Extraretinal and retinal amplitude and phase errors during Filehne illusion and path perception

Pursuit eye movements give rise to retinal motion. To judge stimulus motion relative to the head, the visual system must correct for the eye movement by using an extraretinal, eye-velocity signal. Such correction is important in a variety of motion estimation tasks including judgments of object motion relative to the head and judgments of self-motion direction from optic flow. The Filehne illusion (where a stationary object appears to move opposite to the pursuit) results from a mismatch between retinal and extraretinal speed estimates. A mismatch in timing could also exist. Speed and timing errors were investigated using sinusoidal pursuit eye movements. We describe a new illusion--the slalom illusion--in which the perceived direction of self-motion oscillates left and right when the eyes move sinusoidally. A linear model is presented that determines the gain ratio and phase difference of extraretinal and retinal signals accompanying the Filehne and slalom illusions. The speed mismatch and timing differences were measured in the Filehne and self-motion situations using a motion-nulling procedure. Timing errors were very small for the Filehne and slalom illusions. However, the ratios of extraretinal to retinal gain were consistently less than 1, so both illusions are the consequence of a mismatch between estimates of retinal and extraretinal speed. The relevance of the results for recovering the direction of self-motion during pursuit eye movements is discussed.     

Retinal and extraretinal information in movement perception: how to invert the Filehne illusion

During a pursuit eye movement made in darkness across a small stationary stimulus, the stimulus is perceived as moving in the opposite direction to the eyes. This so-called Filehne illusion is usually explained by assuming that during pursuit eye movements the extraretinal signal (which informs the visual system about eye velocity so that retinal image motion can be interpreted) falls short. A study is reported in which the concept of an extraretinal signal is replaced by the concept of a reference signal, which serves to inform the visual system about the velocity of the retinae in space. Reference signals are evoked in response to eye movements, but also in response to any stimulation that may yield a sensation of self-motion, because during self-motion the retinae also move in space. Optokinetic stimulation should therefore affect reference signal size. To test this prediction the Filehne illusion was investigated with stimuli of different optokinetic potentials. As predicted, with briefly presented stimuli (no optokinetic potential) the usual illusion always occurred. With longer stimulus presentation times the magnitude of the illusion was reduced when the spatial frequency of the stimulus was reduced (increased optokinetic potential). At very low spatial frequencies (strongest optokinetic potential) the illusion was inverted. The significance of the conclusion, that reference signal size increases with increasing optokinetic stimulus potential, is discussed. It appears to explain many visual illusions, such as the movement aftereffect and center-surround induced motion, and it may bridge the gap between direct Gibsonian and indirect inferential theories of motion perception.     

Perception of self-motion from visual flow

Accurate and efficient control of self-motion is an important requirement for our daily behavior. Visual feedback about self-motion is provided by optic flow. Optic flow can be used to estimate the direction of self-motion (‘heading’) rapidly and efficiently. Analysis of oculomotor behavior reveals that eye movements usually accompany self-motion. Such eye movements introduce additional retinal image motion so that the flow pattern on the retina usually consists of a combination of self-movement and eye movement components. The question of whether this ‘retinal flow’ alone allows the brain to estimate heading, or whether an additional ‘extraretinal’ eye movement signal is needed, has been controversial. This article reviews recent studies that suggest that heading can be estimated visually but extraretinal signals are used to disambiguate problematic situations. The dorsal stream of primate cortex contains motion processing areas that are selective for optic flow and self-motion. Models that link the properties of neurons in these areas to the properties of heading perception suggest possible underlying mechanisms of the visual perception of self-motion.     

Retinal flow is sufficient for steering during observer rotation

How do people control locomotion while their eyes are simultaneously rotating? A previous study found that during simulated rotation, they can perceive a straight path of self-motion from the retinal flow pattern, despite conflicting extraretinal information, on the basis of dense motion parallax and reference objects. Here we report that the same information is sufficient for active control ofjoystick steering. Participants steered toward a target in displays that simulated a pursuit eye movement. Steering was highly inaccurate with a textured ground plane (motion parallax alone), but quite accurate when an array of posts was added (motion parallax plus reference objects). This result is consistent with the theory that instantaneous heading is determined from motion parallax, and the path of self-motion is determined by updating heading relative to environmental objects. Retinal flow is thus sufficient for both perceiving self-motion and controlling self-motion with a joystick; extraretinal and positional information can also contribute, but are not necessary.     

