Remembering Random Dot Patterns Demo Experiment Run Experiment

Remembering Random Dot Patterns

Jaap Murre

The following experiment is a very much abbreviated version of a dot pattern learning experiment pioneered by Posner and Keele in 1968. Try to remember a number of random dot patterns and then see whether you can recognize them reliably. This is harder than you think!

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var pattern = new Box(),
    coords = [[20,20],[30,40],[30,80],[40,30],[45,60], 
              [60,10],[60,75],[70,50],[80,20],[75,45]],
    no_of_targets = 5, study_time = 2000, series,
    hits = 0, false_alarms = 0, prototype_alarm = 0;

function showPattern(coords)
{
    var block, blocks = [], i;
    
    for (i = 0; i < coords.length; i++) 
    {
        block = pattern.addblock(coords[i][0],coords[i][1],10,10);
        block.text("•",200);
        blocks.push(block);
    }
    
    return blocks;
}

function distortCoordinates(coordinates,distortion,seed)
{
    var i,
        c = coordinates;
    
    distortion = distortion || 10;
    
    Math.seedrandom(seed);      // Make distortion repeatable with `seed`
    for (i = 0; i < c.length; i++) // Distort all coordinates
    {
        c[i][0] += randint(-distortion,distortion);
        c[i][1] += randint(-distortion,distortion);
    }
    
    return c;
}

function presentStimuli(indices,distortion)
{
    var c, i, p;
    
    for (i = 0; i < indices.length; i++)
    {
        p = indices[i];
        c = distortCoordinates(coords,distortion,p); // Use p as seed
        showPattern(c);
        await(study_time);
        pattern.clearall();                // Remove pattern from screen
        await(1000);
    }
}

function getResponses(indices,distortion)
{
    var c, i, p, e;
    
    for (i = 0; i < indices.length; i++)
    {
        p = indices[i];
        if (p === -1)
        {
            c = coords; // -1 means: show the prototype
        }
        else
        {
            c = distortCoordinates(coords,distortion,p); // Use p as seed
        }
        showPattern(c);
        e = awaitkey("s,l");
        
        if (e.key ===  "s") // Pattern believed to be old
        {
            if (-1 < p && p < no_of_targets)
            {
                ++hits; // Targets have indices 0,1,2, ..., no_of_targets-1
            }
            else
            {
                ++false_alarms;
            }
            
            if (p === -1)           // Prototype has index -1
            {
                ++prototype_alarm; // False recognition of prototype
            }
        }
        pattern.clearall();                // Remove pattern from screen
        await(1000);
    }
}

instruction("Study the following random dot patterns for later recognition. " 
          + "Patterns appear automatically.");
presentStimuli(range(no_of_targets),5);
instruction("Try to recognize the following patterns. "
          + "Type the 's' or 'S' for an old or 'seen' pattern and 'l' or 'L' for a new pattern");
series = shuffle(range(-1,2*no_of_targets));
getResponses(series);
text("You had " + hits + " hits and you recognized the prototype as " 
   + (prototype_alarm ? "old. That is, you though you recognized it, but you this was a false memory." : "new."));
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