[solved] How to pseudorandomise blocks in a Go/Nogo task?

Comments

• Josh

  March 2016 edited 5:50AM

  Hi Tom,

  Are you sure you want to do that? Participants will surely learn that after every "go", the next trial is going to be a no-go. This will mess up your data. Moreover, following your rule, there could still be a sequence of 4 successive no-go trials...

  Cheers,

  Josh
• tomchatwin

  March 2016 edited 5:50AM

  Hi Josh, thanks for your reply. Sorry, I explained incorrectly.

  I want to make sure a pattern is kept whereby a neutral Go condition is always followed by an emotional Go condition.

  My conditions are:

  Happygo (emotional go)
  Happynogo (neutral go)
  Angrygo (emotional go)
  Angrynogo (neutral go)
  Sadgo (emotional go)
  Sadnogo (neutral go)
  Feargo (emotional go)
  Fearnogo (neutral go)

  In the 3 emotional Go conditions, an emotional expression is the Go stimulus and a neutral expression is the Nogo stimulus. In the 3 neutral Go conditions, the neutral expression is the Go stimulus and an emotional expression is the Nogo stimulus.

  I would like to find a way of randomising the order of the blocks but make sure neutral go and emotional go conditions are alternated. In each condition there are 30 trials.
• Josh

  March 2016 edited 5:50AM

  Hi Tom,

  Just to be sure... when you say "neutral go and emotional go conditions are alternated", do you mean alternating from trial to trial, or from block to block?

  Do you want the types of emotions to be randomized from trial to trial, or from block to block so that within one block it's always the same emotion?

  Cheers
• tomchatwin

  March 2016 edited March 2016

  Hi Josh

  Thanks for your reply.

  I have already managed to randomise trial items within each block. The trial sequence consists of 30 images - 21 Go and 9 Nogo stimuli- which are randomised using the "random" function in the loop menu.

  However, the problem I have is with the sequence of blocks within the experimental loop. In total, there are 8 blocks. In block 1, happy faces are the go cue and neutral faces are the nogo cue. In block 2, neutral faces are the Go cue and happy faces are the Nogo cue, etc, etc. Thus, each of the four emotions is paired with the neutral expression in both Go and Nogo conditions.

  The experiment measures performance when four emotions are Go cues and also when the same four emotions are Nogo cues. It will allow me measure emotion discrimination and at the same time emotion regulation (i.e. how the emotional context disrupts cognitive control).

  I could just randomise the experimental loop, the same way I did the trial sequence - e.g. by using the "random" function the loop menu. However, if I do this then (sometimes) all four conditions when the emotional cue is the Nogo stimulus are presented sequentially which means neutral faces are the target in 4 sequential blocks.

  I am worried that this could cause participant fatigue and produce an habituation effect.

  I would like to find a way to make sure that the 4 blocks in which the emotional faces are Go stimuli are alternated with the 4 blocks in which neutral faces are Go stimuli. This would make sure that the participant is always presented with a different target as they progress through the blocks.

  In sum, each block consists of 30 trials which I have randomised successfully.
  There are 8 blocks: 4 blocks have neutral as the go stimuli and 4 have an emotional expression as the go stimuli.
• Josh

  March 2016 edited 5:50AM

  Hi Tom,

  Thanks for the clarification. As your 8 blocks are contained by 8 loop items (I assume), you could in each respective loop item define the variable go with value set to emotional for blocks 1,3,5 & 7 and neutral for blocks 2,4,6 & 8. Since it's only 8 blocks, you can just do this manually.

  If you want to randomize whether block 1 go-stimuli are emotional or neutral (with go-stimuli for subsequent blocks defined accordingly), you can start your experiment with an inline script with code like

     import random
     exp.go_stimuli = ['emotional','neutral']
     random.shuffle(exp.go_stimuli)
  

  The go variables in your 8 block loops can then be set to [go_stimuli[0]] and [go_stimuli[1]] in alternating fashion.

  So in sum, it just comes down to defining your variables in each loop item, and picking stimuli based on those variables.

  Does that help?

  Cheers

  Josh
• tomchatwin

  March 2016 edited 5:50AM

  Thank you so much, Josh.

  I entered the inline script and it appears to be exactly what is needed to randomise a pattern of Go - Nogo through the blocks.

  I really can't thank you enough.

  Best wishes

  Tom
• tomchatwin

  March 2016 edited March 2016

  Hi Josh

  It seems it didn't work as when I test the experiment the neutral-go block sometimes occur contiguously.

  I added the code at the start of the experiment.

  I defined a variable "go" in the block loop with values "emotion" and "neutral". See link below:

  http://img.cogsci.nl/uploads/56e73a59d45b4.jpg

  I also defined a variable "go" within the respective trial loops with values [go_stimuli[0]] and [go_stimuli[1]]. See link below:

  http://img.cogsci.nl/uploads/56e739bccdd11.jpg
• Josh

  March 2016 edited 5:50AM

  Hi Tom,

  If you define the variable "go" twice, then the second one will overwrite the first, so they'll have to be named differently. Your first block loop seems problematic as well though... You defined a variable condition and a variable go, but looking at their values they are logically the exact same thing right?

  I would think your experimental design is a 2 x 4 x 2 factorial: emotional stimulus (yes/no), emotion type (happy/sad/fear/angry), and go (emotion, neutral). The order of appearance for the first one is randomized, within each of the eight blocks. Both the second and the third factor seem to be pre-set in your experiment, since you have a happy-go block, followed by a happy-nogo block, etc. If that's what you want (why not randomize emotion types within blocks?), then you don't have to perform funky tricks whatsoever. E.g. in the happy-go block, you could make do with 2 variables: stimulus_type (with values 'happy' and 'neutral'), and response (with values 'go' and 'nogo'). So that's 2 variables, 2 cycles, and you set it to repeat 15 times.

  Cheers

  Josh