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Appendix A: Using the EyeLink 1000 Plus Analog and Digital Output
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2013-2017 SR Research Ltd.
The onset of the strobe is also delayed from the time that analog outputs
change, in order to allow outputs to settle to the new voltages. A delay of 400
microseconds is standard, allowing the use of signal-conditioning low pass
filters as discussed earlier.
7.6.2 Oversampling and Toggle Strobe
Another possibility is to over sample the analog output, by recording the analog
outputs at more than twice the EyeLink 1000 Plus sample rate. This will
prevent missed samples, but will still result in steps in the data. Recording the
digital strobe output (on an analog or digital input channel) in combination with
the analog data allows the first data from each sample to be selected, by
detecting the change in value of this output. By setting the duration of the
strobe pulse to 0, the strobe output can be set to toggle between high (4 to 5
volts) and low (0 to 1 volt) for every sample, which produces the best signal.
Over sampling can also be used without the strobe when the analog data is
being used to drive a gaze-contingent display, as the time of each sample is
unimportant and over sampling will minimizes total data delay.
