Visual Time Delay Research Articles

Modeling Human Control of Self-Motion Direction With Optic Flow and Vestibular Motion

In this paper, we investigate the effects of visual and motion stimuli on the manual control of one's direction of self-motion. In a flight simulator, subjects conducted an active target-following disturbance-rejection task, using a compensatory display. Simulating a vehicular control task, the direction of vehicular motion was shown on the outside visual display in two ways: an explicit presentation using a symbol and an implicit presentation, namely, through the focus of radial outflow that emerges from optic flow. In addition, the effects of the relative strength of congruent vestibular motion cues were investigated. The dynamic properties of human visual and vestibular motion perception paths were modeled using a control-theoretical approach. As expected, improved tracking performance was found for the configurations that explicitly showed the direction of self-motion. The human visual time delay increased with approximately 150 ms for the optic flow conditions, relative to explicit presentations. Vestibular motion, providing higher order information on the direction of self-motion, allowed subjects to partially compensate for this visual perception delay, improving performance. Parameter estimates of the operator control model show that, with vestibular motion, the visual feedback becomes stronger, indicating that operators are more confident to act on optic flow information when congruent vestibular motion cues are present.

Multimodal Pilot Control Behavior in Combined Target-Following Disturbance-Rejection Tasks

Investigating how humans use their perceptual modalities while controlling a vehicle is important for the design of new control systems and the optimization of simulator motion cueing. For the identification of separate pilot response functions to the different perceived cues, multiple forcing functions need to be inserted into the manual control loop. An example of a task with multiple forcing functions is a combined target-following disturbance-rejection task, where a target and disturbance signal are used to separate the human visual and vestibular motion responses. The use of multiple forcing functions, however, also affects the nature of the control task and how the motion cues are used by the pilot to form a proper control action. This paper presents the results of an experiment where possible effects of using multiple forcing functions on pilot control behavior in an aircraft pitch control task are investigated. The results indicate that pilot performance and control activity are significantly lower when the relative power of the target forcing function is increased. This is caused by a significant change in multimodal pilot control behavior. With an increase in relative target power, the visual-perception gain is reduced and the visual time delay becomes higher. The motion-perception gain reduces if both forcing functions have significant power. It is also found that multimodal pilot control behavior in a pure target or disturbance task can be analyzed by adding a small additional disturbance or target signal, respectively. In this case, the effects on control behavior are found to be minimal, while still being able to accurately estimate the parameters of the multichannel pilot model.

The effect of delayed visual feedback on telerobotic surgery

Telerobotic surgery is ideally suited for remote applications in which the instrument control console is stationed separately from the end-effectors at the patient's bedside. However, if the distance between the console and the patient is great enough, a lag effect or latency between end-effector manipulation and the depicted image leads to alterations in movement patterns. The purpose of this study was to determine the effect of visual delay on surgical task performance. At an endoscopic skill station, an analogue delay device was interposed between the surgical field and monitor to delay the transmission of visual information, thus mimicking the distance effect of data transmission. Three surgeons with similar laparoscopic experience participated in the laparoscopic knot tying portion of the study, and seven residents participated in the accuracy and dexterity tasks. The time to complete a single throw was recorded in seconds after adding consecutively increasingly time delay in 50 ms increments. Similar time delay increments were added for the accuracy and dexterity tasks, which involved passing a needle through two adjacent circles and passing a small cylinder through a larger one to reproduce two-handed coordination and spatial resolution. Data were presented as the median time to complete each task. For all three tasks, an incremental increase in time delay was associated with a significant (p < 0.001) increase in the time to complete the task. For dexterity, a statistically significant (p <or= 0.05) delay was identified at 0.25 s of delay from control values without delay. A move-and-wait strategy was gradually adopted up to 0.4 s of visual delay. Compensation for visually delayed image perception occurs on several levels. Initial adaptations include slower end-effector manipulation; late adaptive changes include a move-and-wait strategy. Increased time to perform surgical maneuvers as well as diminished accuracy, diminished dexterity, and increasing fatigue represent additional performance encumbrances evoked by visual time delay. The nuances of both human and digital compensatory mechanisms for visual time delay must be defined and enhanced to maximize the potential for telerobotic surgical applications.

The Effect of Visual System Time Delay on Helicopter Control

There is interest in the development of synthetic visual systems to improve the capability of aircraft to takeoff and land in poor visibility. These systems often have inherent processing delays that can affect a pilot's ability to control an aircraft and a pilot's sense of orientation. The goal of the current study was to determine how much time delay a pilot could tolerate before control was affected, and whether physiological effects would be apparent at the same point. Pilots hovered at a predetermined position in a full flight simulator equipped with a Computer Image Generation (CIG) system and a helmet mounted display. The pilot's visual image was delayed by 67 to 334 milliseconds and varying levels of turbulence were applied to increase the task difficulty. Pilot performance was assessed by collecting objective data on aircraft position error. Handling qualities ratings and reports of physiological symptoms were collected by questionnaire. The results showed that visual time delay increased the variability of position error when as little as 134 ms of delay was encountered. At long delays, sickness symptoms were reported in addition to handing qualities decrements. Turbulence had a minimal effect on performance with long time delays, however it resulted in increased station keeping errors and degraded handling qualities at low delays.

Letter: Binocularly induced motion of flicker patterns.

A new apparent motion phenomenon is described. It occurs when two flashing screens are observed binocularly, one screen for each eye, and the temporal phase between the flashes is suddenly changed. It appears as a low-contrast pattern of vertical stripes that move either to the left or right, depending on the phase of the lights. Changing the relative intensity of the screens alters the effect in a manner consistent with previous measurements on visual time delays.