// Generate positive set of length 'size' with a probe
// yes/no is not counter-balanced but fully randomized to about 50:50
// E.g., with size = 1, there is still a 50:50 chance of the probe being 1 or not
function getstimulus(size)
{
    var row = shuffle(range(1,10)),         // Array of digits 1 to 9 in random order
        pos = row.slice(0,size),            // First 'size' digits (also store in pos)
        neg = row.slice(size-9),            // Last digits not in positive_set (also store in neg)
        inpositive = Math.random() < 0.5;   // 50% chance of probe in positive set

    return { 
        set: pos,                           // Positive set
        inpositive: inpositive,             // true if probe is in positive set, else false
        probe: inpositive ? pos[randint(size-1)] : neg[randint(9-size-1)] // Keep yes/no ratio about 50:50
    }
}

// Returns a completely randomized design of lengths 1 to 6, where trials for each length are specified
function gettrials(trials_per_length)
{
    var trials = [], i, j;
    
    for (i = 0; i < trials_per_length; i++)
    {
        for (j = 1; j <= 6; j++)
        {
            trials.push(j);
        }
    }
    
    return shuffle(trials);
}

var middle = main.addblock('center',10,100,60)
    .style("border","thin solid lightgrey")
    .style("textAlign","left")
    .style("padding","1em")
    .text("<h2>Instruction</h2>You will see one to six digits appear for a short period."
        + "Try to remember these. Then they will disappear and a 'probe' digit will appear. "
        + "Type 'z' for Yes: the probe digit was in the list, "
        + "or '/' for No: it was not in the list. "
        + "Be as fast and accurate as you can.<br>"
        + "<i>Click the Start button or press the Enter key to start the experiment.</i>");
    
var left = main.addblock('left','bottom',25,10)
    .style("fontSize","0.8em")
    .style("color","gray")
    .text("<b>z</b> key = <b>Yes</b>");

var right = main.addblock('right','bottom',25,10)
    .style("fontSize","0.8em")
    .style("color","gray")
    .text("<b>/</b> key = <b>No</b>");

var ok = main.addblock('center',70,20,20).button('Start');
ok.await('click');

middle.clear()
    .style("border","0")
    .style("fontSize","2em")
    .style("textAlign","center");
ok.clear();

trials = gettrials(1);

var stimulus, positive_set, probe, inpositive, trialno, length, t1, e, score;

for (t = 0; t < trials.length; t++)
{
    stimulus = getstimulus(trials[t]);
    
    positive_set = stimulus.set.join(' ');  // turn array into a space-delimited string with join()
    probe = stimulus.probe; 
    inpositive = stimulus.inpositive; 
    trialno = t;
    length = trials[t];                     // trials[t] holds the number of items in positive set

    await(1000);
    middle.text(positive_set);        
    await(2000);
    middle.clear();
    await(250);
    middle.text(probe);
    
    t1 = now();
    e = await("keypress");
    rt = now() - t1;
//        storetrial("RT{stimulus}","{RT}","RT");

    middle.clear();

    score = 0;

    if (e.key.toLowerCase() === 'z' && inpositive)
    {
        score = 1;
    }

    if ((e.key === 'z' || e.key === '?') && !inpositive)
    {
        score = 1;
    }

    if (score)
    {
        middle.text("Correct!");
    }
    else
    {
        middle.text("Not correct");
    }


    if (e.key.toLowerCase() !== 'z' && e.key !== '/' && e.key !== '?')
    {
        middle.text("Please, press <b>z</b> or <b>/</b>");
        score = -1;
    }
        
    //log("RT: RT, Correct: score, length: length, trialno: trialno");

    await(1500);
    middle.clear();
}

await(1000);
middle.text("Finished!<br>Thank you for participating!");
await(2000);

You can download the files as follows: Click on the file (link) and then right-click and choose Save as... from the menu. Some media files (e.g., sound) will have a download button for this purpose.