Remembering Random Dot Patterns
Jaap MurreThe 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 ? "<b>old</b>. That is, you though you recognized it, but you this was a false memory." : "new."));
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