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Scientific understanding of how the mind generates bodily actions remains opaque. In the early 19th century, the ideomotor theory proposed that humans generate voluntary actions by imagining the sensory consequence of those actions, implying that the idea of an action's consequence mediates between the intention to act and motor control. Despite its long history and theoretical importance, existing empirical evidence for the ideomotor theory is not strong enough to rule out alternative hypotheses. In this study, we devised a categorization-action task to evaluate ideomotor theory by testing whether an idea, distinguished from a stimulus, can modulate task-irrelevant movements. In Experiment 1, participants categorized a stimulus duration as long or short by pressing an assigned key. The results show that participants pressed the key longer when categorizing the stimulus as long than they did when characterizing it as short. In Experiment 2, we showed that the keypressing durations were not modulated by the decision category when the property of the decision category, the brightness of a stimulus, was not easily transferable to the action. In summary, our results suggest that while the perceived stimulus features have a marginal effect on response duration linearly, the decision category is the main factor affecting the response duration. Our results indicate that an abstract category attribute can strongly modulate action execution, constraining theoretical conjectures about the ideomotor account of how people voluntarily generate action.

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Many decisions in life are sequential and constrained by a time window. Although mathematically derived optimal solutions exist, it has been reported that humans often deviate from making optimal choices. Here, we used a secretary problem, a classic example of finite sequential decision-making, and investigated the mechanisms underlying individuals' suboptimal choices. Across three independent experiments, we found that a dynamic programming model comprising subjective value function explains individuals' deviations from optimality and predicts the choice behaviors under fewer and more opportunities. We further identified that pupil dilation reflected the levels of decision difficulty and subsequent choices to accept or reject the stimulus at each opportunity. The value sensitivity, a model-based estimate that characterizes each individual's subjective valuation, correlated with the extent to which individuals' physiological responses tracked stimuli information. Our results provide model-based and physiological evidence for subjective valuation in finite sequential decision-making, rediscovering human suboptimality in subjectively optimal decision-making processes.

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Task parameters still affect reaction times even when all necessary information for executing an action is presented prior to a Go signal to execute the action. Hypotheses in terms of short-term memory capacity, residual activation, and a separate motor-programming stage have been suggested to explain what can and cannot be prepared prior to a delayed Go signal. To test these hypotheses, we used a delayed response task, in which participants were to initiate a movement at onset of an imperative Go signal following the target stimulus. Across Experiments 1-3 we varied task properties including stimulus type, information uncertainty and response complexity, respectively, while controlling other factors. We also varied the time available to process the response by randomly varying the interval between onset of the target and the Go signal (i.e., the stimulus onset asynchrony, or SOA). If the preparation process is completed before initiation, the examined factor should display a strong interaction with SOA, with its effect disappearing at long SOAs. Our results showed strong, weaker, and no interaction patterns for the three factors, respectively, favoring the separate stage hypothesis, according to which response preparation is separated into steps to arrange kinematic specifications into muscle-controllable terms.

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Ideomotor theory accounts for how an action's consequence is incorporated into an action concept in the form of a perceptual image that, when retrieved, serves to initiate the action. The ideomotor idea is compelling, because the ultimate purpose of an action is to bring about a certain change in the environment. This study investigated the time-course of response-effect compatibility (REC), which produces a shorter reaction-time when response effects are compatible with the responses than when they are not. We used a delayed choice-reaction task that required the response to be withheld until a Go signal occurred. In Experiment 1 an effect was delivered by the location of a square in either a spatially compatible or incompatible relation to the keypress action. A significant REC effect for reaction time was found only when an effect-achieving instruction was used, for which evidence indicated a locus in an early action phase. In Experiment 2 a cursor effect occurred causally, continuously and simultaneously with the movement of a computer mouse. No matter whether instructions in terms of cursor or mouse movement were used, a strong REC effect was found that preserved its power from the early to later parts of motor planning until execution ended. The results provide evidence that an action concept incorporates the action's consequent changes more strongly when they are goal-satisfying or highly causal events.

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A framework for action planning, called ideomotor theory, suggests that actions are represented by their perceivable effects. Thus, any activation of the effect image, either endogenously or exogenously, will trigger the corresponding action. We review contemporary studies relating to ideomotor theory in which researchers have investigated various manipulations of action effects and how those effects acquire discriminative control over the actions. Evidence indicates that the knowledge about the relation between response and effect is still a critical component even when other factors, such as stimulus-response or response-response relations, are controlled. When consistent tone effects are provided after responses are made, performance in serial-reaction tasks is better than when the effects are random. Methodology in which acquisition and test stages are used with choice-reaction tasks shows that an action is automatically associated with its effect bilaterally and that anticipation of the effect facilitates action. Ideomotor phenomena include stimulus-response compatibility, in which the perceptual feature of the stimulus activates its corresponding action code when the stimulus itself resembles the effect codes. For this reason, other stimulus-driven action facilitation such as ideomotor action and imitation are treated as ideomotor phenomena and are reviewed. Ideomotor theory also implies that ongoing action affects perception of concurrent events, a topic which we review briefly. Issues concerning ideomotor theory are identified and evaluated. We categorize the range of ideomotor explanations into several groups by whether intermediate steps are assumed to complete sensorimotor transformation or not and by whether a general theoretical framework or a more restricted one is provided by the account.

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Previous studies have paired a visual-manual Task 1 with an auditory-vocal Task 2 to evaluate whether the psychological refractory period (PRP) effect is eliminated with two ideomotor-compatible tasks (for which stimuli resemble the response feedback). The present study varied the number of stimulus-response alternatives for Task 1 in three experiments to determine whether set-size and PRP effects were absent, as would be expected if the tasks bypass limited-capacity response-selection processes. In Experiments 1 and 2, the visual-manual task was used as Task 1, with lever-movement and keypress responses, respectively. In Experiment 3, the auditory-vocal task was used as Task 1 and the visual-manual task as Task 2. A significant lengthening of reaction time for 4 vs. 2 alternatives was found for the visual-manual Task 1 and the Task 2 PRP effect in Experiments 1 and 2, suggesting that the visual-manual task is not ideomotor compatible. Neither effect of set size was significant for the auditory-vocal Task 1 in Experiment 3, but there was still a Task 2 PRP effect. Our results imply that neither version of the visual-manual task is ideomotor compatible; other considerations suggest that the auditory-vocal task may also still require response selection.

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It has been argued that the psychological refractory period (PRP) effect is eliminated with two ideomotor compatible tasks when instructions stress fast and simultaneous responding. Three experiments were conducted to test this hypothesis. In all experiments, Task 1 required spatially compatible manual responses (left or right) to the direction of an arrow, and Task 2 required saying the name of the auditory letter A or B. In Experiments 1 and 3, the manual responses were keypresses made with the left and right hands, whereas in Experiment 2 they were left-right toggle-switch movements made with the dominant hand. Instructions that stressed response speed reduced reaction time and increased error rate compared to standard instructions to respond fast and accurately, but did not eliminate the PRP effect on Task 2 reaction time. These results imply that, even when response speed is emphasized, ideomotor compatible tasks do not bypass response selection.

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