Random ISI

[ftornay at ugr.es]

> Dear all,
> we would like to vary our interstimulus interval (ISI) randomly during the
> 
> experiment. We can't see any simple solution to this problem without the 
> stimuli being coupled in a fixed manner to a certain ISI. Have you got 
> any suggestions?
> Thank you very much for your support
> Dirk

In our lab, we have done something similar. If you only want the ISI to change 
so that subjects cannot predict when the new trial will begin, I think the 
easiest way would be this:

a) Insert a text display object (or similar) to be used as the ISI (let's call 
it ISI), set the duration property to any value, it won't make any difference. 

b) BEFORE the object, insert an inline with the following code:

'Choose a random ISI between a minimum and a maximum value (change as desired)
dim lngRandomISI as long
lngRandomISI = random(10, 1000) 'Between 10 ms and one second

'Set the duration of the ISI to the random value
ISI.duration = lngRandomISI

'Log the randomly chosen duration to the data file, in case you need it later
c.setattrib "ISIduration", lngRandomISI


Hope this helps

Francisco Tornay
Departamento de Psicología Experimental y Fisiología del Comportamiento
Universidad de Granada
SPAIN