Induced rotary motion and ocular torsion

Ocular torsion is related to perceived motion-induced position shifts

Ocular torsion (i.e., rotations of the eye about the line of sight) can be induced by visual rotational motion. It remains unclear whether and how such visually induced torsion is related to perception. By using the flash-grab effect, an illusory position shift of a briefly flashed stationary target superimposed on a rotating pattern, we examined the relationship between torsion and perception. In two experiments, 25 observers reported the perceived location of a flash while their three-dimensional eye movements were recorded. In Experiment 1, the flash coincided with a direction reversal of a large, centrally displayed, rotating grating. The grating triggered visually induced torsion in the direction of stimulus rotation. The magnitude of torsional eye rotation correlated with the illusory perceptual position shift. To test whether torsion caused the illusion, in Experiment 2, the flash was superimposed on two peripheral gratings rotating in opposite directions. Even though torsion was eliminated, the illusory position shift persisted. Despite the lack of a causal relationship, the torsion-perception correlations indicate a close link between both systems, either through similar visual-input processing or a boost of visual rotational signal strength via oculomotor feedback.

High-accuracy measurement of rotational eye movement by tracking of blood vessel images

This study focuses on a technique for measuring the angle of rotational eye movement by tracking the conjunctival blood vessel ends of sclera, instead of grayscale iris patterns used in the existing techniques. It is because the blood vessel images of sclera have high grayscale contrasts. This technique especially recognizes the contour of the iris to detect the target conjunctival blood vessel end and use the degree of similarity by means of template matching to select automatically the blood vessel end to be tracked. The search region is limited by template matching to achieve low processing cost and high accuracy and resolution even when the background light varies.

The initial torsional Ocular Following Response (tOFR) in humans: a response to the total motion energy in the stimulus?

We recorded the initial torsional Ocular Following Responses (tOFRs) elicited at short latency by visual images that occupied the frontal plane and rotated about the lines of sight. Using 1-D radial gratings, the local spatio-temporal characteristics of these tOFRs closely resembled those we previously reported for the hOFRs to horizontal motion with 1-D vertical gratings. When the 1-D radial grating was subdivided into a number of concentric annuli, each with the same radial thickness, tOFRs were less than predicted from the sum of the responses to the individual annuli: spatial normalization. However, the normalization was much weaker than that which we previously reported for the hOFRs. Further, when the number, thickness and contrast of these concentric annuli were varied systematically, the latency and magnitude of the tOFRs were well described by single monotonic functions when plotted against the product of the total area of the annuli and the square of their Michelson contrast ("A*C(2)"), consistent with the hypothesis that the onset and magnitude of the initial tOFR are determined by the total motion energy in the stimulus. When our previously published hOFR data were plotted against A*C(2), a single monotonic function sufficed to describe the latency but not the magnitude.

Tolerance of stereopsis to conjunctive cyclorotation

Stereopsis is largely unperturbed by various types of eye, head, and target movements. Here, we used a simple setup to investigate the limits of a previously untested type of stimulus motion on stereoscopic depth perception. Clockwise and counterclockwise rotations of an autostereogram were used to describe the limits of stereopsis to roll-tilt. The result showed intact depth perception with stimulus rotation up to approximately 12 degrees, regardless of rotation direction and viewing distance, indicating a tolerant mechanism for stereoscopic processing by the human neural system.

Attending to a misoriented word causes the eyeball to rotate in the head

Torsional eye movements are triggered by head tilt and a rotating visual field. We examined whether attention to a misoriented form could also induce torsion. Thirty-six observers viewed an adapting field containing a bright vertical line, and then they viewed a display that was composed of two misoriented words (one rotated clockwise, the other counterclockwise, by 15 degrees, 30 degrees, or 45 degrees). The subjects were instructed to attend to one of the words. The subjects' adjustments of a reference line to match the tilt of the afterimage showed that attention to a misoriented word produces torsional eye movement (verified with direct measurements on 4 additional subjects). This eye movement reduces the retinal misorientation of the word by about 1 degrees. The results of this study reinforce the linkage between selective attention and eye movements and may provide a useful tool for dissecting different forms of "mental rotation" and other adjustments in internal reference frames. Apparent-motion displays confirming that the eye rotated in the head may be downloaded from www.psychonomic.org/archive.

Changes in ocular torsion position produced by a single visual line rotating around the line of sight––visual “entrainment” of ocular torsion

A large- or full-field visual stimulus slowly rotating around the naso-occipital axis of an observer causes both eyes to tort, and many of the factors controlling this optokinetic torsional response have been identified. The present study reports that a single line rotating about the line of sight can cause both eyes to tort in the same direction as the stimulus but with a low gain. We have used the term 'entrainment' to describe this torsional response. This paper reports some of the factors associated with entrainment. Video measures of 3-d eye position were recorded while the subject made settings of a simple visual line to subjective visual horizontal (SVH) and vertical (SVV) using the standard method-of-adjustment paradigm. The visual line was composed of 11 light-emitting diodes; the line subtended a visual angle of 19 degrees, and moved at a constant speed of 4.8 degrees /s. Settings were made in an otherwise darkened room, and also in the light. Subjects were required to maintain fixation of the central LED while making settings from starting positions 10 or 20 degrees either side of gravitational horizontal or vertical. We show that entrainment of ocular torsion by the single moving visual line is low in gain but a reliable and repeatable effect and that (1) there are considerable individual differences between subjects but within-subject consistency, (2) all subjects show larger and more consistent torsional entrainment for lines moving to SVH than lines moving to SVV, (3) the strongest entrainment generally occurs within about 10 degrees of the target position, and (4) entrainment is also present in the light, though with slightly reduced gain.

