Human updating of visual motion direction during head rotations

Previous studies have demonstrated that human subjects update the location of visual targets for saccades after head and body movements and in the absence of visual feedback. This phenomenon is known as spatial updating. Here we investigated whether a similar mechanism exists for the perception of motion direction. We recorded eye positions in three dimensions and behavioral responses in seven subjects during a motion task in two different conditions: when the subject's head remained stationary and when subjects rotated their heads around an anteroposterior axis (head tilt). We demonstrated that after head-tilt subjects updated the direction of saccades made in the perceived stimulus direction (direction of motion updating), the amount of updating varied across subjects and stimulus directions, the amount of motion direction updating was highly correlated with the amount of spatial updating during a memory-guided saccade task, subjects updated the stimulus direction during a two-alternative forced-choice direction discrimination task in the absence of saccadic eye movements (perceptual updating), perceptual updating was more accurate than motion direction updating involving saccades, and subjects updated motion direction similarly during active and passive head rotation. These results demonstrate the existence of an updating mechanism for the perception of motion direction in the human brain that operates during active and passive head rotations and that resembles the one of spatial updating. Such a mechanism operates during different tasks involving different motor and perceptual skills (saccade and motion direction discrimination) with different degrees of accuracy.     

Visual vestibular interaction: vestibulo-ocular reflex suppression with head-fixed target fixation

Summary In order to maintain clear vision, the images on the retina must remain reasonably stable. Head movements are generally dealt with successfully by counterrotation of the eyes induced by the combined actions of the vestibulo-ocular reflex (VOR) and the opto-kinetic reflex. We have studied how, in humans, the VOR gain (VORG) is modulated to provide appropriate eye movements in two situations: 1. fixation of a stationary object of the visual space while the head moves. This requires a visuo-vestibulo-ocular reaction to induce eye movements opposite in direction, and equal in velocity to head movements, and 2. fixation of an object moving with the head. Here, the visuo-vestibulo-ocular reaction should be totally suppressed. These two situations were compared to a basic condition in which, to induce pure VOR, the subjects (Ss) in darkness were not allowed a visual target. Eye movements were recorded in seated Ss during constant amplitude sinusoidal and pulse-like passive rotations applied around the vertical axis. Subjects were in total darkness (DARK condition) and performing mental arithmetic. Alternatively, they were provided with a small target, either stationary with respect to earth (earth-fixed target: EFT), or moving with them (chairfixed-target: CFT). The sinusoidal rotation experiment was used as baseline for the ensuing experiments and yielded control data in agreement with the literature. In particular, rotation in the dark showed a VORG of 0.6. With, for example, 0.8 s passive pulse rotations, typical responses in all three visual conditions were rigorously identical during the first 150 to 180 ms. They showed a delay of about 16 ms of the eye behind the head with no significant difference between passive whole-body and passive head-alone rotations. In all conditions, once the eyes had started to move, a rapid increase in eye velocity was observed during 75 to 80 ms, after which, the average VORG was 0.9 ± 0.15. During the following 50 to 100 ms, the gain remained around 0.9 in all three conditions. Beyond 180 ms, the VORG remained around 0.9 in DARK, increased slowly towards 1 or decreased towards zero in the EFT and CFT conditions, respectively. The time-course of these later events suggests that visual tracking mechanisms came into play to reduce retinal slip through smooth pursuit. Sinusoidal rotations, extensively used in VOR studies, do not seem to be a satisfactory stimulus to rapidly and precisely characterize VOR function, particularly in pathological cases. Our data suggest that rapid transient rotations are more appropriate.     

Predictive remapping of visual features precedes saccadic eye movements

The frequent occurrence of saccadic eye movements raises the question of how information is combined across separate glances into a stable, continuous percept. Here I show that visual form processing is altered at both the current fixation position and the location of the saccadic target before the saccade. When human observers prepared to follow a displacement of the stimulus with the eyes, visual form adaptation was transferred from current fixation to the future gaze position. This transfer of adaptation also influenced the perception of test stimuli shown at an intermediate position between fixation and saccadic target. Additionally, I found a presaccadic transfer of adaptation when observers prepared to move their eyes toward a stationary adapting stimulus in peripheral vision. The remapping of visual processing, demonstrated here with form adaptation, may help to explain our impression of a smooth transition, with no temporal delay, of visual perception across glances.     

