed over the white rectangle of the test dialog on the LCD monitor.<\/p>\n\n\n\n
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