Left to right: representational biases for numbers and the effect of visuomotor adaptation

Adaptation to right-shifting prisms improves left neglect for mental number line bisection. This study examined whether adaptation affects the mental number line in normal participants. Thirty-six participants completed a mental number line task before and after adaptation to either: left-shifting prisms, right-shifting prisms or control spectacles that did not shift the visual scene. Participants viewed number triplets (e.g. 16, 36, 55) and determined whether the numerical distance was greater on the left or right side of the inner number. Participants demonstrated a leftward bias (i.e. overestimated the length occupied by numbers located on the left side of the number line) that was consistent with the effect of pseudoneglect. The leftward bias was corrected by a short period of visuomotor adaptation to left-shifting prisms, but remained unaffected by adaptation to right-shifting prisms and control spectacles. The findings demonstrate that a simple visuomotor task alters the representation of space on the mental number line in normal participants.     

Eyeblinking during autokinetic movement observed by a subject living in the up-down inverted visual world

Eyeblinking during autokinetic movement observed by one subject living in the up-down inverted visual world, was investigated. The subject wore frame-spectacles (without prisms) for the first two days and then wore up-down inverting spectacles (with prisms) for the next four days, followed by the resumption of the former frame-spectacles for one day. Eyeblinks during autokinetic movement were measured by using vertical EOG. Analysis showed (1) the occurrence of eyeblinking during autokinetic movement was not influenced by living in the up-down inverted visual world; (2) the frequency of eyeblinking during autokinetic movement significantly decreased with successive days of observation.     

Effects of up-down visual inversion on motor skills

The movement of a hand or fingers and locomotion of the body by a subject wearing prisms which inverted his visual world were investigated. A subject wore frame-spectacles (without prisms) for the first two days and then wore up-down inverting spectacles (with prisms) for the next four days, followed by wearing the former frame-spectacles again for one day. Measurements were made of skill on star-drawing, pegboard tests, and on zigzag-walking and walking up and down stairs. There were no differences on the five measures during acquisition for the four tasks, which suggests smooth progress of prism-adaptation by this man.     

Autokinetic movement and inverted vision

It was considered that inverted vision could influence the condition of the subject's relative framework. The aim of this study was to investigate whether autokinetic movement observed during inverted vision might differ from that in normal vision. One subject wearing inverting spectacles and another one subject in normal vision observed autokinetic movement for five days. The results showed that directional changes increased with the time spent in visual inversion, while in normal vision such tendency was not observed. One speculative interpretation was suggested in terms of subject-related framework.     

Through the inverting glass: first-person observations on spatial vision and imagery

Experience with inverting glasses reveals key factors of spatial vision. Interpretations of the literature based on the metaphor of a “visual image” have raised the question whether visual experience with inverting glasses remains inverted or whether it may turn back to normal after adaptation to the glasses. Here, I report on my experience with left/right inverting glasses and argue that a more fine-grained sensorimotor analysis can resolve the issue. Crucially, inverting glasses introduce a conflict at the very heart of spatial vision. At first, the experience of visual direction grounded in head movements differs from visual experience grounded in eye movements. During adaptation, this difference disappears, and one may learn to see without conflict where objects are located (this took me 123 h of practice). The momentary experience became once again integrated within the larger flow of visual exploration involving head movements, a change of experience that was abrupt and comparable to a Gestalt switch. The resulting experience remains different from normal vision, and I argue that this difference can be understood in sensorimotor terms. I describe how adaptation to inverting glasses is further reflected in mental imagery, supporting the idea that imagery is grounded in sensorimotor engagement with the environment as well.     

