Cumulative response time from multiple sources in a single trial

[Joe]

Hello all,

I'm currently setting up a preferential looking study in which infants
will be presented with various pictures on two different screens and
their looking time at each picture type will be calculated. There will
be approximately 25 trials in which 2 pictures will be simultaneously
presented for 10 seconds on 2 screens (1 picture per screen). We are
interested in the total amount of looking time towards either of the 2
pictures within each individual trial, for each of the 25 trials.
Looking times will be recorded using "Playstation"esque controllers,
with which I've had no problems interfacing with Eprime.

It is likely that infants will spend time within each trial looking
back and forth between the two picture types. Coders are trained to
press one specific button on the controller if the infant is viewing
the screen on the left, and another specific button if the infant is
viewing the screen on the right (the screens are separated such that
it is obvious which of the two screens the infant is viewing). So, in
order to calculate the cumulative amount of time spent viewing each
picture, e-prime will need to keep track of the total amount of time
that either of the two buttons was depressed within each trial and sum
these values for each button.

I've begun by creating 2 variables (one for each button that
represents which screen the infant is viewing) as Summation objects
(e.g., Dim OneDuration as summation; Dim ThreeDuration as summation)
in the User Script. Next, in the experiment procedure I've placed an
Inline script to initialize both of the new variables as new
summations (e.g., Set OneDuration = New Summation; Set ThreeDuration =
New Summation). The Pictures are displayed following this Inline
object, which is in turn followed by a second Inline object with which
I want to calculate the total amount of time that either of the two
buttons on the controller were depressed. This is where I'm having
trouble.

I'm assuming that e-prime will need to keep track of the onset and
offset time for each of the two buttons (i.e., objects) within each
trial, then subtract the onset from the offset after the button has
been released, then, if there are multiple instances of a button being
pressed and released within a single trial, sum these amounts for each
button after the trial has completed. The problem is, I'm a bit unsure
of how to do this. Any ideas?

I appreciate all of your help with this!

Best Regards,

Joe B.

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