Vergence effects on the perception of motion-in-depth

When the eyes follow a target that is moving directly towards the head they make a vergence eye movement. Accurate perception of the target's motion requires adequate compensation for the movements of the eyes. The experiments in this paper address the issue of how well the visual system compensates for vergence eye movements when viewing moving targets. We show that there are small but consistent biases across observers: When the eyes follow a target that is moving in depth, it is typically perceived as slower than when the eyes are kept stationary. We also analysed the eye movements that were made by observers. We found that there are considerable differences between observers and between trials, but we did not find evidence that the gains and phase lags of the eye movements were related to psychophysical performance.     

Visual and somatosensory processing in the macaque temporal cortex: the role of ‘expectation’

Summary The somatosensory and visual properties of cells in a polymodal region of temporal cortex were studied in 4 awake behaving macaque monkeys. When stimulated passively and out of sight, cells with tactile responses were found to have very large receptive fields covering most of the body surface and an apparent lack of selectivity for size, shape or texture of the tactile stimulus. These properties are equivalent to those described for the anaesthetized preparation (Bruce et al. 1981). Our study revealed that tactile responses were influenced by the degree to which stimuli could be expected. Tactile stimulation arising from active exploration of novel surfaces produced vigourous neuronal responses but equivalent stimulation of the skin arising when the monkey contacted expected surfaces such as itself or items with which it had become familiar produced no responses. The responses of cells to active or passive tactile stimulation were attenuated when the monkey could see the objects causing the stimulation. For cells responsive to more than one sensory modality, visual and somatosensory responses were associated in a compatible manner. Cells responsive to the onset of touch were selective for the sight of objects moving towards the monkey, whereas cells selective for the offset of touch were responsive to the sight of movements away from the monkey.     

Role of vestibular and neck inputs for the perception of object motion in space

Summary The contribution of vestibular and neck inputs to the perception of visual object motion in space was studied in the absence of a visual background (in the dark) in normal human subjects (Ss). Measures of these contributions were obtained by means of a closed loop nulling procedure; Ss fixed their eyes on a luminous spot (object) and nulled its actual or apparent motion in space during head rotation in space (vestibular stimulus) and/ or trunk rotation relative to the head (neck stimulus) with the help of a joystick. Vestibular and neck contributions were expressed in terms of gain and phase with respect to the visuo-oculomotor/joystick feedback loop which was assumed to have almost ideal transfer characteristics. The stimuli were applied as sinusoidal rotations in the horizontal plane (f= 0.025–0.8 Hz; peak angular displacements, 1–16°). Results: (1) During vestibular stimulation, Ss perceived the object, when kept in fixed alignment with the moving body, as moving in space. However, they underestimated the object motion; the gain was only about 0.7 at 0.2–0.8 Hz and clearly decreased at lower stimulus frequencies, while the phase exhibited a small lead. (2) During pure neck stimulation (trunk rotating relative to the stationary head), the object, when stationary, appeared to move in space counter to the trunk excursion. This neck-contingent object motion illusion was small at 0.2–0.8 Hz, but increased considerably with decreasing frequency, while its phase developed a small lag. (3) Vestibular, neck, and visuo-oculomotor effects summed linearly during combined stimulations. (4) The erroneous vestibular and neck contributions to the object motion perception were complementary to each other, and the perception became about veridical (G1, 0°), when both inputs were combined during head rotation with the trunk stationary. The results are simulated by an extended version of a computer model that previously had been developed to describe vestibular and neck effects on human perception of head motion in space. In the model, the perception of object motion in space is derived from the superposition of three signals, representing object to head, (visuo-oculomotor; head coordinates), head on trunk (neck; trunk coordinates), and trunk in space (vestibular-neck interaction; space coordinates).Supported by Deutsche Forschungsgemeinschaft, SFB 325     

Motion perception during saccadic eye movements

During rapid eye movements, motion of the stationary world is generally not perceived despite displacement of the whole image on the retina. Here we report that during saccades, human observers sensed visual motion of patterns with low spatial frequency. The effect was greatest when the stimulus was spatiotemporally optimal for motion detection by the magnocellular pathway. Adaptation experiments demonstrated dependence of this intrasaccadic motion percept on activation of direction-selective mechanisms. Even two-dimensional complex motion percepts requiring spatial integration of early motion signals were observed during saccades. These results indicate that the magnocellular pathway functions during saccades, and that only spatiotemporal limitations of visual motion perception are important in suppressing awareness of intrasaccadic motion signals.     