Prism Adaptation and Aftereffect: Specifying the Properties of a Procedural Memory System

Prism adaptation, a form of procedural learning, is a phenomenon in which the motor system adapts to new visuospatial coordinates imposed by prisms that displace the visual field. Once the prisms are withdrawn, the degree and strength of the adaptation can be measured by the spatial deviation of the motor actions in the direction opposite to the visual displacement imposed by the prisms, a phenomenon known as aftereffect. This study was designed to define the variables that affect the acquisition and retention of the aftereffect. Subjects were required to throw balls to a target in front of them before, during, and after lateral displacement of the visual field with prismatic spectacles. The diopters of the prisms and the number of throws were varied among different groups of subjects. The results show that the adaptation process is dependent on the number of interactions between the visual and motor system, and not on the time spent wearing the prisms. The results also show that the magnitude of the aftereffect is highly correlated with the magnitude of the adaptation, regardless of the diopters of the prisms or the number of throws. Finally, the results suggest that persistence of the aftereffect depends on the number of throws after the adaptation is complete. On the basis of these results, we propose that the system underlying this kind of learning stores at least two different parameters, the contents (measured as the magnitude of displacement) and the persistence (measured as the number of throws to return to the baseline) of the learned information.     

Eye-position aftereffects of backward head tilt manifested by illusory visual direction

Three experiments showed posttest-minus-pretest shifts in subjective straight-ahead eye position when subjects read for 3, 6, or 9 min with their heads tilted back 20° from upright. These shifts were significant relative to control conditions in which subjects read with their heads upright. All subjects read with the same straight-ahead eye-in-head position. Variability-reducing procedures were developed to provide better measures over Experiments 1, 2. and 3. Explanations in terms of deliberate compensation, head-position asymmetries, eye-position asymmetries, and progressive error were ruled out. It was hypothesized that the shifts were caused by negative aftereffects of compensation for the doll reflex. The doll reflex rotates the eyes down without central registration. causing an upward illusory shift of visual direction similar to what is caused by wedge prisms. Perceptual-motor adaptation to this shift, i.e., doll adaptation, causes an illusory shift in the opposite direction when the head is returned to upright.     

Haptic dominance in form perception: vision versus proprioception.

An experiment placed vision and touch in conflict by the use of a mirror placed perpendicular to a letter display. The mirror induced a discrepancy in direction and form. Subjects touched the embossed tangible letters p, q, b, d, W, and M, while looking at them in a mirror, and were asked to identify the letters. The upright mirror produced a vertical inversion of the letters, and visual inversion of the direction of finger movement. Thus, subjects touched the letter p, but saw themselves touching the letter b in the mirror. There were large individual differences in reliance on the senses. The majority of the subjects depended on touch, and only one showed visual dominance. Others showed a compromise between the senses. The results were consistent with an attentional explanation of intersensory dominance.     

Recalibration of the convergence system.

Adaptation to convergence-altering prism spectacles was studied. The subjects were trained for 8 min with either convergence-increasing or convergence-decreasing prisms. Before and after training they estimated the distance to a binocular dot varying in the stimulus it provided to convergence. Both the preadaptation and postadaptation estimates showed that the reciprocal of estimated target distance is linearly related to convergence. Further there was a consistent change in the direction of adaptation expected from the preadaptation to the postadaptation test. This change was accounted for in terms of a recalibration of the effective absolute convergence level.     

Changes in straight-ahead eye position during adaptation to wedge prisms

If S is instructed to look straight ahead before adapting to laterally displaced vision, he does so without noticeable error. After adapting, however, in response to the same instruction, he may rotate his eyes as much as 8° toward the the displaced visual target. This is the change in judgment of the direction of gaze which Helmholtz identified in 1867 as an important physiological mechanism in adaptation to prisms. It leads to more accurate reaching behavior by causing S to make a visual judgment that the target is closer to straight ahead than it was when he first looked through the prisms. This type of adaptive change (change in judgment of the direction of gaze, oculomotor change) can be measured either by manual judgments (difference between successive “straight ahead” and “visual target” judgments) or by changes in straight-ahead eye position. It may be described as a parametric adjustment in the oculomotor control system, and is closely analogous to the eye movement which subserves the recovery of binocular fusion in prism vergence.     

