implement change blindness flicker paradigm

[David McFarlane]

Melissa,

Stock reminder:  1) I do not work for PST.  2) PST's trained staff 
takes any and all questions at 
http://support.pstnet.com/e%2Dprime/support/login.asp , and they 
strive to respond to all requests in 24-48 hours (although current 
estimates are more like 10 days) -- this is pretty much their 
substitute for proper documentation, so make full use of it.  3) If 
you do get an answer from PST Web Support, please extend the courtesy 
of posting their reply back here for the sake of others.

That said, here is my take...

Yes, that is possible, to a point.  However, if you use an input mask 
on the Slide and just rapidly re-run that Slide, you will have some 
trouble with RTs.  That is because the input mask will not be armed 
in the short intervals between each running of the Slide object, and 
if a response comes in during those intervals then it will be 
missed.  And the more rapidly you cycle through your Slide, the 
greater the effect.  (I know, because I ran into this with an 
experiment a few years ago.)

For something like this, better to use "extended response" (see 
Appendix C of the User's Guide that came with E-Prime).  Implement 
your flicker loop however you like, and just before your flicker loop 
add a Wait object.  Set its Duration to 0, give it an appropriate 
input mask, and set the Time Limit to (infinite), or a time limit 
that you choose.  Set End Action to Terminate or (none), as seems 
appropriate.  Now the input mask from the Wait object will run over 
all the iterations of your flicker loop and will catch a response at 
any time.  If you want the flicker loop to then react to the 
response, use some inline code such as (assuming you name your Wait 
object RespWait)

If Not(RespWait.InputMasks.IsPending()) Then ...
If RespWait.RT <> 0 Then ...
If RespWait.RTTime <> 0 Then ...
If RespWait.RESP <> "" Then ...

Finally, given that the Wait object takes care of getting the 
response, I would probably dispense with the two-state Slide (which 
requires even more inline code) and just use a pair of ordinary 
stimulus objects for the flicker loop.

-- David McFarlane, Professional Faultfinder


>I am trying to implement the classic flicker paradigm for a change
>blindness study.  I would like to oscillate between a picture and its
>mask for 40 seconds or until a participant hits a button.  I think the
>best way to do this would be to use one slide object and oscillate
>between slide states (1 state for the picture, 1 state for the mask)
>in order to keep track of RT for the user response.  Is this possible?
>
>Thank you,
>Melissa

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