Digit Span Task Demo Experiment Run Experiment

Digit Span Task

Jaap Murre

This is a fairly typical implementation of the digit span forward task, similar to what one might encounter in a neuropsychological test battery. The task takes less than 5 min and can be done on a PC with a mouse or on a large touchscreen (tablet or large mobile phone). The digit span is reported at the end of the task.

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var stimuli_forward = [
    [[],                 [] ],    
    [[1],                [1] ],
    [[9,7],              [6,3] ],
    [[5,8,2],            [6,9,4] ],    
    [[7,2,8,6],          [6,4,3,9] ],     
    [[4,2,7,3,1],        [7,5,8,3,6] ],    
    [[3,9,2,4,8,7],      [6,1,9,4,7,3] ],    
    [[4,1,7,9,3,8,6],    [6,9,1,7,4,2,8] ],    
    [[3,8,2,9,6,1,7,4],  [5,8,1,3,2,6,4,7] ],    
    [[2,7,5,8,6,3,1,9,4],[7,1,3,9,4,2,5,6,8] ]    
];

var stimuli_forward_example = [
    [[],                 [] ],    
    [[1],                [1] ],
    [[1,2],              [4,2] ],
    [[7,8,2],            [5,1,3] ]
];  

main.setfontsize(60);

instruction("First, you will do a brief example of the task");
digit_span_forward_example();
instruction("Now comes the real task");
digit_span_forward();


function digit_span_forward_example()
{
    var digits, span, trial, i, answer, correct, mistakes, total_correct = 0, 
        finished = false;

    instruction('You will see a number of digits in succession.'
    + ' They are only shown once.'
    + ' After the digits have been shown, you must repeat them in the same order by'
    + ' clicking on the numbers at the bottom of the screen.'
    + ' There are several series of numbers.'
    + ' The series are getting longer and longer.', 'OK', 'Instruction');
    
    instruction('We will start with a brief example so you can practice for a while', 'OK', ' ');

    for (span = 3; span < 4; span++)
    {
        mistakes = 0;
        for (trial = 0; trial < 2; trial++) // Subjects get two chances
        {
            digits = stimuli_forward_example[span][trial];
    
            await(2000);
            for (i = 0; i < digits.length; i++)
            {
                text(digits[i],300);
                await(1000);
                clear();
                await(500);
            }
        
            answer = get_answer(10000);
        
            correct = matches(digits,answer); 
            
            if (correct < answer.length)
            {
                await(500);
                alert("Make sure you click on the digits in the same order as presented");
            }
            else
            {
                ++total_correct;
            }
        }
    }
    
//    log(total_correct,"total_correct_digit_span_forward_example");
}
    
function digit_span_forward()
{
    var digits, span, trial, i, answer, correct, mistakes, total_correct = 0, 
        finished = false;

    var t0 = now();

    for (span = 2; span < 10; span++)
    {
        mistakes = 0;
        for (trial = 0; trial < 2; trial++) // Subjects get two chances
        {
            digits = stimuli_forward[span][trial];
    
            await(2000);
            for (i = 0; i < digits.length; i++)
            {
                text(digits[i],300);
                await(1000);
                clear();
                await(500);
            }
        
            answer = get_answer();
        
            correct = matches(digits,answer); 
    
            if (correct !== span)
            {
                ++mistakes;
            }
            else
            {
                ++total_correct;
            }
            
            if (mistakes === 2)
            {
                finished = true;
            }
        }
        
        if (finished)
        {
            break;
        }
    }
 
    --span; // Last span is one too high, because was not completed
 
//    log(total_correct,"total_correct_digit_span_forward");
//    log(span,"span_digit_span_forward");
//    log(span*total_correct,"kessels_score_digit_span_forward");
    var t1 = now();
//    log(t1 - t0,"timing_digit_span_forward");    
    
    await(1000);
    text("You have a forward digit span of " + span + "

" + "Click on the space bar to exit the experiment"); awaitkey(' '); } function matches(correct,answer,type) { var i, score = 0; for (i = 0; i < Math.min(correct.length,answer.length); i++) { if (correct[i] === +answer[i]) { ++score; } } return score; } function get_answer(time_out) { var i, digits_answer = [], local_blocks = [], e; feedback = addblock(6,65,90,10).align('left').style('font-weight','bold'); correction = addblock(70,65,10,10,"lightgrey","C").style('cursor','pointer'); ok = addblock(85,65,10,10,"grey","OK").style('cursor','pointer'); local_blocks.push(feedback); local_blocks.push(correction); local_blocks.push(ok); correction.on('click',function() { if (digits_answer.length) { digits_answer.pop(); feedback.text(digits_answer.join(' ')); } }); for (i = 1; i < 10; i++) { width = 8; margin = 2; b = addblock(6 + (width + margin)*(i-1),80,width,width,"lightgrey",i); var obj = {it: i}; var f = dojo.hitch(obj,function() { digits_answer.push(this.it); feedback.text(digits_answer.join('  ')); }); b.on('click',f); b.style('cursor','pointer').style('color','black'); local_blocks.push(b); } e = ok.await('click',time_out); if (e.type === 'timeout') { alert('Het is de bedoeling dat u alle cijfers aanklikt die zojuist werden getoond in dezelfde volgorde.'); ok.await('click'); } if (digits_answer.length === 0) { alert("Het is de bedoeling dat u eerst de cijfers aanklikt die zojuist werden getoond en dan pas op OK klikt."); ok.await('click'); } for (i = 0; i < local_blocks.length; i++) { main.removeblock(local_blocks[i]); } return digits_answer; }
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