Dijksterhuis and Nordgren put forward a theory of unconscious thought. They propose that there are two types of thought process: conscious and unconscious. “CT (conscious thought) refers to object-relevant or task-relevant cognitive or affective thought processes that occur while the object or task is the focus of one’s conscious attention, whereas UT (unconscious thought) refers to object-relevant or task-relevant cognitive or affective thought processes that occur while conscious attention is directed elsewhere.’’
Like Kahneman’s System 1 and System 2 thought there is no implication here that there is purely conscious thought with no unconscious components but only that conscious awareness is part of the process. I prefer the System name as it avoids the possible interpretation that there might be purely conscious thought. System 1 is like UT and is characterized as: autonomous, fast, effortless, hidden/unconscious, simultaneous/parallel/complex. System 2 is like CT: deliberate, slow, effortful, conscious, serial/logical/simple. The most telling difference is whether working memory is used; working memory restricts the number of items that can be manipulated in thought to about 7 or less at a time and introduces the conscious awareness of the working memory. It is often viewed as a difference between calculation and estimation, or between explicit and implicit knowledge.
The way these two processes are compared is to set out a problem and then compare the results after one of three activities: the subjects can consciously think about the problem for a certain length of time; the subjects can spend the same amount of time doing something that completely engages their consciousness; or they can be giving no time at all and asked for the answer immediately after the problem is presented. It has been found that with complex problems with many ingredients, that System 1/UT gives more quality results then System 2/CT and both are better than immediate answers.
A recent paper by Li, Zhu and Yang looks at another comparison of the two ways of thinking. (citation below)
According to unconscious thought theory (UTT), unconscious thought is more adept at complex decision-making than is conscious thought. Related research has mainly focused on the complexity of decision-making tasks as determined by the amount of information provided. However, the complexity of the rules generating this information also influences decision making. Therefore, we examined whether unconscious thought facilitates the detection of rules during a complex decision-making task. Participants were presented with two types of letter strings. One type matched a grammatical rule, while the other did not. Participants were then divided into three groups according to whether they made decisions using conscious thought, unconscious thought, or immediate decision. The results demonstrated that the unconscious thought group was more accurate in identifying letter strings that conformed to the grammatical rule than were the conscious thought and immediate decision groups. Moreover, performance of the conscious thought and immediate decision groups was similar. We conclude that unconscious thought facilitates the detection of complex rules, which is consistent with UTT.
It is a characteristic of System 2/CT that it is used to rigorously follow rules to calculate a result. However there is a difference between following a rule and discovering one. This rule discovery activity may be the same as implicit learning. “Mealor and Dienes (2012) combined UT and implicit learning research paradigms to investigate the impact of UT on artificial grammar learning. A classic implicit learning paradigm consists of two stages: training and testing. ” The UT group had better results but they categorized the process as random selection. The current paper shows that the UT group can find the grammatical rules illustrated in the training and then identify grammatical as opposed to ungrammatical strings. System 1/UT is better at uncovering rules and of identifying examples that break the rules. This does not seem to be a rigorous following of rules as in System 2 but more a statistical tendency or a stereotypical categorization of the nature of implicit learning.
It is important to be clear that System 2 or CT is thought that has a conscious component and it does not imply that the thought is conducted ‘in’ consciousness. We are aware of the steps in a train of thought, but not aware of the process, they are hidden.
Li, J., Zhu, Y., & Yang, Y. (2014). The Merits of Unconscious Thought in Rule Detection PLoS ONE, 9 (8) DOI: 10.1371/journal.pone.0106557