:Loewenstein<ref>[http://www.andrew.cmu.edu/user/gl20/GeorgeLoewenstein/Papers_files/pdf/PsychofCuriosity.pdf Loewenstein, George. "The psychology of curiosity: A review and reinterpretation." Psychological bulletin 116.1 (1994): 75.‏]</ref> suggests that when individuals encounter novel, complex, or ambiguous stimuli, they may find there are discrepancies between information that is known and unknown—indicative of a “knowledge gap”.The perceived magnitude of such gaps are based on feeling-of-knowing (FOK) judgements, which are metacognitive estimates of one’s available (i.e.,retrievable) knowledge (Brown & McNeil], 1966; Eysenck, 1979; I-Iart, 1965).According to Loewenstein (1994), stronger FOI(s correspond with smaller perceived knowledge gaps, and result in feeling closer to figuring or finding out the desired knowledge (Loewenstein, 1994; Loewenstein, Adler, Behrens, & Gillis, I992). Based on Miller’s (1959) approach-gradient theory, which predicts that the intensity of motives increase as one approaches goal achievement,Loewenstein (I994) hypothesises that as FOI(s become stronger, knowledge gaps will seem smaller, and states of curiosity will intensify as individuals perceive themselves close to eliminating their knowledge discrepancy and the associated feelings of tension. In one study, Loewenstein et al. (1992) asked."<ref>Litman, Jordan. "Curiosity and the pleasures of learning: Wanting and liking new information." Cognition & emotion 19.6 (2005): 793-814.‏</ref>

===Optimal stimulation/two process/plesure of expolration vs. anxiety===