‍Varying Exposure Time or Time Limit for Participants to Respond

‍Summary

‍The time limit feature in the Event Editor’s Input tab can be a fixed value or a variable one. This is useful for varying the exposure duration of visual stimuli, or to vary how long participants have time to respond.

‍Creating a Trial Level

‍The first step is to create a trial level; click on the Experiment menu and choose Trial Levels…; a dialog presents itself:

‍The dialog will look different if a trial variable or more already exists.

‍In this example, we want a time limit that varies between 1000 and 2000 milliseconds. Click on the Time Limit icon to create a trial variable:

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• Give the trial variable a name, e.g. “Time limit”.
• In the Levels tab, type in the values that you want, in milliseconds and separated by a comma. It is not possible to specify a range; you will need to provide the desired values within that range.
• By default, these values are randomized with no replacement; click on the Level Selection tab to change that.
• In the Options tab, we recommend that you provide a description.

‍Using the Trial Level

‍Once created, using the variable time limit is straightforward:

• Double-click on the event to edit it.
• Turn on the time limit checkbox.

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• By default, the time limit value is fixed. Click on “Fixed:” and select “Variable:” instead.
• If you have created more than one trial variable, you can choose which one to use.

‍Varying Short Exposures

‍If you are creating a variable time limit to vary the exposure time of a visual stimulus, make sure to read this support note, High Precision Presentation of Stimuli, especially if the exposure times are short, e.g. in the order of a few refresh cycles.