In relation to perception, a type of non-conscious affect may be separate from the cognitive processing of environmental stimuli. A monohierarchy of perception, affect and cognition considers the roles of arousal, attention tendencies, affective primacy (Zajonc, 1980), evolutionary constraints (Shepard, 1984; 1994), and covert perception (Weiskrantz, 1997) within the sensing and processing of preferences and discriminations. Emotions are complex chains of events triggered by certain stimuli. There is no way to completely describe an emotion by knowing only some of its components. Verbal reports of feelings are often inaccurate because people may not know exactly what they feel, or they may feel several different emotions at the same time. There are also situations that arise in which individuals attempt to hide their feelings, and there are some who believe that public and private events seldom coincide exactly, and that words for feelings are generally more ambiguous than are words for objects or events. Therefore, non-conscious emotions need to be measured by measures circumventing self-report such as the Implicit Positive and Negative Affect Test (IPANAT; Quirin, Kazén, & Kuhl, 2009).