[open] Log response time of button press via serial port

Comments

• sebastiaan

  July 2014 edited 5:46PM

  Hi Stefania and Ambra,

  Assuming that your button box simply sends a response as soon as a press has been detected, you can just use OpenSesame's self.time() function to get the time immediately after you have collected the response, like so:

  # Your response collection code here
  response_timestamp = self.time()
  exp.set('response_timestamp', response_timestamp)
  

  This will log the timestamp of the response, not the response time relative to some other event, such as the presentation of a sketchpad. But you can deduce the response time easily, simply subtracting the timestamp of the starting event from the timestamp of the response.

  Cheers!
  Sebastiaan

  
  
  Check out SigmundAI.eu for our OpenSesame AI assistant!
  
• ambraferrari

  July 2014 edited 5:46PM

  Hi Sebastiaan,
  thank you for your immediate response, that we really appreciated.

  However, if the subject presses the button while the stimulus is still being presented (60 frames), the serial port receives a response during the loop. We only read the response after that loop, so this means that self.time() does not necessarily report the precise time of button press (i.e. when it occurred during the loop).

  We probably need a parallel pooling loop that reads the serial port (and uses self.time() to get the actual time of presses) inside the presentation loop. Is that correct? again, any suggestions will be very welcome.

  Thanks, Stefania and Ambra
• Edwin

  July 2014 edited 5:46PM

  Hi guys,

  Actually, you could do this in a serial fashion, rather than using the more complicated parallel threading approach. Place the following code in an inline_script placed directly behind the sketchpad that you use to present your stimulus, and set the duration of that sketchpad to 0.

  # get the starting time
  t0 = self.time()
  
  # determine the presentation time in milliseconds
  # (= Nframes * (1/refresh rate in Hz) * 1000 - half a frame time)
  Nframes = 60 # frames
  refrate = 60 # Hz
  frametime = (1.0 / refrate) * 1000
  prestime = int(Nframes * frametime - (frametime/2))
  
  # run until the presentation time passes or a response is made
  response = None
  while self.time() - t0 < prestime and response == None:
      # get the button response
      response = # PLACE YOUR CODE HERE
      # check if there is a response
      if response != None:
          # set the OpenSesame response variables
          exp.set('response_timestamp', t0)
          exp.set('response', response)
          # save a timestamp
          t1 = self.time()
  
  # pause for the remainder of the stimulus duration
  if response != None:
      self.sleep(prestime - (t1-t0))
  

  Does that work for you?
• Xandra

  October 2014 edited 5:46PM

  First of all thanks for putting out this great program! Quick question: in PsychoPy it is possible to start recording keypresses at certain frames. My experiment uses a paradigm where I need a 'beep' played at a certain frame (the first after an edit) and the participant will then press a button, the RT time of which also needs to be recorded. How do I anchor the keypress, the recording, and the sound to a certain frame?
• sebastiaan

  October 2014 edited 5:46PM

  Hi Xandra,

  My experiment uses a paradigm where I need a 'beep' played at a certain frame (the first after an edit) and the participant will then press a button, the RT time of which also needs to be recorded. How do I anchor the keypress, the recording, and the sound to a certain frame?

  That really depends on how your experiment is structured. What does your trial look like exactly and how have you implemented it at the moment?

  Cheers,
  Sebastiaan

  
  
  Check out SigmundAI.eu for our OpenSesame AI assistant!