Viewing-distance invariance of movement detection

Summary Since visual movement information is often presented in electronic displays or films it is amazing that there is a paucity of research on the influence of viewing distance on motion detection in cinematograms. We report a relatively high degree of detection constancy with changing viewing distance for coherent motion in random-pixel cinematograms. A constant performance irrespective of viewing-distance is called distance-invariance and for motion detection it proves to hold reasonably well for a relatively wide range of viewing distances both for foveal and eccentric vision. The limits of this viewing-distance invariance are explored as a function of screen velocity. Detection performance is quantified by a theshold signal-to-noise-ratio (SNR-) value, S, which is determined as a function of velocity for a range of viewing distances from 53 to 13476 mm for foveal vision and from 60 to 1925 mm at 24° eccentricity on the nasal horizontal meridian of the right eye's retina. The data can be explained, at least qualitatively, by a model in which a spatial-resolution stack has a stack of velocity-tuned motion detectors at every resolution layer. Such a stack-of-stacks model is in line with proposals for contrast-detection stack-models, but it suggests that the usual hypothesis that motion perception is based on the activity of two separate systems, the short-range and the long-range system, might be superfluous. This two-systems distinction was largely based on the different performance found for moving random dot patterns and moving form-defined stimuli. A moving random pixel array viewed at very close range (e.g. 6 cm) presents the subject with relatively large almost square blobs, which are less dissimilar from the phi-stimuli used in classic motion perception studies than random dot stimuli at the usual medium to large viewing distances. It leads to maximum displacement threshold (D_m-) values that are not untypical of the long-range system, but by gradually increasing the viewing-distance and thus decreasing the pixel-size a continuous change is found from typical long-range to typical short-range values of D_m. The two-systems distinction for motion detection appears to refer to the stimulus rather than to the visual system: The motion-detection system might be forced into a local or a global mode of operation by the choice of stimulus.     

Relative phase destabilization during interlimb coordination: the disruptive role of kinesthetic afferences induced by passive movement

The disruption of three patterns of two-limb coordination, involving cyclical flexion-extension movements performed in the same or in different directions, was investigated through application of passive movement to a third limb by the experimenter. The three patterns referred to the homologous, homolateral, and heterolateral (diagonal) limb combinations which were performed in the sagittal plane. The passive movement involved a spatiotemporal trajectory that differed from the movements controlled actively. Even though subjects were instructed to completely ignore the passive limb movement, the findings of experiment 1 demonstrated a moderate to severe destabilization of the two-limb patterns, as revealed by analyses of power spectra, relative phase, cycle duration, and amplitude. This disruption was more pronounced in the homolateral and heterolateral than in the homologous effector combinations, suggesting stronger coupling between homologous than nonhomologous limb pairs. Moreover, passive mobilization affected antiphase (nonisodirectional) movements more than inphase (isodirectional) movements, pointing to the differential stability of these patterns. Experiment 2 focused on homolateral coordination and demonstrated that withdrawal of visual information did not alter the effects induced by passive movement. It was therefore hypothesized that the generation of extra kinesthetic afferences through passive limb motion was primarily responsible for the detriment in interlimb coordination, possibly conflicting with the sensory information accompanying active movement production. In addition, it was demonstrated that the active limbs were more affected by their homologous passive counterpart than by their non-homologous counterpart, favoring the notion of specific interference. The findings are discussed in view of the potential role of kinesthetic afferences in human interlimb coordination, more specifically the preservance of relative phasing through a kinesthetic feedback loop.     

Motor-induced visual motion: hand movements driving visual motion perception

Visual perception can be changed by co-occurring input from other sensory modalities. Here, we explored how self-generated finger movements (left–right or up–down key presses) affect visual motion perception. In Experiment 1, motion perception of a blinking bar was shifted in the direction of co-occurring hand motor movements, indicative of motor-induced visual motion (MIVM). In Experiment 2, moving and static blinking bars were combined with either directional moving or stationary hand motor movements. Results showed that the directional component in the hand movement was crucial for MIVM as stationary motor movements even declined visual motion perception. In Experiment 3, the role of response bias was excluded in a two-alternative forced-choice task that ruled out the effect of response strategies. All three experiments demonstrated that alternating key presses (either horizontally or vertically aligned) induce illusory visual motion and that stationary motor movements (without a vertical or horizontal direction) induce the opposite effect, namely a decline in visual motion (more static) perception.     

