help with attention probes

I have a quick question.

In one phase of my experiment, a series of 20 faces are presented; each face is on the computer screen for 10 seconds and there is a 6 second inter-stimulus interval between each face. This has been easy to set up.

Now I am trying to have an attention probe (e.g., a red cross-hair) appear at a random time on each face; I then hope to record the participants’ reaction time to the onset of the probe. In other words, I want a red cross to appear on the forehead of each face stimuli at a random time in the 10 second period in which each face is shown. However, I do not know how to make the probe appear or how to set up the timing.

In case you are curious, I am doing this because half of the faces have direct eye gaze and half have averted eye gaze. I want to verify that participants are paying attention to both types of faces equally; ideally, they would respond to attention probes on the direct gaze faces as quickly as the respond to the attention probes on the averted gaze faces,

If anyone can help, I would be very appreciative.


Well, the closest organization that comes to mind is as follows:

Configure the trials to be presented every 16 seconds (“End” tab in Trial Editor).

Event 1: 6 second ISI – should erase the screen
Event 2: Face with random time limit
Event 3: Probe – Time limit here is optional. Unfortunately, there’s no way to make this 10sec-Ev2, so any time limit will turn into Ev2+kEv3 if there is no response. If there is a response within your desired amount of time, then the 16 second interval on the trials will ensure that Ev2 is only visible for 10 seconds. The only problem comes up if there’s no response within the desired limit.

This is the closest to your requested behavior that I’ve been able to come up with.

I hope this helps.