Reduced felt arm sensation effects on visual adaptation

Proprioception is often considered to be critically involved in producing adaptation to a prism-induced visual displacement. The present study focused on reduction of proprioceptive feedback during prism exposure by means of hypnotically induced anesthesia in the adapting arm. In addition, intermanual transfer was considered. Results showed adaptation occurring in situations where S could feel arm sensations while viewing arm movement during a prism exposure. However, if the adapting arm was hypnotically anesthetized while still remaining mobile, adaptation did not occur. No intermanual transfer was found between the adapted arm and the unadapted arm.     

Counteradaptation after exposure to displaced visual direction

Counteradaptation, previously demonstrated in connection with adaptation in distance perception, was obtained after exposure to displaced visual direction. When S adapted to a laterally displacing wedge prism by walking during the exposure period, there was not only a change in the perceived visual direction, but also a change m the proprioceptively perceived walking direction. When S adapts to lateral displacement of the visual direction by looking at his stationary or his moving arm, visual adaptation is obtained in the latter, but not in the former, case (Held & Hein, 1958). We obtained a change in the proprioceptively perceived position of the arm when it was stationary during the exposure period, a condition which had not yielded visual adaptation, and a much smaller, not significant, change in the felt position in the case of the actively moved arm. In the present experiments, changes in proprioceptively perceived direction or position amounted to counteradaptation.     

Visuomotor coordination and intermanual transfer for a proprioceptive reaching task

Two experiments were conducted to determine the role of head constraint, whether present or absent and arm exposure type (terminal or continuous) on the production of intermanual transfer to two types of visual distortion. Experiment 1 investigated intermanual transfer to binocular, lateral prism displacement where the prism base orientation for both eyes was in the same direction. Experiment 2 determined whether intermanual transfer could be produced to squint prism viewing where the prism base orientation for each eye was in an opposite direction (base-out prisms). In both experiments transfer was produced when either head movement during prism exposure was unconstrained or when a terminal arm exposure was employed. Maximal transfer was produced when both of these conditions were employed.     

The role of acceleration information in prism adaptation

Two experiments were performed in which the acceleration component of limb movement information during prism exposure was manipulated, by controlling the trajectory and visibility of arm movement. When limb movements were confined to a lateral motion on a linear track, adaptation was evident when arm movement reversal at the end of the trajectory could be viewed (nonoccluded arm-movement reversal conditions). No adaptation occurred in the occluded arm-movement reversal condition. When movements were made on a curved track, adaptation was evident in both the nonoccluded and the occluded arm-movement reversal conditions. The results indicate that the acceleration component of reafferent stimulation may be critical in prism adaptation when no error information is available.     

Factors affecting proprioceptive adaptation to prismatic displacement

Two prism displacement experiments were conducted to determine the effects of reducing proprioceptive feedback on resultant adaptation magnitude. In Experiment 1, proprioceptive reduction was produced by requesting subjects to employ passive Ivs. active) and/or fast- Ivs. slow-) paced arm movement during prism exposure. When both of these conditions were present, a significant reduction in the magnitude of proprioceptive adaptation and a significant increase in the magnitude of visual adaptation were produced. In Experiment 2, hypnotic anesthesia was employed to reduce felt sensation in an adapting limb during a prism displacement situation. This manipulation reduced proprioceptive adaptation to a nonsignificant level. The combined results of the two experiments reveal several conditions that can serve to reduce proprioceptive adaptation during prism displacement.     

Effects of situational cues on prism-induced aftereffects

A test was made of the hypothesis that external stimuli present during exposure to lateral displacement of the visual field can serve as situational cues whose presence or absence will influence the magnitude of aftereffects manifested subsequent to adaptation resulting from the exposure. The results indicated that the relative aftereffects were significantly greater when thenondisplacing goggles were worn during the periods in which aftereffect measurements were taken than was the case when they were removed during these test periods. The finding that manipulation of certain cues, i.e., the restriction of the visual field, weight, etc., of the goggles, associated with the adaptation period can in part determine the size of observed aftereffects provides evidence in support of the notion that aftereffects can be conditioned to precisely given constellations of stimuli In addition, the need for caution in conceptualizing aftereffects as simply the persistence of adaptive shifts once visual displacement has been terminated is suggested.     

