The relationship between eye position and egocentric visual direction

Hering’s model of egocentric visual direction assumes implicitly that the effect of eye position on direction is both linear and equal for the two eyes; these two assumptions were evaluated in the present experiment. Five subjects pointed (open-loop) to the apparent direction of a target seen under conditions in which the position of one eye was systematically varied while the position of the other eye was held constant. The data were analyzed through examination of the relationship between the variations in perceived egocentric direction and variations inexpected egocentric direction based on the positions of the varying eye. The data revealed that the relationship between eye position and egocentric direction is indeed linear. Further, the data showed that, for some subjects, variations in the positions of the two eyes do not have equateffectsTjn egocentric direction. Both the between-eye differences and the linear relationship may be understood in terms of individual differences in the location of the cyclopean eye, an unequal weighting of the positions of the eyes in the processing of egocentric direction, or some combination of these two factors.     

Saccadic suppression of displacement is strongest in central vision

Perception of target displacement is severely degraded if the displacement occurs during a saccadic eye movement, but the variation of this effect across the visual field is unknown. A small target was displaced from a starting point at the midline, or 10 deg to the right or left, while the eye made a saccade from the 10 deg right position to the 10 deg left position. Saccades were detected and the target displaced on line. Assessed with a signal detection measure, suppression was stronger in central vision than in more peripheral locations for all three subjects. Leftward and rightward displacements yielded equal thresholds. The results complement the findings of others to reveal a picture of perceptual events during saccades, with both deeper saccadic suppression and faster correction of spatial values (the correspondences between retinal position and perceived egocentric direction), favouring more accurate spatial processing in central vision than in the periphery.     

Vertical gaze direction and the resting posture of the eyes

With horizontal gaze, the resting posture of binocular vergence typically corresponds to a distance of about 1 m. The effect of vertical direction of gaze on this basic resting posture was investigated. The dark vergence of twenty-four subjects was measured while they fixated a dim monocular light-point at vertical directions ranging from -45 degree (lowered) to +30 degrees (elevated). In one condition, gaze was varied by changes in eye position with the head held upright; in a second condition, gaze was varied by changes in head inclination with the eyes held in constant (horizontal) position with respect to the head. In both conditions, dark vergence shifted in the convergent (nearer) direction with lowered gaze and in the divergent (farther) direction with elevated gaze. The effect of varied eye inclination was larger, more variable across subjects, and more stable over time than that of varied head inclination. These findings indicate that multiple mechanisms contribute to gaze-related variations of the resting posture of the eyes. They may help to explain the variations of space perception and visual fatigue that are observed with different gaze inclinations.     

Distance perception within near visual space

We investigated the perception of distance of visual targets with constant size and luminance presented between 20 and 120 cm from subjects' eyes. When retinal disparity cues were present, the subjects could reproduce very accurately the distance of a seen reference in this area. When only extraretinal information was available, distance perception was still correct for distances of 40 cm or less. However, distances beyond 60 cm were underestimated. When forced to evaluate the distance between a reference and themselves, e.g. when evaluating the absolute distance or half the distance or twice the distance of a reference, subjects used an egocentric plane of reference located on average 10.4 cm in front of their eyes. Measurements of binocular eye movements indicated a clear relationship between vergence angle and target distance. The egocentric plane of reference at 10.4 cm also corresponds to the maximum achievable vergence. These results suggest that ocular convergence can be used as a reliable cue for distance within the arm's reaching space.     

应用多质-多评价者程序对评定误差的分析

应用多质 -多评价者矩阵分析绩效评定中两种常见误差 -光环效应和自我中心效应。以足球运动员为被评价者 ,以关键事件技术为职务分析方法获得绩效评定特质。以 45名被试观看足球比赛后评定的各职务特质间的相关为基础相关系数 ;两组共 8名被试观看录像剪辑并采用两种评价标准作评价 ,计算各特质评定结果间的相关系数 ,并整理为多质 -多评价者矩阵。结果表明 ,多质 多评价者矩阵可以直观显示光环效应 ;评价者在不同职务的个别特质上表现出自我中心效应。     

Perceptual localization of visual stimuli flashed during saccades

Subjects were asked to make a saccade to a visual target flashed in the dark during a prior primary saccade, and to report its apparent position by moving an adjustable light spot to that position. When targets were presented at the beginning of the primary saccade, subjects perceptually mislocated them in the direction of the saccade, whereas when targets were presented immediately before the end of the primary saccade, the flashed targets were mislocated in the opposite direction. The perceptually localized position of the target was primarily determined by its retinal position. However, at all actual and retinal positions of the target, the localized position shifted from the position that would be predicted if the location of the target was determined only by its retinal position to the prior primary saccade direction. The results were discussed in relation to extraretinal eye position signals. Subjects moved their eyes not to the actual position of the target, but to its apparent position. In some trials, there was a discrepancy between perceptual and oculomotor localization, which was interpreted as having been caused by the imprecise localization ability of the oculomotor system.     

