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Measuring reaction-time: How to know if results are accurate?

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I'm working on an AutoIt program that will be used in a psychological study to measure a person's reaction time.  I have a draft of the program completed, and it seems to work.  In other words, the reaction-time data is plausible.

The program displays a random digit between 2 and 8 inclusive (this is called the "target digit").  The user has to hit the corresponding key as quickly as possible.  The program measures the amount of time it takes the user to hit the key.  There are multiple trials per session, and an average reaction-time is calculated at the end of the session.

Here are the two critical AutoIt functions that perform the actual timing. (In the first function, I edited-out some lines of code that display the target digit in a GUI):

Func _PresentProblemAndGetResponse($sProblem, $sAnswer, $hGui)Local $iReactionTime
Local $iCorrect
Local $sLocalTime
Local $avResults[4]
[Edited-out the code that displays the target key in a GUI]
$hBegin = TimerInit() ; Start the stopwatch running
$iCorrect = _GetKeyPress($sAnswer) ; The parameter here is the correct answer (i.e., the solution to the problem). A returned value of 0 means user pressed wrong key; 1 means correct key.
$iDiff = Round(TimerDiff($hBegin)) ; Stop the stopwatch and get elapsed time in milliseconds
$iReactionTime = $iDiff ; This is the user's reaction time in milliseconds
$sLocalTime = _GetTime() ; This is the user's current local time
GUICtrlDelete($hLabelMessage) ; Erase the problem from the GUI
$avResults[0] = $sProblem ; Assign the relevant data to a vector
$avResults[1] = $iReactionTime
$avResults[2] = $iCorrect
$avResults[3] = $sLocalTime
Return ($avResults)
EndFunc   ;==>_PresentProblemAndGetResponse

Func _GetKeyPress($iRightAnswer)
Local $iRightAnswerCode = 30 + $iRightAnswer ; Convert the answer into the ASCII code that's required by the _IsPressed function
Local $iWrongAnswers[10] = [30, 31, 32, 33, 34, 35, 36, 37, 38, 39] ; Initialize array of wrong answer digits
$iWrongAnswers[$iRightAnswer] = '20' ; Replace the right answer with the code for the space character
While 1
For $x = 0 To 9
If _IsPressed($iRightAnswerCode) Then Return (1)
If _IsPressed($iWrongAnswers[$x]) Then Return (0)
EndFunc   ;==>_GetKeyPress


So, I have two questions.  The second question is much harder, I think.

First of fall, does my approach seem like a reasonable way to measure the time between displaying a target number and registering a user's keypress?  If not, what's a better approach?

Second, how can I verify that the results are accurate?  I've run the program over a hundred times (using myself as the subject), and the results are about what I would expect.  Actually, my main interest lies in measuring small changes that take place over the course of many sessions performed over weeks or months.  The absolute precision isn't terribly important, but consistency is very important.  In other words, if the results are high by 5%, that's not too much of a problem, as long as they are consistently high by 5%.

Thanks for considering my questions.


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Hi Alex, this could be a way to get the response time of a digit from the screen.


Global $Correct = False, $Counter = 1, $Max = 10, $Random, $Last, $Total

$hMain = GUICreate("Reaction Time Measure")
$hDigit = GUICtrlCreateLabel('',100,0,200,50,0x01)
$hResponseTime = GUICtrlCreateEdit('The test will display ' & $Max & ' digits, one digit each time. You have to press the button of the digit you see it.',0,200,400,150,0x0800)
GUICtrlSetFont($hDigit,30,900,1,'Arial Black')
$hButton = GUICtrlCreateButton("Start test",125,360,150,35)

While True
    Switch GUIGetMsg()
        Case -3 ;GUI_EVENT_CLOSE
        Case $hButton   ; Test will start

Func Test()
            $Random = Random(1,9,1)
        Until $Random <> $Last
        $Timer = TimerInit()
        Until $Correct
        $Diff = TimerDiff($Timer)
        $Correct = False
        $Counter += 1
        $Total += $Diff
        $Last = $Random
        GUICtrlSetData($hResponseTime,Round($Diff,3) & @CRLF,1)
    Until $Counter = $Max
    GUICtrlSetData($hResponseTime,"Average response time: " & Round($Total/$Max,3),1)

Func Correct()
    If @HotKeyPressed = $Random Then $Correct = True

Usually, native functions are faster then UDFs, so I like more this way. But if you still want to use _IsPressed be sure you open user32.dll and use the handle as second parameter of the function otherwise the dll will be opened every time you call the function. This may lead to different response time and for a test like yours this may be relevant.

My example is raw but can be improved to work as you like. Hope this was helpful in any way.

When the words fail... music speaks

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Hello AndreiK,

Thank you for the detailed answer.  I will try your suggestions this weekend.  For now, I'll mark the question as answered, although I think I'll eventually post again about my second question (regarding precision / accuracy in the results).

Thanks again.

-- Alex Chernavsky

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