Berlyne had already suggested that curiosity also includes verbal activities, such as asking questions, and symbolic activities, consisting of internally fueled mental processes such as thinking ("epistemic exploration"). Theories Like other desires and need states that take on an appetitive quality (e.g. food), curiosity is linked with exploratory behavior and experiences of reward. Curiosity can be described as positive emotions and acquiring knowledge; when one's curiosity has been aroused it is considered inherently rewarding and pleasurable. Discovering new information may also be rewarding because it can help reduce undesirable states of uncertainty rather than stimulating interest. Theories have arisen in attempts to further understand this need to rectify states of uncertainty and the desire to participate in pleasurable experiences of exploratory behaviors. Curiosity-drive theory Curiosity-drive theory relates to the undesirable experiences of "uncertainty". The reduction of these unpleasant feelings, in turn, is rewarding. This theory suggests that people desire coherence and understanding in their thought processes. When this coherence is disrupted by something that is unfamiliar, uncertain, or ambiguous, it is curiosity-drive that attempts to gather information and knowledge of the unfamiliar to restore coherent thought processes. Through this theory, the general concept dictates that curiosity is developed strictly out of the desire to make sense of unfamiliar aspects of one's environment through interaction of exploratory behaviors. Once understanding of the unfamiliar has been achieved and coherence has been restored, these behaviors and desires will subside. Subsets of curiosity-drive theory differ on whether curiosity is a primary or secondary drive and if this curiosity-drive is originated due to one's need to make sense of and regulate their environment or if it is caused by an external stimulus. Causes can range from basic needs that need to be satisfied (e.g. hunger, thirst) to needs in fear induced situations. Each of these subset theories state that whether the need is primary or secondary curiosity is developed from experiences that create a sensation of uncertainty or perceived unpleasantness. Curiosity then acts as a means in which to dispel this uncertainty. By exhibiting curious and exploratory behavior, one is able to gain knowledge of the unfamiliar and thus reduce the state of uncertainty or unpleasantness. This theory, however, does not address the idea that curiosity can often be displayed even in the absence of new or unfamiliar situations. This type of exploratory behavior is common in many species. Take the example of a human