Prism adaptation changes the subjective proprioceptive localization of the hands

Prism adaptation involves a proprioceptive, a visual and a motor component. As the existing paradigms are not able to distinguish between these three components, the contribution of the proprioceptive component remains unclear. In the current study, a proprioceptive judgement task, in the absence of motor responses, was used to investigate how prism adaptation would specifically influences the felt position of the hands in healthy participants. The task was administered before and after adaptation to left and right displacing prisms using either the left or the right hand during the adaptation procedure. The results appeared to suggest that the prisms induced a drift in the felt position of the hands, although the after‐effect depended on the combination of the pointing hand and the visual deviation induced by prisms. The results are interpreted as in line with the hypothesis of an asymmetrical neural architecture of somatosensory processing. Moreover, the passive proprioception of the hand position revealed different effects of proprioceptive re‐alignment compared to active pointing straight ahead: different mechanisms about how visuo‐proprioceptive discrepancy is resolved were hypothesized.     

Automated vision occlusion-timing instrument for perception–action research

Vision occlusion spectacles are a highly valuable instrument for visual-perception–action research in a variety of disciplines. In sports, occlusion spectacles have enabled invaluable knowledge to be obtained about the superior capability of experts to use visual information to guide actions within in-situ settings. Triggering the spectacles to occlude a performer’s vision at a precise time in an opponent’s action or object flight has been problematic, due to experimenter error in using a manual buttonpress approach. This article describes a new laser curtain wireless trigger for vision occlusion spectacles that is portable and fast in terms of its transmission time. The laser curtain can be positioned in a variety of orientations to accept a motion trigger, such as a cricket bowler’s arm that distorts the lasers, which then activates a wireless signal for the occlusion spectacles to change from transparent to opaque, which occurs in only 8 ms. Results are reported from calculations done in an electronics laboratory, as well as from tests in a performance laboratory with a cricket bowler and a baseball pitcher, which verified this short time delay before vision occlusion. In addition, our results show that occlusion consistently occurred when it was intended—that is, near ball release and during mid-ball-flight. Only 8% of the collected data trials were unusable. The laser curtain improves upon the limitations of existing vision occlusion spectacle triggers, indicating that it is a valuable instrument for perception–action research in a variety of disciplines.     

Adaptive changes of opposite sign in the oculomotor systems of the two eyes

Subjects inspected their feet via base-out prisms for 3 min. Using binocular vision, subsequent reaching without prisms showed significant overestimation of distance. Monocular testing showed a lateral shift in pointing to targets in opposite directions for each eye. This indicates that registered, as opposed to actual, convergence is a factor in near distance perception, and that opposite adaptation occurs within the motor control system for each eye.     

Sensori-motor integration during stance: Time adaptation of control mechanisms on adding or removing vision

Sudden addition or removal of visual information can be particularly critical to balance control. The promptness of adaptation of stance control mechanisms is quantified by the latency at which body oscillation and postural muscle activity vary after a shift in visual condition. In the present study, volunteers stood on a force platform with feet parallel or in tandem. Shifts in visual condition were produced by electronic spectacles. Ground reaction force (center of foot pressure, CoP) and EMG of leg postural muscles were acquired, and latency of CoP and EMG changes estimated by t-tests on the averaged traces. Time-to-reach steady-state was estimated by means of an exponential model. On allowing or occluding vision, decrements and increments in CoP position and oscillation occurred within about 2 s. These were preceded by changes in muscle activity, regardless of visual-shift direction, foot position or front or rear leg in tandem. These time intervals were longer than simple reaction-time responses. The time course of recovery to steady-state was about 3 s, shorter for oscillation than position. The capacity of modifying balance control at very short intervals both during quiet standing and under more critical balance conditions speaks in favor of a necessary coupling between vision, postural reference, and postural muscle activity, and of the swiftness of this sensory reweighing process.     

