Table 1.

Examples of paradigms used to measure habit-related constructs in humans.

Paradigm	Source/first use	Short description of the paradigm	Selection of studies in humans using this paradigm
Probabilistic classification task, e.g., “Weather prediction task”	Gluck and Bower (31)	Subjects gradually learn to classify stimuli into two categories, based on trial-by-trial feedback. Because of the probabilistic structure of the task, the normal tendency to try to memorize a solution is defeated, and therefore subjects can learn without the use of declarative memory. Since the most useful information is acquired across many trials, the task is proposed to involve gradually acquired habit learning	Knowlton et al. (32), Knowlton et al. (33), Foerde et al. (34)
Discrimination learning task	Bayley et al. (35)	A declarative memory task where habit memory is proposed to involve slowly acquired associations between stimuli and responses that develop outside awareness and are rigidly organized, with the result that what is learned is not readily expressed except when the task is presented just as it was during training	n.a.#
Instrumental conditioning task	Valentin et al. (36)	Overtraining on a probabilistic instrumental learning task (choosing between drinks), followed by devaluation (selective satiation on one drink)	Schwabe and Wolf (37), Schwabe et al. (38), Hogarth et al. (39)
Free operant task	Tricomi et al. (40)	Subjects are either given little training, or are over trained on instrumental responding, with a rewarding outcome delivered on a variable-interval reinforcement schedule. This is followed by outcome devaluation and an extinction test	n.a.#
Instrumental learning task “Fabulous fruit game”	De Wit et al. (41)	Instrumental learning based on either stimulus–response-outcome (goal-directed) contingencies or direct stimulus–response (habitual) learning induced by conflict. Followed by an instructed outcome devaluation test, and a “slips of action” test, measuring habitual tendencies	Gillan et al. (42)*, De Wit et al. (43), Sjoerds et al. (21)**
Markov decision task	Daw et al. (44)	Applied in the computational neuroscience framework, based on the reinforcement learning theory. A forced choice task that can be solved by using either model-free (inflexible, computationally efficient, habit-like), or model-based (forward planning, flexible, goal-directed-like) control	Gläscher et al. (45), Wunderlich et al. (46), Smittenaar et al. (47)
Shock avoidance learning	Gillan et al. (48)*	Inducing habits by overtraining on avoiding electric shocks, followed by an instructed outcome devaluation phase to test for the level of habit formation	n.a.#

We do not aim to provide a comprehensive overview of methods for habit measurement. For a more complete overview of frequently used paradigms in the current habit literature, we refer the reader to the recent review by Dolan and Dayan (27).

^#To the best of our knowledge there have not been other studies using this paradigm to measure habit-related constructs.

*Applied in an obsessive–compulsive disorder (OCD) population.

**Applied in an addiction population (alcohol dependence patients).