title: Implicit and explicit timing in oculomotor control.
abstract: The passage of time can be estimated either explicitly, e.g. before leaving home in the morning, or implicitly, e.g. when catching a flying ball. In the present study, the latency of saccadic eye movements was used to evaluate differences between implicit and explicit timing. Humans were required to make a saccade between a central and a peripheral position on a computer screen. The delay between the extinction of a central target and the appearance of an eccentric target was the independent variable that could take one out of four different values (400, 900, 1400 or 1900 ms). In target trials, the delay period lasted for one of the four durations randomly. At the end of the delay, a saccade was initiated by the appearance of an eccentric target. Cue&target trials were similar to target trials but the duration of the delay was visually cued. In probe trials, the duration of the upcoming delay was cued, but there was no eccentric target and subjects had to internally generate a saccade at the estimated end of the delay. In target and cue&target trials, the mean and variance of latency distributions decreased as delay duration increased. In cue&target trials latencies were shorter. In probe trials, the variance increased with increasing delay duration and scalar variability was observed. The major differences in saccadic latency distributions were observed between visually-guided (target and cue&target trials) and internally-generated saccades (probe trials). In target and cue&target trials the timing of the response was implicit. In probe trials, the timing of the response was internally-generated and explicitly based on the duration of the visual cue. Scalar timing was observed only during probe trials. This study supports the hypothesis that there is no ubiquitous timing system in the brain but independent timing processes active depending on task demands.
authors.affiliation: Institute of Neurosciences (IONS), Cognition and System (COSY), Université catholique de Louvain, Brussels, Belgium.
authors.forename: Ilhame
authors.initials: I
authors.lastname: Ameqrane
authors.affiliation: Institut du Cerveau et de la Moëlle (ICM), CNRS UMR 7225, Paris, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Pouget
authors.affiliation: Institut du Cerveau et de la Moëlle (ICM), CNRS UMR 7225, Paris, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Wattiez
authors.affiliation: Department of Physiology, Development and Neuroscience (PDN), Cambridge University, Cambridge, United Kingdom.
authors.forename: Roger
authors.initials: R
authors.lastname: Carpenter
authors.affiliation: Institute of Neurosciences (IONS), Cognition and System (COSY), Université catholique de Louvain, Brussels, Belgium.
authors.forename: Marcus
authors.initials: M
authors.lastname: Missal
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009801:Oculomotor Muscles / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012438:Saccades / Q000502:physiology
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