updating trial variable

Gar O'Connell

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Sep 3, 2015, 11:16:43 AM9/3/15

to jsPsych

Hi Josh,

Thanks for very useful tool. I am stuck on a basic issue - updating the value of a variable ("k" which indexes elements of stimulus array) between trials. Right now I just want to do something basic like switch it from 0 to 1 from the first to second trial, and I will add more complexity once I can do that. I thought the on_finish function would help, but it does not seem to pass back into the stimuli parameter. Below is my code:

Thanks for help,

Garret

var k = 1;

var optdelay = ["NOW", "1 MONTH"];

var optamount = ["50", "100"];

/* define test block */

var block = {

type: "single-stim",

stimuli: ["<div class='left center-content'><p style=color:white>" + optdelay[k] + optamount[k] + "</p>"],

choices: [37,39],

on_finish: function(){

var k = 0;

},

is_html: true

}

var timeline = [];

var while_loop_chunk = {

chunk_type: 'while',

timeline: [block],

continue_function: function(data) {

var response = JSON.parse(data[0].key_press); // convert JSON to array

if (response[0] == 37) {

return false; // continue the loop

} else {

return true;

}

Josh de Leeuw

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Sep 3, 2015, 11:22:10 AM9/3/15

to Gar O'Connell, jsPsych

Hi Garret.

The issue is that the block variable is evaluated before the experiment runs. So you are updating k correcty in on_finish(), but optdelay[k] is selected before the experiment runs.

You can get around this by using a function as the parameter value (http://docs.jspsych.org/features/functions-as-parameters/).

It would look like this:

var block = {

type: "single-stim",

stimuli: [function(){

return "<div class='left center-content'><p style=color:white>" + optdelay[k] + optamount[k] + "</p>";

}],

choices: [37,39],

on_finish: function(){

var k = 0;

},

is_html: true

}

By wrapping the parameter value in a function, jsPsych will wait until the trial begins to evaluate the function, and use whatever value the function returns as the parameter.

--Josh

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Gar O'Connell

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Sep 3, 2015, 12:50:23 PM9/3/15

to jsPsych

Hi Josh,

thanks for the advice. The code you edited runs fine, but again the variable does not update (i.e. the k=0 values of optdelay and optamount are not being displayed in trials). Also, the exit response (anything but arrow key 37) is not stopping the while chunk. Sorry for badgering. I just threw this code together from tutorials/forum so I am sure I have made a very basic error. Here is full code:

Thanks again.

<!doctype html>

<html>

<head>

</head>

</body>

/* define welcome message block */

var welcome_block = {

type: "text",

text: "<p style=color:white>Welcome to the experiment. Press any key to begin.</p>"

};

var k = 0;

var optdelay = ["NOW", "1 MONTH"];

var optamount = ["50", "100"];

/* define test block */

var block = {

type: "single-stim",

stimuli: [function(){

return "<div class='left center-content'><p style=color:white>" + optdelay[k] + optamount[k] + "</p>";

}],

choices: [37,39],

on_finish: function(){

var k = 1;

},

is_html: true

}

var timeline = [];

var thispress = 0;

var while_loop_chunk = {

chunk_type: 'while',

timeline: [block],

continue_function: function(data) {

var response = JSON.parse(data[0].key_press); // convert JSON to array

if (response[0] == 39) { // if the response is R

return false; // continue the loop

} else {

return true;

}

timeline.push(while_loop_chunk);

/* create experiment definition array */

//var experiment = [while_loop_chunk];

//experiment.push(welcome_block);

//experiment.push(instructions_block);

//experiment.push(trial);

/* start the experiment */

jsPsych.init({

experiment_structure: [welcome_block,while_loop_chunk],

on_finish: function() {

jsPsych.data.displayData();

}

});

</script>

</html>

Gar O'Connell

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Sep 4, 2015, 6:18:44 AM9/4/15

to jsPsych, gar...@hotmail.com

Hi Josh,

I figured out why it wasn't updating. Apparently already declared variables cannot be overwriting, so the individual elements need replacing e.g. instead of "var k = 1", "k[0] = 1". Thanks for help.