Implicit Coding of the Temporal Structure of Events

Abstract

We explore the implicit mechanisms of temporal coding by examining how events are processed within temporal windows of 30ms. Events within temporal windows are judged as simultaneous, but this is based on experiments in which subjects are explicitly instructed to decide whether two stimuli are simultaneous or not. Our previous studies already suggested that asynchronous stimuli judged to be simultaneous are nonetheless distinguished in time (Lalanne, Van Assche, & Giersch, 2012). In the present work, we wanted to study these implicit abilities as directly as possible. To do so, we built new tests, which aims were to verify the hypothesis that successive events that occur within ‘elementary time windows’ are in fact distinguished in time and to probe whether or not subjects are able to follow events over time and code an order.Our first paradigm was aimed at testing whether or not there is an implicit coding of order when two visual stimuli (primers) are presented in close succession. These primers were square frames displayed on the right and left side of the screen with an asynchrony of 17ms. The order of the primers was thus either left-right or right-left. After a 100ms delay, the frames were filled in, and the right-left or left right order of this filling-in represented the target information. Subjects had to decide on which side the last filling-in had occurred. It is only if primers are distinguished in time that reaction times (RTs) can be expected to vary according to the order of primers. We wanted to know whether the primers are automatically ordered or not, resulting, or not, in faster RTs when primers and targets are presented in the same order.Our second paradigm was aimed at checking whether an implicit effect and a bias to the side of the second primer can be observed in a task that does not require a temporal judgment. Experiment 2 was the same as Exp. 1 except that subjects had to detect a single target displayed to the side of one of the two primers.In Exp. 1, RTs varied with the order of the primers. RTs were faster if the last filled-in target was to the side of the first primer. These results are exactly the reverse of what was expected in case of order (or direction) coding. These results confirm that the asynchrony is coded implicitly but this is not the case for order. The results can be explained by an automatic bias towards the second primer, which might facilitate the coding of the targets order by priming the first target, like in the prior entry effect (Spence & Parise, 2010).In Exp. 2, primers’ order again influenced responses, and this influence evolved with time. At a 25ms delay after the primers presentation, subjects were faster when the target appeared to the side of the first prime. In contrast, at a 100ms delay, subjects were slower. In all these experiments, we checked that subjects did not detect the primers’ asynchrony. Our data confirm that events are distinguished in time at an implicit level. The results suggest that subjects’ focus is on the first primer immediately after the primers presentation, and then moves away from this location. There was no evidence, however, that attention automatically moved towards the second primer in Experiment 2, when there was no temporal judgment involved. It was only in Exp. 1, when a temporal judgment was involved, that there was evidence of an automatic focus towards the second primer. All in all the results show an implicit processing of events in time within the temporal windows. However, moving attention from one event to another requires a task incentive, suggesting tight interactions between automatic time event structure processing and task-related expectancies.