varying lengths of exposure based on responses

[Paul Gr]

Hello Scott,
one way of doing this is the following (I assume you already have a simple script for displaying the stimuli):
 
Add the following declarations to the gloabal user script (menu-view-script-user tab):
 
Const ExposureDelta% = 1000Const ExposureLowLimit% = 1000Const ExposureHighLimit% = 20000
dim iExposureTime as longdim strPrevResp as string
Then, insert an inline script object to initialize the global iExposureTime variable (this would normally be at the start of a block):
 
iExposureTime = 8000
Then, insert an inline script just before the image object (called Stim in this example) to set the exposure time of the simulus object:
Stim.Duration = iExposureTime
 
Finally, insert an inline script after the stimulus object to check the response and modify the exposure time:
 
' get the response
Dim t as stringt = LCase$(Stim.RESP)
 
' check response and alternation
if t="n" And strPrevResp<>"n" Or t="m" And strPrevResp<>"m" then   iExposureTime = iExposureTime + ExposureDeltaelseif t="z" And strPrevResp<>"z" Or t="x" And strPrevResp<>"x" then   iExposureTime = iExposureTime - ExposureDeltaend if
 
'check upper and lower limits
if iExposureTime<ExposureLowLimit then   iExposureTime = ExposureLowLimitelseif iExposureTime>ExposureHighLimit then   iExposureTime = ExposureHighLimitend if
 
' remember the response to check for alternation
strPrevResp = t
 
You might consider removing the alternation test (and related code) and only use two keys because eprime will not generate repeating key presses when the key is hold-down. (Authorware will!) 
 
Hope this helps,
 
Paul Groot
VU University, Amsterdam
 



> Date: Fri, 20 Apr 2007 11:22:48 -0400> From: smoeller at umich.edu> To: eprime at mail.talkbank.org> Subject: varying lengths of exposure based on responses> > Dear Colleagues,> > I'm fairly new to using e-prime, and I'm hoping someone can help me out > with a question.> > A somewhat recent paper (Aharon et al., 2001) describes a task in which > participants are exposed to faces. The catch is that participants > could vary the amount of exposure they had to these faces by their > responses. The default length of exposure was 8s. If they wanted the > faces to disappear faster, they could alternate pressing the "z" and > "x" keys. However, if they wanted the pictures to remain on the screen > for longer than 8s, they could alternate pressing the "n" and "m" keys.> > The authors used Authorware (Macromedia) for this task. I was > wondering if a similar task could be performed using e-prime.> > Thank you for your time!> > Best regards,> > Scott Moeller> University of Michigan> 
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