How to organise the timing for event triggers, stimulus presentation and keypresses?

Coding
1

Hi! I am trying to code an experiment in psychopy which uses pyserial to send various triggers at the beginning/end of trials. My question is a general one regarding the organisation of code around stimulus timing and when to send triggers & record keypresses. I am using clock-based timing.

I want to send a trigger upon window flipping of my stimulus and have the simulus drawn using clock-based timing. How do I send a trigger at the same time as flipping & at the end of the trial but not upon every loop of my while statement, if that makes sense?

fixation_cross(1)
tapping_clock.reset()

port.write('K'.encode()) # Start trigger
    
while tapping_clock.getTime() < 10:
      tapping_text.draw()
      win.flip()
    
port.write('k'.encode()) # End trigger

I’m having the same issue with the code below where I want to send a start trigger upon presentation of the letter and have the ending trigger at the end of the trial (2 seconds) with keypresses being searched for inbetween.

nback_clock.reset()
nback_kb.clock.reset()
    while nback_clock.getTime() < 2:
        if nback_clock.getTime() < 0.5:
                letter_present.draw()
        else:
                blank.draw()
        win.flip()
        port.write('F'.encode()) # Start trial trigger
        port.write('f'.encode()) # End trial trigger

        keys_n = nback_kb.getKeys(keyList = ['left', 'right']) 
        
        # Get responses 
        if len(keys_n) > 0:
            if corrAns == keys_n[-1].name:
                answer = 1
            elif corrAns != keys_n[-1].name:
                answer = 0
                
        elif keys_n in ['', [], None]:
            answer = 'None'
        
        else:
            answer = 'error'

Sorry for all the questions, I have used psychopy before but I am not particularly well-versed in coding in psychopy and how to structure trials in this way. I would appreciate any help or advice as I can code it, I’m just unsure as how to structure it. Thank you! :slight_smile:

2

Try using the win.callOnFlip method:

fixation_cross(1)
tapping_clock.reset()

win.callOnFlip(port.write, 'K'.encode())   # Send start trigger on next win.flip()
 
while tapping_clock.getTime() < 10:
      tapping_text.draw()
      win.flip()
    
port.write('k'.encode()) # End trigger
1 Like
3

Oh great thank you! That looks like exactly what I need! :slight_smile:

Would you know whether to put the end trigger just after the key check part of the code (the end)?

4

If you only want to send the start trigger the first time letter_present is drawn, and the end trigger right after a key is pressed. or after the 2 second timeout period:

    start_marker_sent = False
    end_marker_sent = False
    while nback_clock.getTime() < 2:
        if nback_clock.getTime() < 0.5:
                letter_present.draw()
                if start_marker_sent is False:
                    win.callOnFlip(port.write, 'F'.encode())
                    start_marker_sent = True
        else:
                blank.draw()
        win.flip()

        keys_n = nback_kb.getKeys(keyList = ['left', 'right']) 
        
        # Get responses 
        if len(keys_n) > 0:
            if corrAns == keys_n[-1].name:
                answer = 1
            elif corrAns != keys_n[-1].name:
                answer = 0
            
            if end_marker_sent is False:
                port.write('f'.encode()) # End trial trigger
                end_marker_sent = True
    
        elif keys_n in ['', [], None]:
            answer = 'None'
        
        else:
            answer = 'error'

    # send end marker if no keys were pressed (timeout)
    if end_marker_sent is False:
        port.write('f'.encode()) # End trial trigger
1 Like
5

Thank you so much!! If I want the marker just at the end of the 2 second period, I just remove the end_marker_sent variable and just put the end trigger at the end of the while loop?

6

Yes, that as well as the first end trial trigger that was being sent if a key was pressed.

1 Like
7

Yes I’ll put the end trigger after/outside of the while loop