Subjectively the possession of a role factor is felt as a 'mental set' which modifies all ordinary responses. The very same stimulus is perceived in a different way when one is in the role and when one is out of it... Technically, we handle this change of perception the same way in a role as in a mood—both of which can intrude on the ordinary personality — by this special factor, L, which can be called a modulator factor. A modulator factor comes into action only when the usual ordinary 'focal stimulus' comes into the orbit of a set of role cues which we may call the 'ambient' or surrounding stimulus.

p. 160 - The Scientific Analysis of Personality, 1965