Emotions are a near-universal component of human experience, with powerful influences on human attitudes and behaviors, and large-scale social, economic, and environmental consequences (Zajonc, 1984; Oatley et al., 2006; Turner and Stets, 2006; Nesse and Ellsworth, 2009; Niedenthal and Brauer, 2012; Dehaene, 2014). They have been described as a continuum that includes over 100 named emotions, with some individual and cultural differences (Johnson-Laird and Oatley, 1989; Nesse and Ellsworth, 2009; Izard, 2010). These are sometimes treated as combinations of basic emotions (Ortony and Turner, 1990), recognizable through facial expressions (Ekman, 1982; Dannlowski et al., 2007; Graham and LaBar, 2012). The neurophysiological and biochemical mechanisms and effects of human emotions have been analyzed intensively (LeDoux, 2000; Ackerl et al., 2002; Chen et al., 2006; Mujica-Parodi et al., 2009; Zhou and Chen, 2009; Haegler et al., 2010; Van Westerloo et al., 2011; Agren et al., 2012; Gross and Canteras, 2012; Avila and Lin, 2014; Dehaene, 2014). All such measures, however, rely on research subjects also communicating their self-perceived emotions to the researcher. Similarly, for analyses of psychological experiences rather than biochemical or neurological mechanisms, research subjects must express their emotional experiences in words and communicate them to researchers. The latter also use language to communicate their analyses to research readers. They may include selected quotations directly from the research subjects. Comprehension of such communications about emotions depends on mutual recognition of similar emotional experiences.

This approach breaks down, however, for emotions that are not widely experienced, and which are considered to be indescribable by those who have indeed experienced them. The popular literatures of ecstatic religions, active military combat, and extreme outdoor sports all argue that there are feelings that are only comprehensible to individuals who have experienced them in person (Caputo, 1977; Allman et al., 2009; Buckley, 2012; Yogis, 2013). These experiences include the perception of slowed time (Arstila, 2012; Wittmann, 2013; Buckley, 2014). Human societies thus include a small number of individuals who have experienced emotions of a type or intensity that fall outside the distributional range for the remainder of the population. These differences are recognized by the rest of society, which may label those individuals as eccentric, sick or crazy, with either positive or negative connotations. For at least some individuals, these emotional experiences drive them to take actions that are considered unusual or extreme, also in either a negative or positive way. There are extensive literatures on the psychologies of crime, combat, mental illness, spirituality and extreme sport, reflecting the importance of these emotions and actions to human societies (Lyng, 1990; Buckley, 2012).