Arm-body adaptation with passive arm movements

Two experiments investigated the aftereffects of pointing with passive movements during exposure to 15-deg laterally displacing wedge pnsms. Experiment 1 compared exposure with passive and active supported movements when the aftereffects were measured with the arm still in the passive movement device. Following passive exposure and active supported exposure, 5.6 and 7.9 deg, respectively, of arm-body adaptation were measured. In Experiment 2, the passive and active supported exposure tasks were compared with a third task in which similar movements were made with the arm fully supported by the muscles. Aftereffects were measured with active test movements. The amount of arm-body adaptation measured following passive exposure was decreased to 2.8 deg, and following active supported exposure it was decreased to 2.8 deg, while following exposure with normal active movements, 5.3 deg of arm-body adaptation was found. The results suggest that when the arm remains outstretched during prism exposure, adaptation is specific to this extended posture.     

Movement and illumination factors in adaptation to prismatic viewing

While wearing laterally displacing prisms, Ss were required to align a spot of light to the phenomenal straightahead. These measurements were obtained at the beginning and at the end of an exposure to prismatic displacement. In addition, Ss either actively controlled movement of the spot of light, or movement was manipulated by E under the direction of the S. Aftereffects were determined by having S position the spot of light with normal vision at the beginning of the experiment and after each measurement obtained under prism viewing. Ss in the darkened room condition who were required to align the spot of light actively showed a significant aftereffect in the direction of prismatic displacement both at the beginning and at the end of the exposure period. No difference in the degree of adaptation was found between those measurements at the beginning and at the end of the exposure period. No significant aftereffects were found when the room was illuminated during prism exposure or when E controlled movement of the light source.     

Discriminative conditioning of prism adaptation

Two experiments were used to demonstrate that adaptation to ll-deg prism displacement can be conditioned to the stimuli associated with the goggles in which the prisms are housed. In Experiment 1 it was found that repeated alternation between a series of target-pointing responses while wearing prism goggles and a series of responses without prism goggles led to larger adaptive shift when S was tested with nondisplacing goggles than when tested without goggles. The results of Experiment 2 indicated that the adaptation revealed in the first experiment was primarily proprioceptive, rather than visual. Surprisingly, most Ss reported greater difficulty during the exposure period in overcoming the negative aftereffect than they did the prism-induced error.     

The relationship between cognitive,motor-kinesthetic,and oculomotor adaptation

The literature concerning adaptation to prism indicates that several adaptive mechanisms may be important. The particular mechanism or mechanisms involved depends (at least in part) upon the type of adaptive exposure. In the present study. three adaptive mechanisms (cognitive. oculomotor, and motor-kinesthetic) were investigated. Ss were asked to point in the dark at an illuminated target. The target was seen displaced from its veridical position due to a wedge prism placed before S’s right eye. The left eye was occluded. Ss then viewed their visual target pointing errors through the displacing prism without seeing any part of their bodies. One group of Ss was instructed to ignore these prism-induced errors and to continue pointing at the target’s visual position. A second group of Ss was instructed to compensate fully for their errors and to at tempt to eliminate them on all future trials. For the latter group errors were completely eliminated, while for Ss instructed to ignore their errors, relatively small improvement in visual target settings occurred. This improvement was called cognitive adaptation, since it depended on the S’s conscious control. In addition. for both conditions. evidence was found that allowing Ss to view their prism-induced pointing errors resulted in some form of motor-kinesthetic adaptation. This adaptation was hypothesized to represent a change in the judged position of the pointing hand relative to its felt position. It was concluded that this motor-kinesthetic adaptation was dependent, in part, upon cognitive information concerning the effects of the prism and that it serves to reduce conflict between cognitive and visual cues, i.e., between what S believes and what he sees.     

Prismatic displacement of vision induces transient changes in the timing of eye-hand coordination

Eye-hand coordination was investigated during a task of finger pointing toward visual targets viewed through wedge prisms. Hand and eye latencies and movement times were identical during the control condition and at the end of prism exposure. A temporal reorganization of eye and hand movements was observed during the course of adaptation. During the earlier stage of prism exposure, the time gap between the end of the eye saccade and the onset of hand movement was increased from a control time of 23 to 68 msec. This suggests that a time-consuming process occurred during the early prism-exposure period. The evolution of this time gap was correlated with the evolution of pointing errors during the early stage of prism exposure, in such a way that both measures increased at the onset of prism exposure and decreased almost back to control values within about 10 trials. However, spatial error was not entirely corrected, even late in prism exposure when the temporal organization of eye and hand had returned to baseline. These data suggest that two different adaptive mechanisms were at work: a rather short-term mechanism, involved in normal coordination of spatially aligned eye and hand systems, and a long-term mechanism, responsible for remapping spatially misaligned systems. The former mechanism can be strategically employed to quickly optimize accuracy in a situation involving misalignment, but completely adaptive behavior must await the slower-acting latter mechanism to achieve longterm spatial alignment.     

