Correcting RTs for positive SOAs (picture word interference)

[David Vinson]

Hello all,

I am wondering if anyone can help me out with a small design problem.  We
are carrying out a picture-word interference experiment, and are
manipulating SOA between the picture and word displayed.  We always want to
measure RT from the picture onset.

If SOA < 0, the word is displayed before the picture, if SOA > 0, the word
is displayed after the picture.  We currently use conditional branching to
determine the order in which these items are displayed, and collect RTs
from an empty "Wait" object that immediately follows the last-presented object:

(SOA < 0)
Word display for [-SOA] milliseconds
Picture display
"Wait" object until response is made

(SOA > 0)
Picture display for [SOA] milliseconds
Word display
"Wait" object until response is made

The problem is in the latter condition: RTs measured for the "Wait" object
underestimate the picture response latencies by (SOA) milliseconds.  Is
there a way to automatically correct these RTs in the datafile using an
inline object?  Or alternatively, is there an easy way to create a new
variable (e.g. CorrectedRT) which is logged to the datafile?

Thanks,
David Vinson
Dept of Psychology, University College London