Spatial but not temporal cueing influences the mislocalisation of a target flashed during smooth pursuit

Human subjects misjudge the position of a target that is flashed during a pursuit eye movement. Their judgments are biased in the direction in which the eyes are moving. We investigated whether this bias can be reduced by making the appearance of the flash more predictable. In the normal condition, subjects pursued a moving target that flashed somewhere along its trajectory. After the presentation, they indicated where they had seen the flash. The mislocalisations in this condition were compared to mislocalisations in conditions in which the subjects were given information about when or where the flash would come. This information consisted of giving two warning flashes spaced at equal intervals before the target flash, of giving two warning beeps spaced at equal intervals before the target flash, or of showing the same stimulus twice. Showing the same stimulus twice significantly reduced the mislocalisation. The other conditions did not. We interpret this as indicating that it is not predictability as such that influences the performance, but the fact that the target appears at a spatially cued position. This was supported by a second experiment, in which we examined whether subjects make smaller misjudgments when they have to determine the distance between a target flashed during pursuit and a reference seen previously, than when they have to determine the distance between the flashed target and a reference seen afterwards. This was indeed the case, presumably because the reference provided a spatial cue for the flash when it was presented first. We conclude that a spatial cue reduces the mislocalisation of targets that are flashed during pursuit eye movements. The cue does not have to be exactly at the same position as the flash.     

Upward power tendencies in a hierarchy: Power Distance Theory versus bureaucratic rule

Two contrasting notions concerning upward power tendencies within hierarchically structured groups are investigated. Power Distance Theory assumes that people have a desire for power that results in a tendency to reduce the power distance towards a more powerful other, and this tendency is assumed to be stronger the smaller the power distance. The bureaucratic rule implies that a vacant position may only be taken over by someone from the level immediately below the vacant position. In Experiment 1, power distance from the top position of a hierarchy was manipulated by assigning 120 subjects to a higher or a lower position in a power hierarchy. Results showed that only the motivation derived from the bureaucratic rule (i.e. entitlement) mediated the relationship between power distance and upward tendencies. In Experiment 2, a more pertinent test of the two theoretical notions was performed by assigning 139 subjects to one of three positions. The main results were consistent with the bureaucratic rule: (1) subjects immediately below the top position showed a stronger upward tendency towards this position than subjects in the two lower positions, whereas no differences were found between subjects in these two lower positions; (2) again only entitlement mediated the relationship between power distance and upward tendencies.     

The whereabouts of visual attention: Involuntary attentional bias toward the default gaze direction

This study proposed and verified a new hypothesis on the relationship between gaze direction and visual attention: attentional bias by default gaze direction based on eye-head coordination. We conducted a target identification task in which visual stimuli appeared briefly to the left and right of a fixation cross. In Experiment 1, the direction of the participant’s head (aligned with the body) was manipulated to the left, front, or right relative to a central fixation point. In Experiment 2, head direction was manipulated to the left, front, or right relative to the body direction. This manipulation was based on results showing that bias of eye position distribution was highly correlated with head direction. In both experiments, accuracy was greater when the target appeared at a position where the eyes would potentially be directed. Consequently, eye–head coordination influences visual attention. That is, attention can be automatically biased toward the location where the eyes tend to be directed.     

Induced motion: isolation and dissociation of egocentric and vection-entrained components.

Induced motion (IM) is illusory motion of a stationary test target opposite to the direction of the real motion of the inducing stimulus. We define egocentric IM as an apparent motion of the test target relative to the observer, and vection-entrained IM as an apparent motion of a stationary object along with an apparent motion of the self (vection) induced by the same stimulus. These two forms of IM are often confounded, and tests for distinguishing between them have not been devised. We have devised such tests. Our test for egocentric IM relies on evidence that this form of IM is due mainly to a misregistration of eye movements when optokinetic nystagmus (OKN) is inhibited, and on evidence that OKN is evoked only by stimuli in the plane of convergence. Our test for vection-entrained IM relies on evidence that vection is evoked only by the more distant of two superimposed inducing stimuli. Thus we found egocentric IM to be induced without vection or vection-entrained IM when subjects converged on a foreground moving display with a stationary display in the background, and vection-entrained IM to be induced without egocentric IM when subjects converged on a stationary-foreground display with a moving display in the background. The two types of IM were evoked in opposite directions at the same time when subjects converged on a foreground moving display while a background display moved in the opposite direction. The two forms of IM showed no signs of interaction, and we conclude that they rely on independent motion mechanisms that operate within distinct frames of reference. A control experiment suggested that the depth adjacency effect in IM is determined by the depth adjacency of the inducing stimulus to convergence, not just to the test target.     

