Please help with my paradigm

[Anthony Haywood]

Dear all,

As a new member of this forum, I am not entirely sure that I am posting this in the right place but, here goes...

I am writing a paradigm to present the Mackworth clock task to a number of subjects. The paradigm itself consists of a circle of 59 grey dots and one white dot. The white dot moves around the circle, clockwise, as the second had on a clock would do, moving once per second.

The task is designed upon 60 pictures which are shown in sequence, ie picture one is the white dot at 0, I then rotated the picture 6 degrees and saved this as picture 2 and so on.

What I need to do is present the pictures in sequence but I want to radomly 'skip' one number so on occasion the 'second-hand' skips a notch anbd moves 12 degrees. I am unsure how to do this and any help would be greatly appreciated.

Many thanks in anticipation.

Anthony Haywood
Neurophysiologist