Move trhough a list forward and backward

[Eric at ericwalden.net]

I have an experiment with a list object and I would like to move both 
forward and backward through the list depending on the keyboard input. In 
other words, a 1 moves backwards and a 2 moves forwards in the list. Below 
is the code I have that is not working. This occurs after I display the 
list item, so the list index has already advanced from 0 to 1. First, I get 
the current index (which works fine) then I check to see if it is greater 
than 1 (i.e. 2 or more) because I can't go backwards if I am at the first 
item. If the response = 1 then I set a new variable called NewIndex which 
is the currentindex -2 (because it has already advanced). 

Then I try to set the attribute value back to the new attribute value. But 
for some reason, that does not work.

*How can I manually set the index of the current list?*

' My list is called ListOfComputers, and it is a list of computers (the 
task is computer shopping and subjects need to be able to move back and 
forth

CurrentIndex = c.GetAttrib("ListOfComputers")

'Check to make sure we are far enough along the list to move backwards
if CurrentIndex > 1 then
   if ShowMovie.RESP = 1 then
'Use -2 instead of minus one because the in line code occurs after the 
presentation slide so the list index has already advanced one space
     NewIndex = CurrentIndex - 2
     c.SetAttrib "ListOfComputers", NewIndex
   end if
end if

' This message box shows all of the variables with the values I want, it 
just does not actually change where on the list the next stimuli occurs.  
In other words it just keeps running through the list in the predefined 
order
msgbox("CurrentIndex = " & CurrentIndex & " NewIndex = " & NewIndex &" 
ShowMovie.RESP = " & ShowMovie.RESP)

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