Introduction
| If needed, there is also a reverse digit span task on PsyToolkit |
The digit span task is an absolute classic for anyone interested in short term memory. The basic idea of this task is this:
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A person is presented with a sequence of two digits
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The person needs to repeat the sequence
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If the person can do step 2 correctly, a longer sequence is presented
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This goes on until the person can not longer repeat the sequence
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The longest remembered sequence is the person’s digit span
It is often said that the average person can remember seven digits. This goes back to the work of George A. Miller, as you can read here on Wikipedia.
There are variations on this task. In the current implementation, the sequence length is only increased after the participant has remembered the same length at least two times. This makes the digit span measure more reliable.
Much has been written about the digit span task. It is discussed what it exactly measures (Jones & Macken, 2015).
About this implementation
The digit span task shows some really nice PsyToolkit features. It uses array functions, it works with the mouse only, and so on. Compared to most other experiments, the code looks somewhat more complex. This is mostly because of the way the participants enter the remembered sequence. Even so, it is fairly straightward. Even if you do not understand the code completely, it should be easy to modify.
| This demo can maximally measure of 9 digits. There are in total ten digits on screen, but if a person knows nine digits, the 10th digit will always be known (because it is the only remaining digit to choose from). |
The test stops when people make two mistakes in a row or if they have reached the maximum of nine digits.
Run the demo
Data output file
| In PsyToolkit, the data output file is simply a textfile. The save line of the PsyToolkit experiment script determines what is being saved in the data output file. Typically, for each experimental trial, you would have exactly one line in your text file, and each number/word on that line gives you the information you need for your data analysis, such as the condition, response speed, and whether an error was made. |
The data output is other than in most experiments. In this experiment, there are multiple lines per trial. The reaction time, exactly digit sequences presented and entered are saved. If you are only interested in the ultimate digit span, you can just look at the second number of the last line.
| If you embed this experiment yourself, make sure to set only the following two parameters in the analysis section of your experiment as follows: |
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Which column has dependent variable? set to value 2
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Only include last n lines set to value 1
Make sure not to fill in any of the other parameter boxes. This way, the data analysis will only look at the last line of each experiment data file, which contains the participants' best score. There is much other interesting information in the data files. If you really one, you can download all those files to your own computer and analyze further with your own script. But that is not necessary to take out the digitspan result.
PsyToolkit code
Click to expand the PsyToolkit script code (part of zip file below)
options
mouse on
bitmapdir stimuli
scale
fonts
normalfont arial 18
bigfont arial 28
bitmaps
digit1 # 1
digit2
digit3
digit4
digit5
digit6
digit7
digit8
digit9
digit0 # 10
##
continue_button
continue_button_dark ## for after being clicked
clear_button
mask
# -- instructions ------------
i1
i2
i3
i4
backButtonImage
nextButtonImage
startButtonImage
## important variables:
## &spancounter : the number of trials WITHIN a span (maximally 3)
## &spancorrect : the number of correct trials WITHIN a span (maximally 2, need 2 to continue)
## &actualspan : the max number someone remembered
######################################################
task digittask ## starts with 2 and then goes up every correct 2
## Step 1: Create random number sequence
set &&allNumbers range 1 10 ## from the bitmaps
set &&numberSequence sample &testspan from &&allNumbers
## Step 2: Start screen with basic instruction to get ready
font bigfont ## use big font for following two texts
show text "Memorize digits" #1
delay 1000
clear -1
show text "Get ready now!" #2
delay 800
clear -1
font normalfont ## back to smaller font for rest of texts
## Step 3: show all digits at 800 ms per digit
set $tmp_counter 1
while $tmp_counter <= &testspan
show bitmap &&numberSequence[$tmp_counter] #3
delay 800 ## how long each to-be-memorized digit will be shown
clear -1
set $tmp_counter increase
while-end
#
# Step 4: show the possible clickable digits and other buttons
#
show bitmap continue_button 250 250
set $range_begin show-counter
show bitmap clear_button -250 250
set $clear_counter show-counter
#
show bitmap digit1 -150 -250