An examination of the relationship between visual capture and prism adaptation

The phenomena of prismatically induced “visual capture” and adaptation of the hand were compared. In Experiment 1, it was demonstrated that when the subject’s hand was transported for him by the experimenter (passive movement) immediately preceding the measure of visual capture, the magnitude of the immediate shift in felt limb position (visual capture) was enhanced relative to when the subject moved the hand himself (active movement). In Experiment 2, where the dependent measure was adaptation of the prism-exposed hand, the opposite effect was produced by the active/passive manipulation. It appears, then, that different processes operate to produce visual capture and adaptation. It was speculated that visual capture represents an immediate weighting of visual over proprioceptive input as a result of the greater precision of vision and/or the subject’s tendency to direct his attention more heavily to this modality. In contrast, prism adaptation is probably a recalibration of felt limb position in the direction of vision, induced by the presence of a registered discordance between visual and proprioceptive inputs.     

Properties of intermodal transfer after dual visuo- and auditory-motor adaptation

Previous work documented that sensorimotor adaptation transfers between sensory modalities: When subjects adapt with one arm to a visuomotor distortion while responding to visual targets, they also appear to be adapted when they are subsequently tested with auditory targets. Vice versa, when they adapt to an auditory-motor distortion while pointing to auditory targets, they appear to be adapted when they are subsequently tested with visual targets. Therefore, it was concluded that visuomotor as well as auditory-motor adaptation use the same adaptation mechanism. Furthermore, it has been proposed that sensory information from the trained modality is weighted larger than sensory information from an untrained one, because transfer between sensory modalities is incomplete. The present study tested these hypotheses for dual arm adaptation. One arm adapted to an auditory-motor distortion and the other either to an opposite directed auditory-motor or visuomotor distortion. We found that both arms adapted significantly. However, compared to reference data on single arm adaptation, adaptation in the dominant arm was reduced indicating interference from the non-dominant to the dominant arm. We further found that arm-specific aftereffects of adaptation, which reflect recalibration of sensorimotor transformation rules, were stronger or equally strong when targets were presented in the previously adapted compared to the non-adapted sensory modality, even when one arm adapted visually and the other auditorily. The findings are discussed with respect to a recently published schematic model on sensorimotor adaptation.     

Adaptation to visual and proprioceptive rearrangement: Origin of the differential effectiveness of active and passive movements

In Experiment 1, subjects exposed to a discordance between the visual and ”proprioceptive” locations of external targets were found to exhibit aftereffects when later pointing without sight of their hands at visual targets. Aftereffects occur both when the discordance is introduced in the traditional fashion by displacing the visual locations of targets and when the proprioceptive locations of targets are displaced. These observations indicate that there is nothing unique about the visual rearrangement paradigm—the crucial factor determining whether adaptation will be elicited is the presence of a discordance in the positional information being conveyed over two different sensory modalities. In a second experiment, the effectiveness of active and passive movements in eliciting adaptation was studied using an experimental paradigm in which subjects were exposed to a systematic discordance between the visual and proprioceptive locations of external targets without ever being permitted sight of their hands; a superiority of active movements was observed, just as is usually found in visual rearrangement experiments in which sight of the hand is permitted. Evidence is presented that the failure of passive movements to elicit adaptation is related to a deterioration in accuracy of position sense information during passive limb movement.     

Interlimb differences in visuomotor and dynamic adaptation during targeted reaching in children

