display refreshing in tobii eyetracking extensions for eprime?

[Michiel Spape]

Hi Adam,

It's been a while since I last worked with the Tobii, so I might be wrong here, but I think it's unlikely it has anything to do with the monitor's refreshing. First, the monitor always refreshes in a fixed number of hz, I've never heard of anything you can do to stop this updating entirely, even though you can typically change the number of refreshes in system>control panel>display options>hardware (or something like that) - but less than 0.3 Hz (given your stimuli's duration): forget it. Obviously, you normally wish to sync your stimulus presentation with refreshes (that's the common problem), which you can set in E-Prime (onset sync, etc). Second, the Tobii output when it doesn't know where a subject is looking (either because of the subject moving a lot, the subject blinking, or hardware problems) is also -1. Ask your subject not to blink too much might be the best course of action. You might also want to change the sample-rate of the Tobii - ours could go to 120 Hz, but its output at higher sample-rates (>80 Hz) wasn't too brilliant. 

Anyway, Tobii gives validity markers for time-points in which the output can or cannot be trusted - see documentation - I expect your "-1" output is probably also marked as invalid. Just delete the invalid data.

 

Hope this helps.

Mich

 

Michiel Spapé

Research Fellow

Perception & Action group

University of Nottingham

School of Psychology

 

From: e-prime at googlegroups.com [mailto:e-prime at googlegroups.com] On Behalf Of Adam Osth
Sent: 10 November 2009 22:46
To: e-prime at googlegroups.com
Subject: display refreshing in tobii eyetracking extensions for eprime?

 

Hello all,

I'm currently running EPrime 2.0 with extensions for Tobii for eyetracking. I have this problem where in the data, every trial seems to have a couple of points in which "-1" is returned for the fixation location. I've heard that this is caused by the display refreshing after a certain amount of time. Is there any way to control when the display refreshes so it won't do that when a stimulus is being presented?

It should be noted that my stimuli only display for 4500 ms, so it doesn't have to refresh while the stimulus is up.

Adam



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