Perception of self-motion from peripheral optokinetic stimulation suppresses visual evoked responses to central stimuli

In a previous functional neuroimaging study we found that early visual areas deactivated when a rotating optical flow stimulus elicited the illusion of self-motion (vection) compared with when it was perceived as a moving object. Here, we investigated whether electrical cortical responses to an independent central visual probe stimulus change as a function of whether optical flow stimulation in the periphery induces the illusion of self-motion or not. Visual-evoked potentials (VEPs) were obtained in response to pattern-reversals in the central visual field in the presence of a constant peripheral large-field optokinetic stimulus that rotated around the naso-occipital axis and induced intermittent sensations of vection. As control, VEPs were also recorded during a stationary peripheral stimulus and showed no difference than those obtained during optokinetic stimulation. The VEPs during constant peripheral stimulation were then divided into two groups according to the time spans where the subjects reported object- or self-motion, respectively. The N70 VEP component showed a significant amplitude reduction when, due to the peripheral stimulus, subjects experienced self-motion compared to when the peripheral stimulus was perceived as object-motion. This finding supplements and corroborates our recent evidence from functional neuroimaging that early visual cortex deactivates when a visual flow stimulus elicits the illusion of self-motion compared with when the same sensory input is interpreted as object-motion. This dampened responsiveness might reflect a redistribution of sensorial and attentional resources when the monitoring of self-motion relies on a sustained and veridical processing of optic flow and may be compromised by other sources of visual input.

Induced rotational motion with nonabutting inducing and induced stimuli: implications regarding two forms of induced motion

Induced motion is the illusory motion of a static stimulus in the opposite direction to a moving stimulus. Two types of induced motion have been distinguished: (a) when the moving stimulus is distant from the static stimulus and undergoes overall displacement, and (b) when the moving stimulus is pattern viewed within fixed boundaries that abut the static stimulus. Explanations of the 1st type of induced motion refer to mediating phenomena, such as vection, whereas the 2nd type is attributed to local processing by motion-sensitive neurons. The present research was directed to a display that elicited induced rotational motion with the characteristics of both types of induced motion: the moving stimulus lay within fixed boundaries, but the inducing and induced stimuli were distant from each other. The author investigated the properties that distinguished the two types of induced motion. In 3 experiments, induced motion persisted indefinitely, interocular transfer of the aftereffect of induced motion was limited to about 20%, and the time-course of the aftereffect of induced motion could not be attributed to vection. Those results were consistent with fixed-boundary induced motion. However, they could not be explained by local processing. Instead, the results might reflect the detection of object motion within a complex flow-field that resulted from the observer's motion.

Image processing for improved eye-tracking accuracy

Video cameras provide a simple, noninvasive method for monitoring a subject's eye movements. An important concept is that of the resolution of the system, which is the smallest eye movement that can be reliably detected. While hardware systems are available that estimate direction of gaze in real-time from a video image of the pupil, such systems must limit image processing to attain real-time performance and are limited to a resolution of about 10 arc minutes. Two ways to improve resolution are discussed. The first is to improve the image processing algorithms that are used to derive an estimate. Off-line analysis of the data can improve resolution by at least one order of magnitude for images of the pupil. A second avenue by which to improve resolution is to increase the optical gain of the imaging setup (i.e., the amount of image motion produced by a given eye rotation). Ophthalmoscopic imaging of retinal blood vessels provides increased optical gain and improved immunity to small head movements but requires a highly sensitive camera. The large number of images involved in a typical experiment imposes great demands on the storage, handling, and processing of data. A major bottleneck had been the real-time digitization and storage of large amounts of video imagery, but recent developments in video compression hardware have made this problem tractable at a reasonable cost. Images of both the retina and the pupil can be analyzed successfully using a basic toolbox of image-processing routines (filtering, correlation, thresholding, etc.), which are, for the most part, well suited to implementation on vectorizing supercomputers.

The effects of visual depth and eccentricity on manual bias, induced motion, and vection

The relationship between the effects of visual-surround roll motion on compensatory manual tracking of a central display and the perceptual phenomena of induced motion and vection were investigated. To determine if manual-control biases generated in the direction of surround rotation compensate primarily for the perceived counterrotation of the central display ('induced motion') or the perceived counterrotation of the entire body ('vection'), the depth and eccentricity of the visual surround were varied. In the first experiment, twelve subjects attempted to keep an unstable central display level while viewing rotating visual surrounds in three depth planes: near (approximately 20 cm in front of the central display), coplanar, and far (approximately 21 cm behind the central display). In the second experiment, twelve additional subjects viewed a rotating surround that was presented either in the full visual field (0-110 deg) or in central and peripheral regions of similar width. Manual-control biases and induced motion were shown to be closely related to one another and strongly influenced both by central and by peripheral surround motion at or beyond the plane of fixation. Vection, on the other hand, was shown to be much more dependent on peripheral visual inputs.