Motion versus position in the perception of head-centred movement

Abstract. Observers can recover motion with respect to the head during an eye movement by comparing signals encoding retinal motion and the velocity of pursuit. Evidently there is a mismatch between these signals because perceived head-centred motion is not always veridical. One example is the Filehne illusion, in which a stationary object appears to move in the opposite direction to pursuit. Like the motion aftereffect, the phenomenal experience of the Filehne illusion is one in which the stimulus moves but does not seem to go anywhere. This raises problems when measuring the illusion by motion nulling because the more traditional technique confounds perceived motion with changes in perceived position. We devised a new nulling technique using global-motion stimuli that degraded familiar position cues but preserved cues to motion. Stimuli consisted of random-dot patterns comprising signal and noise dots that moved at the same retinal 'base' speed. Noise moved in random directions. In an eye-stationary speed-matching experiment we found noise slowed perceived retinal speed as 'coherence strength' (ie percentage of signal) was reduced. The effect occurred over the two-octave range of base speeds studied and well above direction threshold. When the same stimuli were combined with pursuit, observers were able to null the Filehne illusion by adjusting coherence. A power law relating coherence to retinal base speed fit the data well with a negative exponent. Eye-movement recordings showed that pursuit was quite accurate. We then tested the hypothesis that the stimuli found at the null-points appeared to move at the same retinal speed. Two observers supported the hypothesis, a third partially, and a fourth showed a small linear trend. In addition, the retinal speed found by the traditional Filehne technique was similar to the matches obtained with the global-motion stimuli. The results provide support for the idea that speed is the critical cue in head-centred motion perception.     

An acceleration illusion caused by underestimation of stimulus velocity during pursuit eye movements: Aubert-Fleischl revisited

When the eyes pursue a fixation point that sweeps across a moving background pattern, and the fixation point is suddenly made to stop, the ongoing motion of the background pattern seems to accelerate to a higher velocity. Experiment I showed that this acceleration illusion is not caused by the sudden change in (i) the relative velocity between background and fixation point, (ii) the velocity of the retinal image of the background pattern, or (iii) the motion of the retinal image of the rims of the CRT screen on which the experiment was carried out. In experiment II the magnitude of the illusion was quantified. It is strongest when background and eyes move in the same direction. When they move in opposite directions it becomes less pronounced (and may disappear) with higher background velocities. The findings are explained in terms of a model proposed by the first author, in which the perception of object motion and velocity derives from the interaction between retinal slip velocity information and the brain's 'estimate' of eye velocity in space. They illustrate that the classic Aubert-Fleischl phenomenon (a stimulus seems to be moving slower when pursued with the eyes than when moving in front of stationary eyes) is a special case of a more general phenomenon: whenever we make a pursuit eye movement we underestimate the velocity of all stimuli in our visual field which happen to move in the same direction as our eyes, or which move slowly in the direction opposite to our eyes.     

Additivity of retinal and pursuit velocity in the perceptions of depth and rigidity from object-produced motion parallax

Two psychophysical experiments were conducted to investigate the mechanism that generates stable depth structure from retinal motion combined with extraretinal signals from pursuit eye movements. Stimuli consisted of random dots that moved horizontally in one direction (ie stimuli had common motion on the retina), but at different speeds between adjacent rows. The stimuli were presented with different speeds of pursuit eye movements whose direction was opposite to that of the common retinal motion. Experiment 1 showed that the rows moving faster on the retina appeared closer when viewed without eye movements; however, they appeared farther when pursuit speed exceeded the speed of common retinal motion. The 'transition' speed of the pursuit eye movement was slightly, but consistently, larger than the speed of common retinal motion. Experiment 2 showed that parallax thresholds for perceiving relative motion between adjacent rows were minimum at the transition speed found in experiment 1. These results suggest that the visual system calculates head-centric velocity, by adding retinal velocity and pursuit velocity, to obtain a stable depth structure.     

