Preparatory Processes In The Central Nervous Process

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Execution of voluntary acts is preceded by preparatory processes in the central nervous system (CNS). The task specifies the act required – a speech act, a manipulative act, a locomotor act – and preparatory processes specify when and how the act will be executed so that the task requirements are met in the prevailing conditions (Jeannerod 1994; Requin et al. 1991). Preparatory processes must therefore incorporate information about task requirements and environmental conditions in order to specify task-appropriate movement parameters that are passed to the neural machinery that generates motor commands to the muscles. The process of preparation is therefore often referred to as motor planning or motor programming (Kawato 1999; Keele et al. …show more content…
This phenomenon has been termed the StartReact effect (Valls-Solé et al. 1999). While most research on the StartReact involved simple RT tasks (for recent reviews see Marinovic and Tresilian 2016; Nonnekes et al. 2015), some studies have investigated the early release of motor actions by LAS using choice RT tasks. Kumru et al. (2006) showed that an LAS could trigger whatever motor response was prepared at the time of stimulation (e.g. correct or incorrect hand movement). Similarly, Forgaard et al. (2011) found participants released motor acts whose amplitude fell between targets when their movements were triggered by LAS. Thus, this relatively simple technique could provide a suitable readout concerning the state of motor preparation slightly prior to the voluntary decision to move. Given that no studies have investigated the impact of LAS on the directional accuracy of movement trajectories, in Experiment 1 we investigated how the presentation of the acoustic stimulus affects initial movement direction in simple and choice RT tasks. The results of experiment 1 suggest the acoustic stimulus does not affect the accuracy of the prepared movement in simple RT tasks. Moreover, the choice RT data suggest that as time to prepare progressively increases so does the accuracy of movement direction. In Experiment 2, we further examined how direction reprogramming develops by manipulating the probability of appearance of the targets, and the inter-stimulus-interval (ISI) between the imperative stimulus (IS, or visual target) and the LAS. Consistent with the proposal of multiple parallel motor programs, the results of experiment 2 showed that movement direction reprogramming occurs continuously but

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