FAQ: How can I accurately keep track of reaction times (RTs) for participant responses?

[SR-SUPPORT]

Calculating a reaction time (RT) in Experiment Builder is a simple process of subtracting the stimulus onset time from the response time. The basic formula is:
Reaction Time = Response Time - Onset Time

As shown in the image, a clear way to implement this is to use an UPDATE_ATTRIBUTE node to store each time in a separate variable before calculating the final RT.

   

1. A variable named KEY_RESPONSE_TIME is used to store the response time from Keyboard_Input.triggeredData.time (Response Time).
   
2. Another variable, Display_On_Time, is used to store the onset time from DISPLAY_SCREEN.time (Onset Time).
   
3. A variable named KEY_RESPONSE_TIME is used to store the response time from Keyboard_Input.triggeredData.time (Reaction Time).
   

The Stroop project (File menu > Examples) provides a working example of this process.

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⚠️ Important Warning: Do Not Use .startTime
The .startTime property records when a node was entered, not when it was executed. Due to pre-loading and screen refresh cycles, this is not the true stimulus onset time. It should NOT be used for RT calculations.