Cognitive processes involved in smooth pursuit eye movements

Ocular pursuit movements allow moving objects to be tracked with a combination of smooth movements and saccades. The principal objective is to maintain smooth eye velocity close to object velocity, thus minimising retinal image motion and maintaining acuity. Saccadic movements serve to realign the image if it falls outside the fovea, the area of highest acuity. Pursuit movements are often portrayed as voluntary but their basis lies in processes that sense retinal motion and can induce eye movements without active participation. The factor distinguishing pursuit from such reflexive movements is the ability to select and track a single object when presented with multiple stimuli. The selective process requires attention, which appears to raise the gain for the selected object and/or suppress that associated with other stimuli, the resulting competition often reducing pursuit velocity. Although pursuit is essentially a feedback process, delays in motion processing create problems of stability and speed of response. This is countered by predictive processes, probably operating through internal efference copy (extra-retinal) mechanisms using short-term memory to store velocity and timing information from prior stimulation. In response to constant velocity motion, the initial response is visually driven, but extra-retinal mechanisms rapidly take over and sustain pursuit. The same extra-retinal mechanisms may also be responsible for generating anticipatory smooth pursuit movements when past experience creates expectancy of impending object motion. Similar, but more complex, processes appear to operate during periodic pursuit, where partial trajectory information is stored and released in anticipation of expected future motion, thus minimising phase errors associated with motion processing delays.     

Cognitive processes involved in smooth pursuit eye movements

Ocular pursuit movements allow moving objects to be tracked with a combination of smooth movements and saccades. The principal objective is to maintain smooth eye velocity close to object velocity, thus minimising retinal image motion and maintaining acuity. Saccadic movements serve to realign the image if it falls outside the fovea, the area of highest acuity. Pursuit movements are often portrayed as voluntary but their basis lies in processes that sense retinal motion and can induce eye movements without active participation. The factor distinguishing pursuit from such reflexive movements is the ability to select and track a single object when presented with multiple stimuli. The selective process requires attention, which appears to raise the gain for the selected object and/or suppress that associated with other stimuli, the resulting competition often reducing pursuit velocity. Although pursuit is essentially a feedback process, delays in motion processing create problems of stability and speed of response. This is countered by predictive processes, probably operating through internal efference copy (extra-retinal) mechanisms using short-term memory to store velocity and timing information from prior stimulation. In response to constant velocity motion, the initial response is visually driven, but extra-retinal mechanisms rapidly take over and sustain pursuit. The same extra-retinal mechanisms may also be responsible for generating anticipatory smooth pursuit movements when past experience creates expectancy of impending object motion. Similar, but more complex, processes appear to operate during periodic pursuit, where partial trajectory information is stored and released in anticipation of expected future motion, thus minimising phase errors associated with motion processing delays.     

The neural basis of smooth pursuit eye movements in the rhesus monkey brain

Smooth pursuit eye movements are performed in order to prevent retinal image blur of a moving object. Rhesus monkeys are able to perform smooth pursuit eye movements quite similar as humans, even if the pursuit target does not consist in a simple moving dot. Therefore, the study of the neuronal responses as well as the consequences of micro-stimulation and lesions in trained monkeys performing smooth pursuit is a powerful approach to understand the human pursuit system. The processing of visual motion is achieved in the primary visual cortex and the middle temporal area. Further processing including the combination of retinal image motion signals with extra-retinal signals such as the ongoing eye and head movement occurs in subsequent cortical areas as the medial superior temporal area, the ventral intraparietal area and the frontal and supplementary eye field. The frontal eye field especially contributes anticipatory signals which have a substantial influence on the execution of smooth pursuit. All these cortical areas send information to the pontine nuclei, which in turn provide the input to the cerebellum. The cerebellum contains two pursuit representations: in the paraflocculus/flocculus region and in the posterior vermis. While the first representation is most likely involved in the coordination of pursuit and the vestibular-ocular reflex, the latter is involved in the precise adjustments of the eye movements such as adaptation of pursuit initiation. The output of the cerebellum is directed to the moto-neurons of the extra-ocular muscles in the brainstem.     

Task-irrelevant sounds influence both temporal order and apparent-motion judgments about tactile stimuli applied to crossed and uncrossed hands

