Presentation Information
[P1-32]What’s the difference between a premature and a timed anticipatory movement ?
*Marcus Missal1, Dominika Drazyk1 (1. Université catholique de Louvain, Institute of Neuroscience (Belgium))
Keywords:
Temporal preparation,Eye movements,Anticipation,Impulsivity
Imagine yourself in a car race waiting for the traffic light to go green. Impulsivity could push you to accelerate prematurely when the light is red, causing a false start. In contrast, cognitively driven anticipation could lead you to accelerate right at the time the traffic light goes green and give you some advantage. Whether these two types of responses interact or are independent is an open question. Independent neural processes could be reflected in different characteristics like latency distribution, velocity and/or amplitude of the movement.The independence hypothesis was tested using an oculomotor task with a constant delay between a warning and an imperative visual stimuli. Delay duration was either 400, 900, 1400 or 1900 ms in blocks of 120 trials. Through repetition, subjects (n=27) implicitly learn the timing of the imperative stimulus. On average, 10% of experimental trials were associated with a response before the ‘go’ signal. The latency distribution of eye saccades during the delay before the ‘go’ signal was composed of two modes. With increasing delay duration, we found that: 1) The number of 1st mode saccadic responses decreased whereas the number of 2nd mode responses remained approximately constant; 2) The variance of 1st mode response latencies remained constant whereas the variance of 2nd mode responses increased; 3) The maximum velocity of 1st mode responses remained constant whereas it decreased for 2nd mode responses.These results show that collectively referring to movements before the ‘go’ stimulus as ‘anticipatory’ is inaccurate. There are probably two independent processes taking place before the ‘go’ stimulus: an unintentional release of inhibition evoking a premature saccade and an anticipatory process temporally guided. Premature saccades could be subcortically initiated whereas anticipatory saccades could be under the dependence of the cortical eye fields.