While a number of studies have focused on movement (a)symmetries between the arms in adults, less is known about movement asymmetries in typically developing children. The goal of this study was to examine interlimb differences in children when adapting to novel visuomotor and dynamic conditions while performing a center-out reaching task. We tested 13 right-handed children aged 9–11 years old. Prior to movement, one of eight targets arranged radially around the start position was randomly displayed. Movements were made either with the right (dominant) arm or the left (nondominant) arm. The children participated in two experiments separated by at least one week. In one experiment, subjects were exposed to a rotated visual display (30° about the start circle); and in the other, a 1 kg mass (attached eccentrically to the forearm axis). Each experiment consisted of three blocks: pre-exposure, exposure and post-exposure. Three measures of task performance were calculated from hand trajectory data: hand-path deviation from the straight target line, direction error at peak velocity and final position error. Results showed that during visuomotor adaptation, no interlimb differences were observed for any of the three measures. During dynamic adaptation, however, a significant difference between the arms was observed at the first cycle during dynamic adaptation. With regard to the aftereffects observed during the post-exposure block, direction error data indicate considerably large aftereffects for both arms during visuomotor adaptation; and there was a significant difference between the arms, resulting in substantially larger aftereffects for the right arm. Similarly, dynamic adaptation results also showed a significant difference between the arms; and post hoc analyses indicated that aftereffects were present only for the right arm. Collectively, these findings indicate that the dominant arm advantage for developing an internal model associated with a novel visuomotor or dynamic transform, as previously shown in young adults, may already be apparent at 9 to 11-year old children.     

Calibration and Alignment are Separable: Evidence From Prism Adaptation

In 2 prism adaptation experiments, the authors investigated the effects of limb starting position visibility (visible or not visible) and visual feedback availability (early or late in target pointing movements). Thirty-two students participated in Experiment 1 and 24 students participated in Experiment 2. Independent of visual feedback availability, constant error was larger and variable error was smaller for target pointing when limb starting position was visible during prism exposure. Independent of limb starting position visibility, aftereffects of prism exposure were determined by visual feedback availability. Those results support the hypothesis that calibration is determined by limb starting position visibility, whereas alignment is determined separately by visual feedback availability.     

Is prism adaptation "for" growth?

The assumption that prism adaptation mechanisms evolved for developmental plasticity was questioned by analyzing natural transformations (magnification, rotation, displacement) of the arm and shoulder. Accommodating ordinary movement was found to be a closer match to prisms than transformations caused by growth. In addition, overlap between equations of movement and growth may point to a distal function of adaptation that is very general.     

Adaptive Mechanisms in Perceptual-Motor Coordination

Aftereffect measures of visual shift and proprioceptive shift were obtained for prism exposure conditions in which, at the end of a sagittal pointing movement, most of the arm was visible (concurrent exposure) or only the first finger joint was visible (terminal exposure). Intermediate exposure conditions permitted view of the hand or the first two finger joints. Under the concurrent exposure condition, proprioceptive shift was greater than visual shift but, as view of the pointing hand decreased, the relative magnitude of the two components gradually reversed so that, under the terminal exposure condition, visual shift was greater than proprioceptive shift. These results are discussed in terms of a model of perceptual-motor organization (Redding, Clark, & Wallace, 1985) in which the direction of coordinative linkage between eye-head and hand-head systems determines the locus of discordance and adaptive recalibration.     

Adaptive mechanisms in perceptual-motor coordination: components of prism adaptation

Aftereffect measures of visual shift and proprioceptive shift were obtained for prism exposure conditions in which, at the end of a sagittal pointing movement, most of the arm was visible (concurrent exposure) or only the first finger joint was visible (terminal exposure). Intermediate exposure conditions permitted view of the hand or the first two finger joints. Under the concurrent exposure condition, proprioceptive shift was greater than visual shift but, as view of the pointing hand decreased, the relative magnitude of the two components gradually reversed so that, under the terminal exposure condition, visual shift was greater than proprioceptive shift. These results are discussed in terms of a model of perceptual-motor organization (Redding, Clark, & Wallace, 1985) in which the direction of coordinative linkage between eye-head and hand-head systems determines the locus of discordance and adaptive recalibration.     

Additivity in adaptation to optical tilt

Tests of proprioceptive adaptation (head-hand), visual adaptation (eye-head), and both components (eye-hand) were made during 15-min exposure to 20 degrees tilt in two experiments. In both experiments, subjects alternated exposures in which they explored hallways (hall) or viewed their active hand (hand), but in Experiment 2 subjects received two exposures to each condition, while in Experiment 1 only one exposure was given. Hall exposure produced greater visual change, and hand exposure produced greater proprioceptive change; but in both conditions, when order of conditions was controlled, the sum of performance on visual and proprioceptive tests was not statistically different from performance on the common test. In Experiment 2, adaptive components appeared to be inversely related, both within and between exposure conditions, thus providing some evidence of a reciprocal relationship, but a reliable negative correlation between components was not found. Finally, adaptation increased over alternation-repetition of exposure tasks in the second experiment, even though adaptation appeared limited within any given exposure. Results are interpreted in terms of the linear model, and the possible role of attentional factors in processing sensory inconsistencies is discussed.