[psychology-visionlist] Psychophysics question

[Jan Derrfuss]

Dear all,

I was wondering if someone might be able to help me with a psychophysics 
question. I would like to run an fMRI experiment involving a motion and 
a colour task. The exact design is still an open question, but I imagine 
something along the following lines: Stimuli would consist of moving 
grey dots and stationary coloured dots. In one set of blocks, 
participants would be instructed to attend to the moving dots. The task 
would be to detect occasional changes in the movement speed. In the 
other blocks, participants would be instructed to attend to the coloured 
dots. The task would be to detect occasional changes in the colour.

I would like to have an easy (e.g., 90% of changes detected) and a 
difficult condition (e.g., 50% of changes detected), and I would like 
these values to be as similar as possible for the motion and the colour 
task and across participants. So far, so good. Now, I suspect there 
would be little point in doing the threshold adjustment outside the 
scanner (as I would not expect a threshold identified on a monitor 
outside the scanner to carry over to the projection screen used inside 
the scanner). In the scanner, however, time is money, and even if I ran 
a thresholding procedure during the anatomical scans, there would likely 
not be more than 10 minutes available. My question: Do I stand any 
chance of achieving what I would like within 10 minutes or so?

Any input would be very much appreciated.

Cheers,
Jan


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Dr. Jan Derrfuss
School of Psychology
University of Nottingham
University Park
Nottingham NG7 2RD

Email: jan.derrfuss at nottingham.ac.uk
Phone: +44-115-84 67920
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