It has been suggested that judgments about the temporal–spatial order of successive tactile stimuli depend on the perceived direction of apparent motion between them. Here we manipulated tactile apparent-motion percepts by presenting a brief, task-irrelevant auditory stimulus temporally in-between pairs of tactile stimuli. The tactile stimuli were applied one to each hand, with varying stimulus onset asynchronies (SOAs). Participants reported the location of the first stimulus (temporal order judgments: TOJs) while adopting both crossed and uncrossed hand postures, so we could scrutinize skin-based, anatomical, and external reference frames. With crossed hands, the sound improved TOJ performance at short (≤300 ms) and at long (>300 ms) SOAs. When the hands were uncrossed, the sound induced a decrease in TOJ performance, but only at short SOAs. A second experiment confirmed that the auditory stimulus indeed modulated tactile apparent motion perception under these conditions. Perceived apparent motion directions were more ambiguous with crossed than with uncrossed hands, probably indicating competing spatial codes in the crossed posture. However, irrespective of posture, the additional sound tended to impair potentially anatomically coded motion direction discrimination at a short SOA of 80 ms, but it significantly enhanced externally coded apparent motion perception at a long SOA of 500 ms. Anatomically coded motion signals imply incorrect TOJ responses with crossed hands, but correct responses when the hands are uncrossed; externally coded motion signals always point toward the correct TOJ response. Thus, taken together, these results suggest that apparent-motion signals are likely taken into account when tactile temporal–spatial information is reconstructed.

     

注意促进运动知觉判断的时间进程

本研究通过控制深度视觉线索, 分析3D SFM (structure from motion)知觉中的眼动特征, 探讨注意对SFM知觉判断的影响及其时间进程。结果显示, 有线索刺激比模糊刺激的判断更加快、更加肯定(百分比更高); 眼睛移动方向和微眼跳方向都分别与知觉判断的运动方向具有一致性; 微眼跳频次、峰速度和幅度也都分别表现出深度线索的促进效应。实验结果表明, SFM知觉过程大致分为速度计算和构建三维结构两个阶段; 注意对SFM知觉的调节作用主要发生在构建三维结构阶段; 注意从150 ms开始指向选择对象, 驻留持续约200 ms后, 从局部运动矢量流转移到整体运动方向的知觉判断。     

Coherent modulation of stimulus colour can affect visually induced self-motion perception

The effects of dynamic colour modulation on vection were investigated to examine whether perceived variation of illumination affects self-motion perception. Participants observed expanding optic flow which simulated their forward self-motion. Onset latency, accumulated duration, and estimated magnitude of the self-motion were measured as indices of vection strength. Colour of the dots in the visual stimulus was modulated between white and red (experiment 1), white and grey (experiment 2), and grey and red (experiment 3). The results indicated that coherent colour oscillation in the visual stimulus significantly suppressed the strength of vection, whereas incoherent or static colour modulation did not affect vection. There was no effect of the types of the colour modulation; both achromatic and chromatic modulations turned out to be effective in inhibiting self-motion perception. Moreover, in a situation where the simulated direction of a spotlight was manipulated dynamically, vection strength was also suppressed (experiment 4). These results suggest that observer's perception of illumination is critical for self-motion perception, and rapid variation of perceived illumination would impair the reliabilities of visual information in determining self-motion.     

The role of the saccade target object in the perception of a visually stable world

Although the proximal stimulus shifts position on our retinae with each saccade, we perceive our world as stable and continuous. Most theories of visual stability implicitly assume a mechanism that spatially adjusts perceived locations associated with the retinal array by using, as a parameter, extra-retinal eye position information, a signal that encodes the size and direction of the saccade. The results from the experiment reported in this article challenge this idea. During a participant's saccade to a target object, one of the following was displaced: the entire scene, the target object, or the background behind the target object. Participants detected the displacement of the target object twice as frequently as the displacement of the entire background. The direction of displacement relative to the saccade also affected detectability. We use a new theory, the saccade target theory (McConkie & Currie, 1996), to interpret these results. This theory proposes that retinal (as opposed to extra-retinal) factors, primarily those concerning the saccade target object, are critical for the detection of intrasaccadic stimulus shifts.     

Distractor interference during smooth pursuit eye movements

When 2 targets for pursuit eye movements move in different directions, the eye velocity follows the vector average (S. G. Lisberger & V. P. Ferrera, 1997). The present study investigates the mechanisms of target selection when observers are instructed to follow a predefined horizontal target and to ignore a moving distractor stimulus. Results show that at 140 ms after distractor onset, horizontal eye velocity is decreased by about 25%. Vertical eye velocity increases or decreases by 1 degrees /s in the direction opposite from the distractor. This deviation varies in size with distractor direction, velocity, and contrast. The effect was present during the initiation and steady-state tracking phase of pursuit but only when the observer had prior information about target motion. Neither vector averaging nor winner-take-all models could predict the response to a moving to-be-ignored distractor during steady-state tracking of a predefined target. The contributions of perceptual mislocalization and spatial attention to the vertical deviation in pursuit are discussed.     