Contrast and assimilation in motion perception and smooth pursuit eye movements

The analysis of visual motion serves many different functions ranging from object motion perception to the control of self-motion. The perception of visual motion and the oculomotor tracking of a moving object are known to be closely related and are assumed to be controlled by shared brain areas. We compared perceived velocity and the velocity of smooth pursuit eye movements in human observers in a paradigm that required the segmentation of target object motion from context motion. In each trial, a pursuit target and a visual context were independently perturbed simultaneously to briefly increase or decrease in speed. Observers had to accurately track the target and estimate target speed during the perturbation interval. Here we show that the same motion signals are processed in fundamentally different ways for perception and steady-state smooth pursuit eye movements. For the computation of perceived velocity, motion of the context was subtracted from target motion (motion contrast), whereas pursuit velocity was determined by the motion average (motion assimilation). We conclude that the human motion system uses these computations to optimally accomplish different functions: image segmentation for object motion perception and velocity estimation for the control of smooth pursuit eye movements.     

Active linear head motion improves dynamic visual acuity in pursuing a high-speed moving object

We usually move both our eyes and our head when pursuing a high-speed moving object. However, the vestibulo-ocular reflex (VOR), evoked by head motion, seems to disturb smooth pursuit eye movement because the VOR stabilizes the gaze against head motion. To determine whether head motion is advantageous for pursuing a high-speed moving object, we examined dynamic visual acuity (DVA) for a high-speed (80°/s) rightward moving object with and without active linear rightward head motion (HM) at a maximum of 50 cm/s in nine healthy subjects. Furthermore, we analyzed eye and head movements to investigate the contribution of linear VOR (LVOR) and smooth eye movement under these conditions. In most subjects, active linear head motion improved DVA for a high-speed moving object. Subjects with higher DVA scores under HM had robust rightward gaze (eye + head) velocities (>60 cm/s), i.e., rightward smooth eye movements (>10°/s). With the head stationary (HS), faster smooth eye movements (>40°/s) were generated when the subjects pursued a high-speed moving object. They also showed anticipatory smooth eye movements under conditions HM and HS. However, the level of suppression of their LVOR abilities was equal to that of the others. These results suggest that the ability to generate anticipatory smooth pursuit eye movements for following a high-speed moving object against the LVOR is a determining factor for improvement of DVA under HM.     

Adaptive modification of vestibularly perceived rotation

Summary Results from Bloomberg et al. (1991) led to the hypothesis that saccades which accompany the darktested vestibulo-ocular reflex (VOR) tend to move the eyes towards a vestibularly derived percept of an intended oculomotor goal: also that this is so even when that percept has been adaptively modified by suitably prolonged visual-vestibular conflict. The present experiments investigate these implications by comparing the combined VOR+saccade performance with a presumed motor readout of the normal and adaptively modified vestibular percept. The methods employed were similar to those of an earlier study Bloomberg et al. (1988) in which it was found that after cessation of a. brief passive whole body rotation in the dark, a previously seen earth-fixed target can be accurately located by saccadic eye movements based on a vestibular memory of the preceding head rotation; the so-called Vestibular Memory-Contingent Saccade (VMCS) paradigm. The result showed that the vestibular perceptual response, as measured after rotation by means of the VMCS paradigm was on average indistinguishable from the combined VOR + saccade response measured during rotation. Furthermore, this was so in both the normal and adapted states. We conclude that these findings substantiate the above hypothesis. The results incidentally reaffirm the adaptive modifiability of vestibular perception, emphasing the need for active maintenance of its proper calibration according to behavioural context.     

Conjugate and disjunctive optokinetic eye movements in the rabbit,evoked by rotatory and translatory motion

Summary Horizontal movements of both eyes of rabbits were recorded simultaneously, using a scleral search coil system. Several types of motion of the environment were produced: a) a circular striped drum rotating around the animal (true rotation), b) flat striped patterns moving in parasagittal planes, one forward, the other backward (pseudorotation), c) flat patterns moving both either backward or forward (tunnelmotion).True rotation and pseudorotation evoked a regular optokinetic nystagmus (OKN). Systematic asymmetries in the OKN of the two eyes were found. As was already known, each eye apart is much more sensitive to forward than to backward motion. The eye that sees forward motion proves to have a larger slow phase velocity and amplitude of OKN and therefore a better gain than the crossed eye, which is to a great dealdriven by the other eye. This asymmetry is more clearly exposed by covering one eye; the seeing eye is then the leading one in both directions.Tunnelmotion elicited vergence movements in all rabbits. Bilateral forward motion induced convergence, backward motion divergence. The range between extreme convergence and divergence varied from 7–23°. Occasionally, a regular vergence nystagmus was elicited by forward motion; in this case some of the fast phases of the two eyes were oppositely directed.It is concluded that disjunctive eye movements can be induced in the rabbit by certain visual stimuli. It is doubtful whether vergence movements are ever normally used by the rabbit for binocular vision of objects at varying distances. A role in individual drift-correction for each eye appears more plausible.     

