Temporal estimation with two moving objects: overt and covert pursuit

The current study examined temporal estimation in a prediction motion task where participants were cued to overtly pursue one of two moving objects, which could either arrive first, i.e., shortest [time to contact (TTC)] or second (i.e., longest TTC) after a period of occlusion. Participants were instructed to estimate TTC of the first-arriving object only, thus making it necessary to overtly pursue the cued object while at the same time covertly pursuing the other (non-cued) object. A control (baseline) condition was also included in which participants had to estimate TTC of a single, overtly pursued object. Results showed that participants were able to estimate the arrival order of the two objects with very high accuracy irrespective of whether they had overtly or covertly pursued the first-arriving object. However, compared to the single-object baseline, participants’ temporal estimation of the covert object was impaired when it arrived 500 ms before the overtly pursued object. In terms of eye movements, participants exhibited significantly more switches in gaze location during occlusion from the cued to the non-cued object but only when the latter arrived first. Still, comparison of trials with and without a switch in gaze location when the non-cued object arrived first indicated no advantage for temporal estimation. Taken together, our results indicate that overt pursuit is sufficient but not necessary for accurate temporal estimation. Covert pursuit can enable representation of a moving object’s trajectory and thereby accurate temporal estimation providing the object moves close to the overt attentional focus

Influence de la gravité sur la perception et l'interrception d'objets en mouvement

In order to explain Humans' success in interceptive actions of gravitationally accelerated objects, despites the low capacity of the visual system to detect it, several studies have recently suggested that gravity has been embodied in a quantitative internal model of gravity thereby permitting access to exact time-to-contact (TTC) when intercepting a free falling object. However, we may wonder if theoretical and methodological concerns in these experiments cannot call into question the effective demonstration of the existence and use of such a model. The goal of this doctoral work was to determine how our knowledge of gravity influences our perception and actions. We conducted six experimentations issued from three different paradigms, perceptive judgement, indirect interception and direct interception. Our results refute the use of a quantitative internal model of gravity, and plead in favour of the use of our knowledge of gravity as a qualitative implicit physics knowledge, which would modulate our perceptive judgements and interceptive movements but without giving access to the quantitative effects of gravity.Pour expliquer le succès des individus dans des tâches d'interception d'objets accélérés par la gravité malgré sa faible détection par le système visuel, plusieurs études ont récemment suggéré que la gravité soit internalisée dans un modèle interne de la gravité permettant l'accès au temps de contact (TTC) exact lors de l'interception d'objets en chute libre. Cependant, on peut se demander si certains problèmes méthodologiques et théoriques ne peuvent pas remettre en cause la démonstration de l'existence et l'utilisation effective d'un tel modèle. Le but de ce travail doctoral a été de déterminer de quelle manière notre connaissance de la gravité influence notre perception et nos actions. Pour cela, nous avons conduit six expérimentations issues de trois paradigmes différents, celui des jugements perceptifs, des actions d'interception indirectes et des actions d'interception directes. Les résultats obtenus infirment l'utilisation d'un modèle interne quantitatif de la gravité, et au contraire suggèrent l'utilisation de la gravité comme une connaissance implicite qualitative de la physique, qui aurait pour conséquence de modifier nos jugements perceptifs et nos mouvements d'interception sans permettre de calculer quantitativement les effets de la gravité

Asymmetrical time-to-contact error with two moving objects persists across different vertical separations

Copyright © 2018 Elsevier B.V. All rights reserved.When human observers estimate the time-to-contact (TTC) of more than one object there is an asymmetric pattern of error consistent with prioritizing the lead object at the expense of the trail object. Here, we examined TTC estimation in a prediction motion task where two objects moved along horizontal trajectories (5 or 7.5 °/s) that had different vertical separation, and thus placed specific demands on visuospatial attention. Results showed that participants were able to accurately judge arrival order, irrespective of vertical separation, in all but two conditions where the object trajectories crossed close to the arrival location. Constant error was significantly higher for the object that trailed, as opposed to led, by 250 or 500 ms. Asymmetry in constant error between the lead and trail object was not influenced by vertical separation, and was also evident across a range of arrival times. However, while the lag between the two consecutive TTC estimations was scaled to the actual difference in object arrival times, lag did increase with vertical separation. Taken together, our results confirm that TTC estimation of two moving objects in the prediction motion task suffers from an asymmetrical interference, which is likely related to factors that influence attentional allocation.PostprintPeer reviewe

Crossing a Multi-Lane Street: Irrelevant Cars Increase Unsafe Behavior

Before crossing a road or an intersection, road users have to determine among the surrounding traffic whether or not they have enough time to safely complete their maneuver. Temporal judgments have been investigated for single cars approaching an intersection, however, close to nothing is known about how street-crossing decisions are being made when several vehicles are simultaneously approaching in two adjacent lanes. We conducted a simulator experiment in which observers indicated whether or not they had enough time to complete safe street crossing. Traffic gaps were presented either with a single or two oncoming cars on different lanes, in such a way that in all cases, only the shortest gap was taskrelevant. Nevertheless, street-crossing decisions were found to be also influenced by the task-irrelevant longer gap, observers being more willing to cross the street when having to judge two gaps simultaneously compared to only one gap. Consequences of this unsafe behavior are discussed

Visual discrimination thresholds for time to arrival

810, 1981) reported a difference threshold of about 50 ms to discriminate the times of arrival of two differently sized objects that simultaneously approached head-on at constant but different velocities. Subsequent investigators, however, have often found much higher thresholds. We did one com-plete replication of Todd’s experiment, and then modified his stimuli and experimental regime, which we hypothesized may have been responsible for some of the discrepancies reported in the literature. Unlike Todd and most other re-searchers, we exclusively used untrained observers. Several of our participants performed almost as well as the trained observers used by Todd and others, but the performance of most of our participants fell short of this standard. Further-more, thresholds were affected by the experimental regimes, with large differences between objects ’ sizes and speeds compromising performance. Analyses of the response pat-terns revealed that the responses were driven mainly by the objects ’ relative apparent sizes

The detrimental influence of attention on time-to-contact perception

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