Difference: DocsSectionsBuildingExperiments (34 vs. 35)

Revision 3527 Feb 2015 - Main.PhilipVanDenBroek

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Building Experiments

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Trigger table

While actions give meaning to the events, the Trigger table implements the logic of the experiment program flow. It defines how each event possibly triggers the execution of other events. Conditional expressions implement runtime dependent triggered events, made possible by allowing global variables to be used in these expressions. An example would be to either trigger the next_trial event or next_sequence event based on the current state of the num_acquired_trials variable. Table 3 demonstrates corresponding Trigger table.
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marker time fire datasource delay condition
trial EVENT next_trial eeg 0 num_acquired_trials <= 10
trial EVENT next_sequence eeg 0 num_acquired_trials > 10
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marker time fire datasource delay condition triggeraction
trial EVENT next_trial eeg 0 num_acquired_trials <= 10  
trial EVENT next_sequence eeg 0 num_acquired_trials > 10  
-   print_output eeg 0 num_acquired_trials==10 mod
  Table 3: Trigger table
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As long as the number of acquired trials doesn't exceed 10, a next_trial event is triggered by the trial event, otherwise a next_sequence event is triggered. If no conditional expression is specified, corresponding event will always be triggered. Optionally, a delay can be specified, which value is default referenced relatively against the events timepoint time that triggers it. If it should be referenced against actual moment of execution of the event, instead specify for the delay: 0,'now'. The datasource is only relevant if corresponding triggered event defines data (it has a DATA timepoint) in order to collect the correct data epochs. For example useful if a single marker triggers periodic data collection or a limited number of data epochs as determined by logic incorporated in the conditional expression .
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As long as the number of acquired trials doesn't exceed 10, a next_trial event is triggered by the trial event, otherwise a next_sequence event is triggered. If no conditional expression is specified, corresponding event will always be triggered. Optionally, a delay can be specified, which value is default referenced relatively against the events timepoint time that triggers it. If it should be referenced against the actual moment of execution of the event, instead specify for the delay: 0,now. The datasource is only relevant if corresponding triggered event defines data (it has a DATA timepoint) in order to collect the correct data epochs. For example useful if a single marker triggers periodic data collection or a limited number of data epochs as determined by logic incorporated in the conditional expression.

Markers can also be triggered based on the state of the variables, i.e., watchdog triggered markers. Each time a global variable involved in the conditional expression is being modified, the conditional expression is evaluated and if true, corresponding marker is triggered. This is the default behaviour, however, the user can control which global variable(s) modifications and which actions ( mod, put, or mod and put) will start the evaluation of the expression. For instance: mod(num) means evaluate the expression only a mod-action for variable num. For watchdog triggered markers the marker information can be left empty or specify a dash -, the time column information can be left empty since triggering is not time-dependent.

 
 
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