Sensory versus motor loci for integration of multiple motion signals in smooth pursuit eye movements and human motion perception

We have investigated how visual motion signals are integrated for smooth pursuit eye movements by measuring the initiation of pursuit in monkeys for pairs of moving stimuli of the same or differing luminance. The initiation of pursuit for pairs of stimuli of the same luminance could be accounted for as a vector average of the responses to the two stimuli singly. When stimuli comprised two superimposed patches of moving dot textures, the brighter stimulus suppressed the inputs from the dimmer stimulus, so that the initiation of pursuit became winner-take-all when the luminance ratio of the two stimuli was 8 or greater. The dominance of the brighter stimulus could be not attributed to either the latency difference or the ratio of the eye accelerations for the bright and dim stimuli presented singly. When stimuli comprised either spot targets or two patches of dots moving across separate locations in the visual field, the brighter stimulus had a much weaker suppressive influence; the initiation of pursuit could be accounted for by nearly equal vector averaging of the responses to the two stimuli singly. The suppressive effects of the brighter stimulus also appeared in human perceptual judgments, but again only for superimposed stimuli. We conclude that one locus of the interaction of two moving visual stimuli is shared by perception and action and resides in local inhibitory connections in the visual cortex. A second locus resides deeper in sensory-motor processing and may be more closely related to action selection than to stimulus selection.     

Eye movements cannot explain vibration-induced visual motion and motion aftereffect

Eye movements are thought to account for a number of visual motion illusions involving stationary objects presented against a featureless background or apparent motion of the whole visual field. We tested two different versions of the eye movement account: (a) the retinal slip explanation and (b) the nystagmus-suppression explanation, in particular their ability to account for visual motion experienced during vibration of the neck muscles, and for the visual motion aftereffect following vibration. We vibrated the neck (ventral sternocleidomastoid muscles, bilaterally, or right dorsal muscles) and measured eye movements in conjunction with perceived illusory displacement of an LED presented in complete darkness (N=10). To test the retinal-slip explanation, we compared the direction of slow eye movements to the direction of illusory motion of the visual target. To test the suppression explanation, we estimated the direction of suppressed slow-phase eye movements and compared it to the direction of illusory motion. Two main findings show that neither actual nor suppressed eye movements cause the illusory motion and motion aftereffect. Firstly, eye movements do not reverse direction when the illusory motion reverses after vibration stops. Secondly, there are large individual differences with regards to the direction of eye movements in observers who all experience a similar visual illusion. We conclude that, rather than eye movements, a more global spatial constancy mechanism that takes into account head movement is responsible for the illusion. The results also argue against the notion of a single central signal that determines both perceptual experience and oculomotor behaviour.     

Neural correlates of reafference: evoked brain activity during motion perception and saccadic eye movements

The ability to perceive a stable visual environment despite eye movements and the resulting displacement of the retinal image is a striking feature of visual perception. In order to study the brain mechanism related to this phenomenon, an EEG was recorded from 30 electrodes spaced over the occipital, temporal and parietal brain areas while stationary or moving visual stimuli with velocities between 178 degrees/s and 533 degrees/s were presented. The visual stimuli were presented both during saccadic eye movements and with stationary eyes. Stimulus-related potentials were measured, and the effects of absolute and relative stimulus velocity were analyzed. Healthy adults participated in the experiments. In all 36 subjects and experimental conditions, four potential components were found with mean latencies of about 70, 140, 220 and 380 ms. The latency of the two largest components between 100 and 240 ms decreased while field strength increased with higher absolute stimulus velocity for both stationary and moving eyes, whereas relative stimulus velocity had no effect on amplitude, latency and topography of the visual evoked potential (VEP) components. If the visual system uses retinal motion information only, we would expect a dependence upon relative velocity. Since field strength and latency of the components were independent of eye movements but dependent upon absolute stimulus velocity, the visual cortex must use extraretinal information to extract stimulus velocity. This was confirmed by the fact that significant topographic changes were observed when brain activity evoked during saccades and with stationary eyes was compared. In agreement with the reafference principle, the findings indicate that the same absolute visual stimulus activates different neuronal elements during saccades than during fixation.     