Depth separation between foreground and background on visually induced perception of self-motion

A uniformly moving visual pattern can induce observer's self-motion perception in the opposite direction (vection), and an additional static stimulus can modulate (facilitate or inhibit) the strength of it. The present study was designed to investigate the effects of stimulus depth order and the depth distances of the visual stimulus on the inhibition and facilitation of vection caused by the additional static stimulus, measuring duration and estimated magnitude of vection as indices of vection strength. Analysis of this psychophysical experiment with four participants indicated that the static foreground presented in front of the moving pattern can facilitate vection, whereas the static background inhibits it (Duration: F1,3= 12.06, p<.05; Estimation: F1,3= 13.87, p<.05). Furthermore, the depth distances from the observer or the depth separation between the foreground and the background did not affect the self-motion perception (F2,6 < 1.0 for duration and estimation).     

The Linkage of Visual Motion Signals

Recovering a reliable 3D percept from the retinal sampling of dynamic images requires the linkage of motion signals across space and time. In this paper, we review recent experimental results that enhance our understanding of the perceptual processes of motion integration, segmentation, and selection that are necessary to solve this inverse optics problem. Simple paradigms involving the presentation of moving contours are used to assess our ability to link sparse motion information. Our results indicate that human motion perception strongly depends on both primitive stimulus characteristics, such as contrast, eccentricity, and duration, as well as higher level characteristics such as feature classification and spatial configurations. Further, the perceived direction of a moving object depends little upon its familiarity. Finally, pursuit eye movements of compositional stimuli are highly correlated with perceived motion coherence. This ensemble of results is analysed within the context of current theories of motion perception.     

Retinal masking during pursuit eye movements: implications for spatiotopic visual persistence

White (1976) reported that presentation of a masking stimulus during a pursuit eye movement interfered with the perception of a target stimulus that shared the same spatial, rather than retinal, coordinates as the mask. This finding has been interpreted as evidence for the existence of spatiotopic visual persistence. We doubted White's results because they implied a high degree of position constancy during pursuit eye movements, contrary to previous research, and because White did not monitor subjects' eye position during pursuit; if White's subjects did not make continuous pursuit eye movements, it might appear that masking was spatial when in fact it was retinal. We attempted to replicate White's results and found that when eye position was monitored to ensure that subjects made continuous pursuit movements, masking was retinal rather than spatial. Subjects' phenomenal impressions also indicated that retinal, rather than spatial, factors underlay performance in this task. The implications of these and other results regarding the existence of spatiotopic visual persistence are discussed.     

Extraretinal information about eye position during involuntary eye movement: optokinetic afternystagmus

Despite importance for theories of perception, controversy exists as to whether information is available to the perceptual system about involuntary as well as voluntary eye movements. We measured the perceived direction of targets flashed briefly in an otherwise dark field during the primary phase of optokinetic afternystagmus (OKAN), an involuntary eye movement that persists in darkness following optokinetic stimulation. Perceived direction was measured by unseen pointing in one experiment and by pointing made under visual control in a second experiment. Pointing was essentially veridical in both experiments, indicating that accurate extra-retinal information about eye position (presumably, as efference copy) exists for OKAN. Illusory motion of visual targets, which can occur during involuntary oculomotor responses, therefore cannot be attributed to a lack of efference-copy signals for such eye movements.     

Why eye movements and perceptual factors have to be controlled in studies on "representational momentum"

In order to study memory of the final position of a smoothly moving target, Hubbard (e.g., Hubbard and Bharucha, 1988) presented smooth stimulus motion and used motor responses. In contrast, Freyd (e.g., Freyd and Finke, 1984) presented implied stimulus motion and used the method of constant stimuli. The same forward error was observed in both paradigms. However, the processes underlying the error may be very different. When smooth stimulus motion is followed by smooth pursuit eye movements, the forward error is associated with asynchronous processing of retinal and extraretinal information. In the absence of eye movements, no forward displacement is observed with smooth motion. In contrast, implied motion produces a forward error even without eye movements, suggesting that observers extrapolate the next target step when successive target presentations are far apart. Finally, motor responses produce errors that are not observed with perceptual judgments, indicating that the motor system may compensate for neuronal latencies.