by psykinematix » Thu Feb 03, 2011 1:04 pm
The expression '0:360(360)' does not specify a value for a variable (it should be only used to specify the time-varying properties of a stimulus parameter). You should instead define an independent variable (named for example 'dir') with 2 random values (using the format '-1,1' where -1 would specify a left motion and 1 a right motion), then use 'dir' as the decision variable in the procedure panel ("correlated with expression" column) and -1 and 1 as the decision values ("Value" column) for the left and right choice inputs. If your stimulus is a vertical Gabor, to specify its motion simply set its phase to '0:360(360)' and its orientation to '90*[dir:1]' : it will drift to the right when the 'dir' takes the value '1' and to the left when it takes the value '-1'.
Have a look also at the following demo in the 'Storage' area:
Demos, Examples & Tutorials 1.2 / Experiments / RDK / Contrast Threshold / Staircase
It is using RDK instead of a Gabor but the experiment design is very similar to yours.
Hope this helps!
-- The Psykinematix Support Team