show bitmap digit2 0 -250
show bitmap digit3 150 -250
#
show bitmap digit4 -150 -160
show bitmap digit5 0 -160
show bitmap digit6 150 -160
#
show bitmap digit7 -150 -70
show bitmap digit8 0 -70
show bitmap digit9 150 -70
#
show bitmap digit0 0 20
#
show rectangle 0 100 350 5 255 255 0 ## vertical "line", looks nice
#
set $range_end show-counter
#
# Step 5: Now let participant click the digit sequence from memory
#
set &&mask_stimuli clear ## for keeping track of masks overlayed on stimuli in virtual keyboard
set &&range_array range $range_begin $range_end ## so that we can later remove already clicked items from it
set &&digits_chosen clear
set &&already_done clear
while $finish_selection == 0 ## loop until continue button clicked
readmouse l 1 99999 range &&range_array
set &&clickedStimuli append UNDER_MOUSE ## store for later save
set &&rts append RT ## store for later save
if UNDER_MOUSE == $range_begin ## continue button was clicked
set $finish_selection 1
show bitmap continue_button_dark 250 250 # cover over continue button
show bitmap continue_button_dark -250 250 # cover over clear button
fi
if UNDER_MOUSE == $clear_counter ## clear button clicked
set $position_counter decrease 1
set $last_digit &&digits_chosen remove last
set $tmp &&range_array_removed remove last ## these values were stored
set &&range_array append $tmp ## increase range array
## now remove last mask drawn and last digit underneath
set $last_mask &&mask_stimuli remove last
set $last_digit &&digitsUnderStimNums remove last
clear $last_mask
clear $last_digit
fi
if UNDER_MOUSE > $clear_counter ## a digit button was clicked
set $position_counter increase
set &&range_array remove value UNDER_MOUSE ## remove so it cannot be clicked again
set &&range_array_removed append UNDER_MOUSE ## the removed values need to be saved in case you want to undo this action ("clear")
set $clicked_stimulus_x getx UNDER_MOUSE
set $clicked_stimulus_y gety UNDER_MOUSE
show bitmap mask $clicked_stimulus_x $clicked_stimulus_y ## mask the digit
set $tmp_mask show-counter
set &&mask_stimuli append $tmp_mask ## keep track of the mask stimuli in case removal needed
## now show red circle on the digit button that was clicked
show circle $clicked_stimulus_x $clicked_stimulus_y 20 255 100 100
delay 100
clear -1
##
set $myIndex expression UNDER_MOUSE - $clear_counter ## this makes the digits go from 13 to 22
## was this digit clicked before
set $already_done &&digits_chosen locate $myIndex ## check if digit was already clicked before
if $already_done == 0 ## if not already clicked (each digit is only used once in sequences)
set &&digits_chosen append $myIndex
set $xPosDigits expression $position_counter * 60 - 300
show bitmap $myIndex $xPosDigits 150
set &&digitsUnderStimNums append SHOW_COUNTER
fi
fi
while-end
#
# Step 6: Save detailed trial data
#
save BLOCKNUMBER "clickedStim" &&clickedStimuli
save BLOCKNUMBER "rts" &&rts
#
# Step 7: digit entry done, check if sequence was entered correctly
#
if &&digits_chosen == &&numberSequence
set $error_status 0
save BLOCKNUMBER &best_so_far &testspan $error_status "//" &&numberSequence "//" &&digits_chosen
set &spancorrect increase
show text "CORRECT" 0 70
if &spancounter < 3
set &spancounter increase
fi
if &spancorrect == 2
set &spancounter 0
set &spanerror 0
set &spancorrect 0
set &best_so_far &testspan
set &testspan increase
fi
fi
if &&digits_chosen != &&numberSequence
set $error_status 1
save BLOCKNUMBER &best_so_far &testspan $error_status "//" &&numberSequence "//" &&digits_chosen
set &spanerror increase
if &spancounter < 3
set &spancounter increase
fi
show text "WRONG" 0 70
fi
delay 2000
set &&clickedStimuli clear
set &&rts clear
#
# end task when 2 errors in row
#
if &spanerror == 2
set &digitspan &testspan
end tasklist
fi
# end task when digitspan is going to 11
# this is unlikely to happen, though
if &testspan == 10
end tasklist
fi
######################################################################
## blocks
######################################################################
block training
pager option mouse backButtonImage -250 220 nextButtonImage -30 220 startButtonImage 250 220
pager i1 i2 i3
set &testspan 2
tasklist
digittask 1
end
block digit_block
message i4 mouse
set &testspan 2
set &spancorrect 0
set &spanerror 0
set &spancounter 0
tasklist
digittask 99
end
feedback
text 0 -200 "Your memory score is the sequence you could remember 2x in a row."
text 0 -100 &best_so_far ; prefix "Your best sequence (digit span): "
text 0 100 "Click the mouse anywhere to continue"
wait_for_key mouse
endDownload
| If you have a PsyToolkit account, you can upload the zipfile directly to your PsyToolkit account. Watch a video on how to do that. If you want to upload the zipfile into your PsyToolkit account, make sure the file is not automatically uncompressed (some browsers, especially Mac Safari, by default uncompress zip files). Read here how to easily deal with this. |
Further reading
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Jones, G. and Macken, B. (2015). Questioning short-term memory and its measurement: Why digit span measures long-term associative learning. Link: https://www.sciencedirect.com/science/article/pii/S0010027715300354