Visual and proprioceptive adaptation to altered oculomotor adjustments

Adaptation to spectacles that alter in equivalent amounts the accommodation and the convergence with which objects are viewed was produced under two conditions. In one, S alternately pushed away or pulled toward him a screen that exhibited only a single vertical contour while wearing glaaaes that caused decreases in accommodation and convergence equivalent to 1.5 lens diopters. Here kinesthesis for these arm movements provided the only veridical distance cues, A small, but highly significant, adaptation effect was obtained with a teat in which S, before and after the adaptation period, pointed to the location of a test line in the distance dimension. Corresponding tests consisting in size and in depth estimates did not show an adaptation effect. In the other condition of adaptation, S moved objects by hand toward and away from himself while wearing spectacles that increased accommodation and convergence by the equivalent of 1.5 lens diopters. In addition to the altered oculomotor cues, some veridical visual cues for distance such as are caused by perspective were present. This condition yielded changes in size and depth estimates indicative of an adaptation in visual distance perception and a larger effect of adaptation measured by the pointing test. We concluded that the excess of the adaptation effect measured by pointing over that measured by size estimation represents an adaptation in proprioception, as did the pointing effect produced by our first adaptation condition.     

Adaptation to prisms: Do proprioceptive changes mediate adapted behaviour with ballistic arm movements?

In Experiment I subjects pointed repeatedly at a target viewed through laterally displacing prisms and received terminal visual feedback. In one task the pointing movements were slow (proprioceptively controlled), and in the other they were fast (pre-programmed). In both tasks adaptation proceeded at the same rate and to the same level of performance. Following fast pointing with prisms a large amount of arm-body adaptation was found with slow and fast test movements, while following slow pointing with prisms a large amount of arm-body adaptation was found with slow test movements, but only a small amount with fast test movements. The result suggests that adapted behaviour with preprogrammed movements is not mediated by a proprioceptive change. In Experiment II pointing movements were passive. No arm-body adaptation was found with fast test movements, and, contrary to expectation, only a small amount with slow test movements.     

Brightness and image definition of pictures viewed from between the legs

It has been documented that if we see a scene from between our own legs, it appears brighter and more distinct. We determined factors that are critical to these changes and elucidated how they are related to visual disorder that is contingent on bending the head. In Experiment 1, upright scene pictures were viewed with the head inverted. In Experiments 2 and 3, the 180° rotated versions of the same pictures were seen with the head inverted and upright, respectively. In Experiment 4, geometric patterns were seen with the head inverted. In Experiment 5, apparent depth and organization of scene pictures were judged under combinations of retinal-image and head orientations. The first results demonstrated that the scene pictures, when seen with the head inverted, had a 9.8% increase in brightness and a 6.8% increase in image definition as compared to normal upright viewing, but these changes did not arise for geometric patterns. Second, these changes were mainly ascribed to a proprioceptive change of the head. Third, by inverting only the head or the retinal image, visual structure of pictures was disturbed but the visual disorder did not always change brightness and image definition. These findings are discussed.     

Rapid learning by walking observers wearing a reversing or inverting prism

We measured the initial rapid learning of walking observers who wore an up-down inverting or left-right reversing prism. This prism-walking version of the 'mirror-drawing' experiment revealed that the learning curve as a function of the trial number was the same as that typically acquired from a traditional mirror-drawing experiment. We suggest that the initial short-term learning process involved in prism walking is similar to that in mirror drawing and is related to the high-level decision-making process involved in visuo-motor planning of actions with feedback from transformed vision.     

A re-examination of the Stratton effect: Egocentric adaptation to a rotated visual image

The question raised by Stratton, whether a disoriented image can yield upright vision. was explored by exposing Os to a prismatically rotated field. To isolate the problem ofadaptation to altered egocentric orientation, the O’s view was restricted to a horizontal plane during both prism exposure and test. Significant adaptation based on movement-derived information was obtained.     

Changes in the perception of spatial location: A test of potentiation vs. recalibration theory

Two experiments tested recalibration and muscle potentiation theories of adaptation to prismatic displacement of the visual field. Each experiment included a condition in which only recalibration could occur and another condition in which only potentiation was possible. In one experiment, the displacement was simulated on a computer-driven cathode ray tube, and in the other, the displacement was produced by actual prisms. In both experiments, significant adaptation occurred only in the potentiation condition. Implications of this finding for recent criticisms of potentiation theory are discussed.