How to present the sti at a presentation location in a same list?

[Francisco Tornay]

At 01:03 13/10/04, you wrote:
Dear colleague:

I have a set of sti presenting in the center of the monitor. Now I would
like to randomly present them either at the right or left side from the
center.
How should I do it? Is there some kind of function in E-prime that I can
use to assign different presenting locations to different sti (the sti are
in a list)?
Thanks!

Yung-Chi Sung


Hi, Yung-Chi (Is that your first name? Excuse me for my ignorance)

I'm not completely sure whether this has already been answered (I've had 
some problems with my E-mail). Just in case, here is how I've done what you 
are trying to do.

There is no special function in E-prime. You can do it as you usually 
change any aspect of your experiment: by using attributes. In what follows 
I use double quotes to refer to properties, attributes and values. Don't 
write the quotes.

In the object that presents your stimuli  use the properties at the "frame" 
tab. These properties determine a "frame" or rectangular area around your 
stimulus and allow you to locate it at different points. There are a few 
ways to do it, but here is a simple one which will work as long as you use 
a single stimulus at the same time. Otherwise you will have to changen 
other properties (width, height, maybe Xalign):

a) At the list that controls your trial procedure add a new attribute named 
"StimulusPosition"
Set the attribute to the value "25%" on the trials where you want your 
stimulus to appear on the right.
Set it to the value "75%" when you want it on the left.
Set it to "50%" when you want it centered.

b) Go to the properties of the object that presents the stimuli. Choose the 
"frame" tab. Set the X property at the "position" group to 
"[StimulusPosition]" so that it changes according to the attribute on the list.

This will change the position of your stimulus. You may want to experiment 
with some other values. For instance, you may need to set the "Clear after" 
property at the "General tab" to "Yes" if previous stimuli do not get 
deleted by other objects. More important, you may want to use other values 
instead of "25%" and "75%" if you want to move your stimulus more to the 
left or more to the right. In this case, note that values with the "%" 
symbol at the end refer to percentages of the screen (0 to 100) and simple 
numbers refer to number of pixels (0 to screen width). In both cases 
decreasing the figure moves the stimulus to the left and increasing it 
moves it to right.

I hope this helps.

Cheers



Francisco J. Tornay
Universidad de Granada
España