The Neurofeedback Dialog

The Neurofeedback Dialog

The Neurofeedback dialog allows to select the data from one or more channels as the source of feedback information for a subject during an ongoing measurement. It is also possible to select the output of a running SVM classifier as a neurofeedback signal. Besides defining the data source for feedback, the dialog also allows to create different visualizations that can be presented to a participant during neurofeedback training. The signal from channel(s) or SVM output can be presented as a thermometer display to the subject (see below).

Values for neurofeedback are calculated by subtracting the last baseline (BL) from the current scaled oxy/deoxy value. Note that deoxy values are inverted so that a negative deflection results in a positive feedback signal. In detail, the calculations are as follows:

For oxy: (oxy_value - last_oxy_BL)
For deoxy: -1*(deoxy_value - last_deoxy_BL)
For the combineddata: 1/2*((oxy_value - last_oxy_BL) - (deoxy_value - last_deoxy_BL)).

The resulting values are scaled to a level of the thermometer for display in relation to the “Max Val Oxy” and “Deoxy” values that can be changed in the Neurofeedback dialog.

As default, oxy and deoxy neurofeedback values are stored in text files - one for each time point - in a sub-folder called “NeurofeedbackValues”, which is placed within the folder containing the specified protocol (.prt) or header (.hdr) file. Each text file is named “Feedback-.txt” and contains 7 values: the pre-condition oxy-baseline value, the oxy feedback value, the calculated oxy level (integer) specifying the filling of the thermometer, the pre-condition deoxy baseline value, the deoxy feedback value, the calculated deoxy thermometer level, and a value specifying the current condition as an index value. If export of numerical values is not needed, turn off the “Export numerical values to disk” option in the “Neurofeedback” dialog.

The feedback images (thermometer) can also be saved - one for each time point. The image files are located in a sub-folder (“NeurofeedbackImages”) of the folder where the protocol was selected from. Images are NOT saved as default - to use this option, you need to turn on the “Export image snapshots to disk”. The images will be saved as PNG files with the naming pattern “Feedback-.png”.

The duration of the instruction display can be specified in seconds.

Feedback is now always shown in all conditions (including baseline) as default. Turn on the “No Feedback Condition” option in the “Feedback baseline data points” field in the Neurofeedback dialog if you do not want to show neurofeedback to the subject during baseline (usually preferred).

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