The Mechanisms of Space-Time Association: Comparing Motor and Perceptual Contributions in Time Estimation.

Time and space are deeply related in the physical word. Growing experimental evidence suggests that temporal events are represented on a mental time line (MTL), spatially oriented from left to right. According to task characteristics, the spatial representation of time can be linked to different types of dimensions including manual response codes (i.e the Spatial-Temporal Association of Response Codes - STEARC) and physical space codes (i.e. the position of a stimulus in the physical space). It is unclear whether this spatial-temporal association is mainly related to a perceptual, to a motor or to an interaction of these two components. The aim of the present a study was to analyze whether manual response and physical space codes are independent from each other or they interacted when both types of information are involved in a temporal estimation task. Through four experiments, participants were requested to perform the task with two lateralized response buttons, in order to detect the STEARC effect. In addition, in order to consider the perceptual component, reference and target stimuli were presented in different spaces through the experiments. In the first experiment, the target stimuli were presented on the left, center or right side of the space, while the reference stimuli were always presented centrally. The reverse situation was presented in the second experiment. In the third experiment, both stimuli were presented in opposite spatial positions (e.g., left-right), while in the last experiment, both stimuli were presented in the same spatial position (e.g., left-left). In Experiments 1-1, the performance was better when both manual response and physical space codes were congruent with the durations to be judged than when only manual response codes were congruent (and physical space codes were either incongruent or absent) with the durations. In Experiment 4, this interactive effect between both codes disappeared. The results indicate that the physical spatial codes interact with the manual response codes when the task characteristics involved spatial information of both perceptual and motor components, suggesting that they are not completely independent from each other.