Translational head movements of pigeons in response to a rotating pattern: characteristics and tool to analyse mechanisms underlying detection of rotational and translational optical flow

Summary Pigeons freely standing in the centre of a two-dimensionally textured cylinder not only rotate but also laterally translate their head in response to the pattern sinusoidally oscillating or unidirectionally rotating around their vertical axis. The translational head movement dominates the response at high oscillation frequencies, whereas in a unidirectionally rotating drum head translation declines at about the same rate as the rotational response increases. It is suggested that this is a consequence of charging the velocity storage in the vestibulo-ocular system. Similar to the rotational head movement (opto-collic reflex), the translational head movement is elicited via a wide-field motion sensitive system. The underlying mechanism can be described as vector integration of movement vectors tangential to the pattern rotation. Stimulation of the frontal visual field elicits largest translational responses while rotational responses can be elicited equally well from any azimuthal position of a moving pattern. Experiments where most of the pattern is occluded by a screen and the pigeon is allowed to view the stimulus through one or two windows demonstrate a short-range inhibition and longrange excitation between movement detectors that feed into the rotational system. Furthermore, the results obtained from such types of experiments suggest that the rotational system inhibits the translational system. These mechanisms may help the pigeon to decompose image flow into its translational and rotational components. Because of their translational response to a rotational stimulus, it is concluded, however, that pigeons either generally cannot perfectly perform the task or they need further visual information, like differential image motion, that was not available to them in the paradigms.     

Neural basis of stable perception of an ambiguous apparent motion stimulus

Although it has been shown that an alternative dominant percept induced by an ambiguous visual scene has neural correlates in various cortical areas, it is not known how such a dominant percept is maintained until it switches to another. We measured the primary visual response to the two-frame bistable apparent motion stimulus (stroboscopic alternative motion) when observers continuously perceived one motion and compared this with the response for another motion using magnetoencephalography. We observed a response component at around 160 ms after the frame change, the amplitude of which depended on the perceived motion. In contrast, brain responses to less ambiguous and physically unambiguous motions in both the horizontal and vertical directions did not evoke such a component. The differential response evoked by the bistable apparent motion is therefore distinct from directionally-selective visual responses. The results indicate the existence of neural activity related to establish and maintain one dominant percept, the magnitude of which is related to the ambiguity of the stimulus. This is in the line with the currently proposed idea that dominant percept is established in the distributed cortical areas including the early visual areas. Further, the existence of the neural activity induced only by the ambiguous image suggests that the competitive neural activities for the two possible percepts exist even when one dominant image is continuously perceived.     

Inluence of eye motion on adaptive modifications of the vestibulo-ocular reflex in the rat

While sustained retinal slip is assumed to be the basic conditioning stimulus in adaptive modifications of the vestibulo-ocular reflex (VOR) gain, several observations suggest that eye motion-related signals might also be involved. We oscillated pigmented rats over periods of 20 min around the vertical axis, at 0.3 Hz and 20°/s peak velocity, in different retinal slip and/or eye motion conditions in order to modify their VOR gain. The positions of both eyes were recorded by means of a phase-detection coil system with the head restrained. The main findings came from the comparison of two basic conditions — including their respective controls — in which one or both eyes were reversibly immobilised by threads sutured to the eyes. In the first condition the animals were rotated in the light with one eye immobilised and the other eye free to move but covered. Rotation in the light in this open-loop condition immediately elicited high-gain compensatory eye movements of the non-impeded, covered eye. At the end of this training procedure, the VOR gain increased by 42.3%. In the second condition, both eyes were immobilised and one eye was covered. The result was an increase in the VOR gain of 26.3%. These two conditions were similar as to the visuo-vestibular drive during the exposure, but different as to the resulting — and allowed — eye motion, showing that the condition where the larger eye movements occurred yielded the larger VOR gain change. Our data support the idea proposed by Collewijn and Grootendorst (1979, p. 779) and Collewijn (1981, p. 146) that [retinal] slip and eye movements seem to be relevant signals for the adaptation of the rabbit's visuo-vestibular oculomotor reflexes. Our data also suggest that sensory information related to eye movements, more likely than efference copy, is the coding signal for eye movement which combines with the retinal slip signal to generate adaptive changes of the VOR.