Sir Charles Bell on visual direction.

Helmholtz is usually credited with demonstrating the relationship between the perception of visual direction and eye muscle activity: he said that directional judgements resulted from the effort of will involved in altering the position of the eyes. However, Bell reached the same conclusion many years earlier, primarily on the basis of experiments with afterimages: an afterimage appeared to move with voluntary movement of the eye, but it appeared stationary when the eye was moved passively.     

Disturbance of the oculomotor system due to lateral fixation

Three experiments are reported on the effects of previous lateral deviation of the eyes. There is a large effect on their subsequent resting position, and a smaller instantaneous effect on voluntary eye centring. Both are in the direction of previous fixation. The latter effect becomes insignificant within 30 s. The treatment produces errors in visually guided reaching away from the previous direction of fixation. The effects are consistent with a change in registered eye position, an effect also produced by exposure to prisms. Despite this similarity, the disturbance to the oculomotor system caused by these two treatments is sharply differentiated by the resting position. Prisms cause subsequent low frequency, high amplitude oscillations of the eyes (Craske and Templeton, 1968), whereas following lateral deviation the mean resting position returns gradually towards the pre-treatment position.     

Is ‘object-centred neglect’ a homogeneous entity?

The nature of object-centred (allocentric) neglect and the possibility of dissociating it from egocentric (subject-centred) forms of neglect are controversial. Originally, allocentric neglect was described by  and  in patients who reproduced all the elements of a multi-object scene, but left unfinished the left side of one or more of them. More recently, however, Karnath, Mandler, and Clavagnier (2011) have claimed that the severity of allocentric neglect worsens when a complex ‘object’ shifts from an ipsilesional to a contralesional egocentric position. On the basis of these and of other clinical data, showing that allocentric and egocentric neglect are strongly associated, they have questioned the possibility of dissociating these two forms of neglect, suggesting that egocentric and allocentric neglect constitute different manifestations of the same disturbed system. Since these statements were inconsistent with the clinical findings which had prompted the construct of object-centred neglect, we checked in a group of right brain-damaged patients, who had copied the original multi-object scene, if the degree of neglect for the left side of figures varied as a function of their position on the horizontal axis. Furthermore, we reviewed all papers where copies of other multi-object scenes had been reported. Results of both studies failed to confirm the assumption of a relationship between spatial location of the stimulus and severity of object-centred neglect. This discrepancy between our data and those obtained by Karnath et al. (2011) could be due to the characteristics of stimuli and of procedures used to evaluate ‘object-centred’ neglect. If the stimulus is complex and the task requires its thorough exploration, the spatial location of the stimulus will influence the severity of ‘object-centred neglect’. If, on the contrary, the stimulus is simple and can be identified with few eye fixations, the spatial location of the stimulus should not influence the severity of ‘object-centred neglect’. In any case, our data confirm the possibility of dissociating allocentric from egocentric neglect.     

The underestimation of egocentric distance: evidence from frontal matching tasks

There is controversy over the existence, nature, and cause of error in egocentric distance judgments. One proposal is that the systematic biases often found in explicit judgments of egocentric distance along the ground may be related to recently observed biases in the perceived declination of gaze (Durgin & Li, Attention, Perception, & Psychophysics, in press), To measure perceived egocentric distance nonverbally, observers in a field were asked to position themselves so that their distance from one of two experimenters was equal to the frontal distance between the experimenters. Observers placed themselves too far away, consistent with egocentric distance underestimation. A similar experiment was conducted with vertical frontal extents. Both experiments were replicated in panoramic virtual reality. Perceived egocentric distance was quantitatively consistent with angular bias in perceived gaze declination (1.5 gain). Finally, an exocentric distance-matching task was contrasted with a variant of the egocentric matching task. The egocentric matching data approximate a constant compression of perceived egocentric distance with a power function exponent of nearly 1; exocentric matches had an exponent of about 0.67. The divergent pattern between egocentric and exocentric matches suggests that they depend on different visual cues.     

