Abstract
The default mode of the motor system is a coupling between limbs. However, in some movements, a decoupling is required and thus calls for selection and facilitation/inhibition processes. Here, we investigate the relative contribution of recruitment versus selection processes to the overall processing complexity. To this aim we proposed a new multilimb reaction-time task (MUL-RT). Simple, choice and normalized (choice minus simple) RT were analysed together with error rates in thirty-six young adults for 15 coordination modes including all possible configuration of limb recruitment. Simple and normalized RTs were respectively assumed to be indicative of the recruitment and selection processes. Results supported a model of coupling/decoupling interactions respectively reporting weak, intermediate and strong interaction for selecting diagonal, ipsilateral and homologous limbs. Movement laterality (left vs. right) had no effect on selection complexity, whereas selecting upper limbs was less challenging than selecting lower limbs. Results in the different coordination modes suggested that recruitment complexity decreased as follows: 3 limbs = 4 limbs>2 limbs (homologous, ipsilateral and diagonal)>1 limb, and selection complexity as follows: 2 diagonal limbs>3 limbs>2 ipsilateral limbs>1 limb = 2 homologous limbs>4 limbs. Based on these ordinal scales of recruitment and selection complexity, we extrapolated the overall processing complexity of the simple and choice MUL-RT. This method was efficient in reproducing the absolute results we obtained on a ratio scale (ms) and demonstrated that processing complexity in simple RT was mainly governed by the ‘recruitment principle’ (the more limbs recruited the lower the performance), whereas contributions of recruitment and ‘selection principle’ (nature of the coordination determines performance) to overall processing complexity were similar in choice RT.
Highlights
Reaction time (RT) refers to the time elapsing between a stimulus and a detectable movement, a physical change, or an action, occasioned by the occurrence of the stimulus [1]
Simple RT tasks require the participant to respond to the presence of a single stimulus
Simple RT is shorter than a recognition RT, and choice RT is longest of all [4]
Summary
Reaction time (RT) refers to the time elapsing between a stimulus and a detectable movement, a physical change, or an action, occasioned by the occurrence of the stimulus [1]. RT is considered to be an index of speed and efficiency of central processing afforded by the brain [3]. Simple RT tasks require the participant to respond to the presence of a single stimulus. Recognition RT tasks require the participant to respond when one specific stimulus appears and to withhold his response when other types of stimuli are presented. Choice RT tasks require distinct responses for each type of stimulus. Simple RT is shorter than a recognition RT, and choice RT is longest of all [4]. Longer RT is assumed to be indicative of more complex processing requirements and/or the degree of integrity of the central nervous system. Few studies have addressed whether the particular combination of limbs affects task performance
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