Flexible viewing time when estimating time-to-contact in 3D parabolic trajectories

Prediction of time to contact under perceptual and contextual uncertainties

Accurately estimating time to contact (TTC) is crucial for successful interactions with moving objects, yet it is challenging under conditions of sensory and contextual uncertainty, such as occlusion. In this study, participants engaged in a prediction motion task, monitoring a target that moved rightward and an occluder. The participants' task was to press a key when they predicted the target would be aligned with the occluder's right edge. We manipulated sensory uncertainty by varying the visible and occluded periods of the target, thereby modulating the time available to integrate sensory information and the duration over which motion must be extrapolated. Additionally, contextual uncertainty was manipulated by having a predictable and unpredictable condition, meaning the occluder either reliably indicated where the moving target would disappear or provided no such indication. Results showed differences in accuracy between the predictable and unpredictable occluder conditions, with different eye movement patterns in each case. Importantly, the ratio of the time the target was visible, which allows for the integration of sensory information, to the occlusion time, which determines perceptual uncertainty, was a key factor in determining performance. This ratio is central to our proposed model, which provides a robust framework for understanding and predicting human performance in dynamic environments with varying degrees of uncertainty.

Virtual reality modulates the control of upper limb motion in one-handed ball catching

There remains a question about whether and to what extent perception-action coupled response in virtual reality are equal/unequal to those in the real world or physical reality. The purpose of this study was to identify the differences in the environmental effect of virtual presentation on the motor responses of a one-handed ball catching. Thirteen healthy participants were instructed to catch an approaching ball projected at three speeds in a real laboratory room and in a room-sized virtual reality system (CAVE) that simulated those real situations with two- or three-dimensional display settings. The results showed that the arm movement time, which denotes the duration of arm-raising motion (shoulder flexion), was significantly longer in the virtual reality than that in the physical reality at the fast ball speed condition. The shoulder flexion velocities, calculated as the average angular velocity of shoulder flexion over the arm movement time, were significantly lower in the virtual reality than in the physical reality at the medium and fast ball speed conditions. The electromyography onsets, derived from anterior deltoid, biceps brachii, and flexor carpi radialis muscles of the catching arm, appeared before and significantly closer to the initiation of arm raising in the two-dimensional virtual reality than both in the physical reality and in the three-dimensional virtual reality. The findings suggest that simulation of virtual reality may induce a modulation in the motor responses of the catching arm, which is different from natural motion that appeared in the real world. On the contrary, the effect of ball speed generally found in real setting was maintained in the current CAVE experiment.

Motion-in-depth effects on interceptive timing errors in an immersive environment

We often need to interact with targets that move along arbitrary trajectories in the 3D scene. In these situations, information of parameters like speed, time-to-contact, or motion direction is required to solve a broad class of timing tasks (e.g., shooting, or interception). There is a large body of literature addressing how we estimate different parameters when objects move both in the fronto-parallel plane and in depth. However, we do not know to which extent the timing of interceptive actions is affected when motion-in-depth (MID) is involved. Unlike previous studies that have looked at the timing of interceptive actions using constant distances and fronto-parallel motion, we here use immersive virtual reality to look at how differences in the above-mentioned variables influence timing errors in a shooting task performed in a 3D environment. Participants had to shoot at targets that moved following different angles of approach with respect to the observer when those reached designated shooting locations. We recorded the shooting time, the temporal and spatial errors and the head's position and orientation in two conditions that differed in the interval between the shot and the interception of the target's path. Results show a consistent change in the temporal error across approaching angles: the larger the angle, the earlier the error. Interestingly, we also found different error patterns within a given angle that depended on whether participants tracked the whole target's trajectory or only its end-point. These differences had larger impact when the target moved in depth and are consistent with underestimating motion-in-depth in the periphery. We conclude that the strategy participants use to track the target's trajectory interacts with MID and affects timing performance.

Gravity and Known Size Calibrate Visual Information to Time Parabolic Trajectories

Catching a ball in a parabolic flight is a complex task in which the time and area of interception are strongly coupled, making interception possible for a short period. Although this makes the estimation of time-to-contact (TTC) from visual information in parabolic trajectories very useful, previous attempts to explain our precision in interceptive tasks circumvent the need to estimate TTC to guide our action. Obtaining TTC from optical variables alone in parabolic trajectories would imply very complex transformations from 2D retinal images to a 3D layout. We propose based on previous work and show by using simulations that exploiting prior distributions of gravity and known physical size makes these transformations much simpler, enabling predictive capacities from minimal early visual information. Optical information is inherently ambiguous, and therefore, it is necessary to explain how these prior distributions generate predictions. Here is where the role of prior information comes into play: it could help to interpret and calibrate visual information to yield meaningful predictions of the remaining TTC. The objective of this work is: (1) to describe the primary sources of information available to the observer in parabolic trajectories; (2) unveil how prior information can be used to disambiguate the sources of visual information within a Bayesian encoding-decoding framework; (3) show that such predictions might be robust against complex dynamic environments; and (4) indicate future lines of research to scrutinize the role of prior knowledge calibrating visual information and prediction for action control.