How to store values that keep changing after every trial in data of a trial?

[prashantig25]

Dear All,
I am trying to store data for each trial. In each trial, 2 gabor patches are displayed which have varying contrast levels. The contrast level changes after every trial through the on_start function. I want to store the contrast level for each trial in data. I am trying to do that by defining 'con' inside data and trying to store the value in it. But, when I run the experiment in Cognition.run, the column with 'con' is empty in the .csv file. Is there anyway I can fix it? Or is there any other way to store the contrast levels of each trial so that the data is stored for each trial? Here is part of the code:

var s0_r1_high60 = {
        type: 'canvas-keyboard-response',
        on_start: function(s0_r1_high60){
            s0_r1_high60.contrast = Math.random(); s0_r1_high60.contrast1 = jsPsych.currentTrial().contrast  + randbet(0.05,0.35);
        },
        stimulus: gabor,
        data: {
            condition: 'HH', state: '0', reward: '1', prob: '60_40', con: jsPsych.currentTrial().contrast, 
        },
        choices: keys, trial_duration: duration,response_ends_trial: false,
        on_finish: function (data) {
            if (data.key_press === rand60r1.pop()) {
                data.correct = true;
            } else {
                data.correct = false;
            }
        },
    };

Any help is appreciated. Thank you!

[JAQuent]

I am not sure if I understand the problem but do you have to change anything as function of previous trials or can you pretty much set everything up before? If the latter is the case, you can just create it in an array before:

var stimuli = new Array();
for (i = 0; i < nTrial; i++){
  stimuli[i] = {data: {condition: 'HH', 
                       state: '0', 
                       reward: '1', 
                       prob: '60_40', 
                       con: 'your contrast values here'}};
};

// Inside your s0_r1_high60 variable you set
data: jsPsych.timelineVariable('data'),


// Pushing it to the timeline
var experiment = {
  /// other arguments
  timeline_variables: stimuli,
  // other arguments
};
timeline.push(experiment);

[prashantig25]

Hi @JAQuent
Thank you but I can't pre-define. The contrast level is supposed to be different for every trial and it needs to change on every trial. I do that using the on_start function. But I want to store that value in the data for every trial. I hope that is clear.
Thanks.

[JAQuent]

Just to be clear. You can have the contrast level different every trial with that but what would not work with my suggestion is changing it as a function of previous trails (e.g. performance). Hope you'll find your solution.

…

On 17 February 2021 20:45:45 GMT, prashantig25 ***@***.***> wrote: Hi @JAQuent Thank you but I can't pre-define. The contrast level is supposed to be different for every trial and it needs to change on every trial. I do that using the on_start function. But I want to store that value in the data for every trial. I hope that is clear. Thanks. -- You are receiving this because you were mentioned. Reply to this email directly or view it on GitHub: #1520 (reply in thread)

-- Sent from my Android device with K-9 Mail. Please excuse my brevity.

[becky-gilbert]

Hi @prashantig25, sorry for the delayed response. I'm not sure if this is still helpful, but I thought I'd reply anyway.
I think the reason your method isn't working is because the jsPsych.currentTrial function that you have in the data parameter will run when the page first loads (before the experiment has started). So you could try making data a dynamic parameter, i.e. a function that returns the data object.

data: function() {
  return {condition: 'HH', state: '0', reward: '1', prob: '60_40', con: jsPsych.currentTrial().contrast};
}

If that doesn't work, another way to do this is to use a global variable to store the current contrast value during the experiment. You would change the value of this variable in the on_start function, and then access its value in the data parameter. Again, this means that your data parameter should be a function.

var curr_contrast = null;

var s0_r1_high60 = {
  type: 'canvas-keyboard-response',
  on_start: function(s0_r1_high60){
    s0_r1_high60.contrast = Math.random(); s0_r1_high60.contrast1 = jsPsych.currentTrial().contrast  + randbet(0.05,0.35);
    curr_contrast = s0_r1_high60.contrast;
  },
  stimulus: gabor,
  data: function() {
    return {condition: 'HH', state: '0', reward: '1', prob: '60_40', con: curr_contrast};
  },
  // etc.
};

Finally, are you using a modified version of the canvas-keyboard-response plugin that has a contrast parameter? If so, then you could just modify the plugin so that it saves the contrast parameter value to the trial data by default. Or if you're using jsPsych v.6.3.0, then you can use the save_trial_parameters parameter, which lets you save (or not save) any of the trial parameters:

var s0_r1_high60 = {
  type: 'canvas-keyboard-response',
  on_start: function(s0_r1_high60){
    s0_r1_high60.contrast = Math.random(); s0_r1_high60.contrast1 = jsPsych.currentTrial().contrast  + randbet(0.05,0.35);
    curr_contrast = s0_r1_high60.contrast;
  },
  stimulus: gabor,
  data: function() {
    return {condition: 'HH', state: '0', reward: '1', prob: '60_40'};
  },
  save_trial_parameters: {
    contrast: true  
  },
  // etc.
};