Eprime Newbie-- need help with inspection time

[Bpesta22 at cs.com]

Help with inspection time.

Greetings.

I am interested in using the inspection time task uploaded onto the eprime 
website by Paul Groot. I'm having two problems (and I am not at all versed in 
programming) that I was hoping someone here could help me with.

1) The experiment is written for 100hz monitors. I only have access to 
machines with 60hz monitors. As far as I can tell from the code, it seems like 
running in 60hz would be do-able, but I lack the expertise to know if the 
experiment would still produce reliable data running at 60hz.

2) There's a section of the code that I cannot grasp. Briefly, in the 
inspection time task, two lines are presented, and the subject decides which one is 
longer. The lines remain on screen only for a short period of time. The 
duration for the next trial changes whenever a "reversal" occurs. For example, if the 
subject gets 4 right at the current duration, a reversal occurs, and the 
duration time is decreased (making the task more difficult) by a set amount for 
the next trial. Conversely, if the subject gets this trial wrong, a reversal 
also occurs, and now the duration time for the next trial is increased.

The duration time for any trial is just the refresh interval of the monitor 
(10 ms for 100 hz, or 16.67ms for 6 hz, as with my monitor) x the number of 
frames.  For example, the first trial has 10 frames, so the stimulus remains 
onscreen for 100ms (100hz) or 167ms (60hz). If the subject gets 4 right at this 
duration, the number of frames is "stepped down" by 4. So, the next trial would 
have 6 frames and the stimulus would last for 60ms. The step sizes decrease in 
later trials to hone in on the subjects true "inspection time".

When I run myself as a subject, though, the data file seems off. Sometimes 
when I do 4 right at a given duration, the number of reversals does not go up by 
one (even though the next trial presents the stimulus at a shorter duration). 
Other times, 4 right at a given duration does result in a reversal.

The same is true with mistakes-- sometimes eprime will record the reversal, 
and the duration for the next trial will increase; other times, the reversal is 
not recorded in eprime, even though the next trial does have an increased 
duration. Here's the relevant (I think!) part of the code:

    if nOK>=REAVALUATE_CORRECT_COUNT then
        ' decrease stim duration
        nOK = 0 ' restart counting
        if (nPrevFrameCount < nFrameCount) then nReversals = nReversals + 1
        nPrevFrameCount = nFrameCount
        nFrameCount = nFrameCount - nStepSize
        if nFrameCount<=0 then 
            nStepSize = nStepSize \ 2
            if nStepSize<1 then nStepSize=1
            nFrameCount = nStepSize
        end if

The fourth line makes no sense to me. I have 4 correct trials in a row, so I 
should get a reversal (the next trial should present the two lines at a 
shorter duration). But how is it that the previous frame count could be less than 
the current frame count. Shouldn't it be the opposite (the previous frame count 
was higher-- the lines were displayed longer-- than the frame count for the 
current trial).

Sorry for the length of this post, perhaps I should stop here. If anyone 
could help, I would sincerely appreciate it.

Bryan

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listserv.linguistlist.org/pipermail/eprime/attachments/20061227/482fdeb0/attachment.htm>