synchronize event markers with refresh rate

[Paul Groot]

Hi Hank,

The OnsetSignal-properties can only address one IO-port at the time
(all 8 bits at the same time because there is no masking mechanism).
Using any kind of handshaking just complicates the one-way digital
interface. However, if you still would like to use a separate strobe
signal, you could use the WritePort function in an inline just before
the stimulus object to set/prepare the 8 data-pins. Then configure the
OnsetSignal properties to generate the time-critical strobe signal, so
it 'triggers' at stimulus onset. However, the OnsetSignal properties
cannot write individual bits of the control register (C0), so this
might complicate things a bit if other bits of the control register
should be preserved. Also note that this wouldn't work if the duration
of the strobe is critical and is different from the stimulus duration.

The markers that have to be generated for responses are indeed
different. In most cases these markers can be generated with the
writeport function after termination of the stimulus object. Because
of this, these response markers will not be exactly in sync with the
actual response (i.e. it takes time in eprime to handle the response,
terminate the object and start the inline script). There are two
possible workarounds if the timing of response markers is very
critical: 1) use special hardware to detect responses and route it
digitally to both the eprime system and the second system. 2) apply an
off-line correction by using the stimulus-onset marker and the
(accurate) RT recorded by eprime to insert response markers at the
right places in the acquired data. However, my guess would be that the
touch responses are not detected very accurately anyway, so simply
using writeport would be sufficient in this case. (You could simply
estimate the delay by comparing the RT values recorded by eprime with
the time differences of the stim/response markers.)

best,
Paul


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