# Psychopy won't detect keypresses

**URL:** <https://discourse.psychopy.org/t/psychopy-wont-detect-keypresses/26016>\
**Category:** Coding\
**Created:** [November 16, 2021, 2:49pm UTC](https://discourse.psychopy.org/t/psychopy-wont-detect-keypresses/26016 "2021-11-16T14:49:46Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![sallicap](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sallicap](https://discourse.psychopy.org/u/sallicap)\
**Post date:** [November 16, 2021, 2:49pm UTC](https://discourse.psychopy.org/t/psychopy-wont-detect-keypresses/26016/1 "2021-11-16T14:49:46Z")

</div>

Hi I have a n-back task which detects spacebar keypresses using the following code.

```auto
# Setting up trial components
nback_clock = core.Clock()
nback_clock2 = core.Clock()

nback_kb1 = keyboard.Keyboard()
nback_kb2 = keyboard.Keyboard()
fix_cros = TextStim(win, text='+', height=0.15)

# Loading stimuli
nback_letters1 = pd.read_csv('nback_letters1.csv')['letters'].tolist()
nback_corrAns1 = pd.read_csv('nback_letters1.csv')['corrAns'].tolist()

nback_list1 = list(chunks(nback_letters1, 48)) 
nback_corrAns = list(chunks(nback_corrAns1, 48)) 

# Data saving
nback_results = pd.DataFrame(columns = ['Trial number', 
                                        'Stimulus presented', 
                                        'Key pressed', 
                                        'Correct answer', 
                                        'Response', 
                                        'Reaction time'])

# Begin trials for n-back 1 
for i in nback_list1:
    for j in range(0, len(i)):
        
        nback1_start = datetime.now()
        
        if kb.getKeys(keyList=['escape']):
            shutdown()
            
        corrAns = nback_corrAns1[j]
        thisLetter = nback_letters1[j]
        letter_present = TextStim(win, text=nback_letters1[j], height=0.5)
        
        fixation_cross(0.5)
        
        if j != 0:
                          
            # Use clock-based timing
            nback_clock.reset()
            
            start_marker_sent = False
            tStart =nback_clock.getTime()
            nback_kb1.clock.reset()
            
            while nback_clock.getTime() < 2.5:
                if nback_clock.getTime() < 0.5:
                    letter_present.draw()
                    if start_marker_sent == False:
                        win.callOnFlip(port.write, 'F'.encode())
                        start_marker_sent = True
                else:
                    blank_.draw()
        
                win.flip()
                      
                keys_n = nback_kb1.getKeys(keyList = ['space']) 
                
                tResp = nback_clock.getTime()
                response = 'None' if not keys_n else keys_n[-1]
            
            port.write('f'.encode())
                            
            # Get responses 
            if keys_n:
                RT = (tResp - tStart)-0.5
                if corrAns == response or str(corrAns) == response:
                    answer = 1
                elif corrAns != response:
                    answer = 0
                    
            elif response == 'None':
                RT = 0
                if corrAns == '' or corrAns == [] or corrAns == None or corrAns == 'None':
                    answer = 1
                else:
                    answer = 0
            
            else:
                answer = 'error'
            
            # Saving trial data
            thisExp.addData('N back RT',RT)
            thisExp.addData('Stimulus presented',thisLetter)
            thisExp.addData('N back response',answer)
            thisExp.addData('N back start',nback1_start)
            thisExp.addData('Key pressed', response)
            thisExp.addData('Trial number', j)
            thisExp.nextEntry()
            
            # Saving response data
            nback_results = nback_results.append({'Trial number': j, 
                                                    'Stimulus presented': thisLetter,
                                                    'Key pressed': response,
                                                    'Response': answer,
                                                    'Reaction time': RT}, ignore_index=True)
                        
        else:
            nback_clock.reset()
            while nback_clock.getTime() < 2.5:
                if nback_clock.getTime() < 0.5:
                    letter_present.draw()
                else:
                    blank_.draw()
                win.flip()

```

When I then look at the csvs it says response = None and that a key wasn’t pressed. Why is this happening? I would appreciate any help 🙂 Thank you!

---

<div class="post-metadata">

**Author:** ![sol](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/sol/32/15018_2.png) [@sol](https://discourse.psychopy.org/u/sol)\
**Post date:** [November 17, 2021, 12:31pm UTC](https://discourse.psychopy.org/t/psychopy-wont-detect-keypresses/26016/2 "2021-11-17T12:31:42Z")

</div>

I think the issue is that the call to:

```auto
keys_n = nback_kb1.getKeys(keyList = ['space'])

```

is within a 2.5 second loop, so it will be called repeatedly during this time period, even if a key event has already been detected, overwriting the earlier detected key. To fix this, only get `keys_n` until one is detected during the 2.5s seconds, then stop checking for keys and recalculating `response`.

The other thing is that:

```auto
keys_n = nback_kb1.getKeys(keyList = ['space'])

```

will return the key after a release is detected, not when the key is just pressed. If this is intended, leave the code as is, otherwise use `waitRelease=False`:

```python
# return a key when it is pressed, not when it is released
keys_n = nback_kb1.getKeys(keyList = ['space'], waitRelease=False)

```

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<div class="post-metadata">

**Author:** ![sallicap](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sallicap](https://discourse.psychopy.org/u/sallicap)\
**Post date:** [November 17, 2021, 3:13pm UTC](https://discourse.psychopy.org/t/psychopy-wont-detect-keypresses/26016/3 "2021-11-17T15:13:39Z")

</div>

Perfect, thank you! How does one get it to stop checking keys after a response?

Would one use a boolean `key_pressed = False` before the while loop begins & then a `key_pressed = True` after the getKeys function? Although this would still overwite itself every loop…