Psychophysiological measures have in common with other types of biomarkers the fact that the unit of measurement is biological. They, like many other types of biomarkers, depend on a psychological task or circumstance; understanding the paradigm used to elicit the physiological response is thus critical to the interpretation of the significance of the response. The eye blink startle electromyographic (EMG) response takes on quite different meaning if it is elicited by an intense unexpected event, the same event when part of a pre-pulse inhibition sequence, and the same event presented while viewing pleasant or aversive imagery. In only the first two of these paradigms is the response heritable, and only pre-pulse inhibition receives strong support as an endophenotype (Anokhin, Golosheykin, & Heath, 2007; Anokhin, Heath, Myers, Ralano, & Wood, 2003; Hasenkamp et al., 2010; Malone et al., 2014). Psychological context is thus important to the evaluation of a psychophysiological marker, a fact that is often not fully appreciated when an electrophysiological signal is interpreted as a neurophysiological biomarker as though the bioelectric response itself is all that matters.