The rod-and-frame illusion in erect and supine observers

Previous studies have found that the effect of a tilted frame on egocentric rod adjustments is greater when an overhead display in a horizontal plane is viewed from a supine body position than when a vertical display is viewed from an erect body position. The present studies were designed to see whether this phenomenon could be attributed to an intravisual orientation contrast effect or to the effects of visually induced eye torsion. No significant erect-supine differences were found on measures of either effect. Errors in the direction of frame tilt were significantly greater in the supine position when observers were asked to align a visible rod or an unseen hand-held disk with the head, but no effect of body position was found in matching the orientation of the disk with the rod. The data suggest that erect-supine differences in frame effects are not attributable simply to intravisual factors. The results are discussed in terms used by Harris (1974) to describe “straight-ahead shifts” in judging spatial directions with respect to the median plane.     

Coordinated flexibility: how initial gaze position modulates eye-hand coordination and reaching

Reaching to targets in space requires the coordination of eye and hand movements. In two experiments, we recorded eye and hand kinematics to examine the role of gaze position at target onset on eye-hand coordination and reaching performance. Experiment 1 showed that with eyes and hand aligned on the same peripheral start location, time lags between eye and hand onsets were small and initiation times were substantially correlated, suggesting simultaneous control and tight eye-hand coupling. With eyes and hand departing from different start locations (gaze aligned with the center of the range of possible target positions), time lags between eye and hand onsets were large and initiation times were largely uncorrelated, suggesting independent control and decoupling of eye and hand movements. Furthermore, initial gaze position strongly mediated manual reaching performance indexed by increments in movement time as a function of target distance. Experiment 2 confirmed the impact of target foveation in modulating the effect of target distance on movement time. Our findings reveal the operation of an overarching, flexible neural control system that tunes the operation and cooperation of saccadic and manual control systems depending on where the eyes look at target onset.     

Arrows don’t look at you: Qualitatively different attentional mechanisms triggered by gaze and arrows

Eye gaze conveys rich information concerning the states of mind of others, playing a critical role in social interactions, signaling internal states, and guiding others’ attention. On the basis of its social significance, some researchers have proposed that eye gaze may represent a unique attentional stimulus. However, contrary to this notion, the majority of the literature has shown indistinguishable attentional effects when eye gaze and arrows have been used as cues. Taking a different approach, in this study we aimed at finding qualitative attentional differences between gazes and arrows when they were used as targets instead of as cues. We used a spatial Stroop task, in which participants were required to identify the direction of eyes or arrows presented to the left or the right of a fixation point. The results showed that the two types of stimuli led to opposite spatial interference effects, with arrows producing faster reaction times when the stimulus direction was congruent with the stimulus position (a typical spatial Stroop effect), and eye gaze producing faster reaction times when it was incongruent (a “reversed” spatial Stroop effect). This reversed Stroop is interpreted as an eye-contact effect, therefore revealing the unique nature of eyes as special social-attention stimuli.     

Interactions between goal-directed eye and arm movements: arguments for an interdependent motor control

The accuracy of movements of the arm directed toward a point in space was investigated in healthy human subjects. To study the influence of the eye movement itself, on the guidance of the arm in the absence of any visual context, subjects performed the goal-directed arm movements without visual feedback about the arm displacement and the target position. The subjects were asked either to keep their eyes centered or oriented toward a previously flashed target. The analysis of the distribution of the errors in arm final position in the two conditions suggests that the eye movement influences the final position adopted by the arm. It is postulated that an interaction exists between the eye and arm systems during the motor program elaboration phase.     

Importance of head movements in gaze tracking during table tennis forehand stroke

The purpose of this study was to clarify the properties of gaze and head movements during forehand stroke in table tennis. Collegiate table tennis players (n = 12) conducted forehand strokes toward a ball launched by a skilled experimenter. A total of ten trials were conducted for the experimental task. Horizontal and vertical movements of the ball, gaze, head and eye were analyzed from the image recorded by an eye tracking device. The results showed that participants did not always keep their gaze and head position on the ball throughout the entire ball path. Our results indicate that table tennis players tend to gaze at the ball in the initial ball-tracking phase. Furthermore, there was a significant negative correlation between eye and head position especially in the vertical direction. This result suggests that horizontal VOR is suppressed more than vertical VOR in ball-tracking during table tennis forehand stroke. Finally, multiple regression analysis showed that the effect of head position to gaze position was significantly higher than that of eye position. This result indicates that gaze position during forehand stroke could be associated with head position rather than eye position. Taken together, head movements may play an important role in maintaining the ball in a constant egocentric direction in table tennis forehand stroke.