In polygraphy, the term refers to a specific aspect of a waveform, pattern or measurement in a tracing. Features are the fundamental components of chart interpretation on which scoring and decision rules depend. Currently there are about 12 individually validated manual scoring features. In the breathing channel they are: apnea, baseline increase, suppression, and increase in cycle time (slowing). For the electrodermal channel they are peak amplitude, complexity, and duration. In the cardiograph, the features are amplitude and duration. The finger plethysmograph relies on the duration and magnitude of the constriction of the pulse amplitude. Other features are sometimes taught as part of scoring systems, though their validity is disproven or absent. See: Kircher & Raskin (1988); Bell, Raskin, Honts & Kircher (1999).
