We can cross temporal sensorimotor contin- gencies by remembering sensory events or by anticipat- ing motor responses. Here we tested the hypothesis that sensory and motor representations can be accessed ac- cording to different temporal dynamics. We predicted that the manipulation of movement representations would lead to a performance independent from the length of a delay interposed between sensory instructions and behavioural responses. Conversely, we expected a delay-dependent performance whenever temporary stor- age of sensory information was necessary to solve the task. We have measured reaction times and error rate in subjects performing a delayed non-matching to sample task. Task contingencies rather than explicit instructions ensured that either sensory or motor representations were used to cross the delay period on each trial. We tested our hypothesis by manipulating the length of the delays between stimulus presentation and behavioural response. We found that carrying sensory material over temporal gaps affects performance as a non-linear function of time, whereas movement representations remain robust over a wide range of delays. This novel behavioural par- adigm might prove effective in dissociating the neural bases of preparatory and mnestic processes in normal hu- man subjects, as well as their disorders in neurological patients.
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