The ATRIG_VAL variable is used to specify how to use an external analog signal to trigger the start of a paradigm. ATRIG_VAL is used when TRIG_FLAG is set and TRIGTYPE is 3, indicating that an external analog signal will be used for the trigger. The ATRIG_CHAN variable should be set to specify which analog channel is to be used as the trigger signal.

Analog voltage transitions that cross the ATRIG_VAL threshold will be considered trigger pulses. By default, either positive or negative transitions are recognized as triggers for starting the paradigm (TRIG_FLAG & 2). If TRIG_FLAG indicates that trigger pulses should be recorded throughout the paradigm, only positive transitions will be recorded.

See Also:
Trigtype, Atrig_chan, Atrig_val, Dstartmask)
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