Introduction

The Simon task and the Simon effect are named after J. R. Simon. Together with his colleague, he first described this effect in 1963. In essence, it shows that people respond faster and more accurately if there is a match between stimulus and response features (e.g., location, when for example stimulus and response are both located on the left side of one’s body).

The effect is also known as a stimulus-response compatibility effect. There are many variants of the stimulus-response compatibility available. Like the Stroop effect, it is easy to notice consciously how difficult a mismatch between a stimulus and response can be.

There is also a mobile phone friendly version. Click here

About this implementation

In this example, you need to respond to the words left and right with the a key (which is on the left side of the keyboard) and with the l key (which is on the right side of the keyboard). The Simon effect here simply means that you will respond more slowly to the word LEFT when it appears on the right side of the screen (i.e., incompatible condition) than when it appears on the left side (compatible condition) of the screen.

  • The Simon effect is here reported as the average response time in incompatible trials minus the average response time in compatible trials. Typically, this is around 35 ms.

  • Note, you can show your response times and copy and paste them to a local file for your own data analysis.

Run the demo

Respond to the word left witht the a key and to the word RIGHT with the l key.

The demo takes less than 2 minutes to complete.

Click here to run a demo of the Simon task

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.

Meaning of the columns in the output datafile. You need this information for your data analysis.

Colum Meaning

1

Tablerow number

2

position of the stimulus (left or right)

3

required response position (left or right button)

4

compatibility (compatible or incompatible)

5

Status (1=correct, 2=wrong, 3=timeout)

6

Response Time (ms)

PsyToolkit code

Click to expand the PsyToolkit script code (part of zip file below) 
options
  bitmapdir stimuli 

bitmaps
  intro
  finalwords
  left
  right
  fix
  mistake

fonts
  arial 18

table simontasktable # table with four rows, each trial one row is randomly chosen
#-name of condition--------------position--stimulus--response
  "left  leftresponse  compatible"     -200      left      1
  "right leftresponse  incompatible"    200      left      1
  "right rightresponse compatible"      200      right     2
  "left  rightresponse incompatible"   -200      right     2

task simon
  table simontasktable                   # table to be used
  keys a l                               # keys to be used
  show bitmap fix                        # show fix point at screen center
  delay 300                              # do nothing for 300 ms
  show bitmap @3 @2 0                    # show imperative stimulus
  readkey @4 5000                        # wait for key response up to 5 seconds
  clear 1 2                              # remove stimuli
  if STATUS != CORRECT                   # if you make an error
    show bitmap mistake                  # show an error message at screen center
    delay 1000                           # for 500 ms
    clear 3                              # and then clear
  fi                                     # end of if statement
  delay 500                              # wait 100ms (here sort of intertrial time)
  save TABLEROW @1 STATUS RT             # save data to file

message intro

block test    # this block is called "test"
  delay 1000
  tasklist
    simon 30
  end
  feedback
    text align left
    set &RTCon mean c6 ; select ( c1 == 0 || c1 == 2 ) && c5 == 1 
    set &RTInc mean c6 ; select ( c1 == 1 || c1 == 3 ) && c5 == 1
    set &RTSimon expression &RTInc - &RTCon
    text -300 -200 "Average response speed in conditions (correct trials only):"
    text -300 -150  &RTCon ; prefix "Compatible: "   ; postfix " milliseconds"
    text -300 -100 &RTInc ; prefix "Incompatible: " ; postfix " milliseconds"
    text -300 -50  &RTSimon ; prefix "Incompatible - Compatible (Simon effect): " ; postfix " milliseconds"
    text -300 100 "Press space bar to continue"
  end

message finalwords

Download

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

Simon, J.R. and Wolf, J.D. (1963). Choice reaction times as a function of angular stimulus-response correspondence and age. Ergonomics, 6, 99-105.

Hommel, B. (1993). Inverting the Simon effect by intention: Determinants of direction and extent of effects of irrelevant spatial information. Psychological Research, 55, 270-279.

Prinz, W. & Hommel, B. (2002). Common mechanisms in perception and action: Attention and Performance, Vol. XIX. Oxford: Oxford University Press.