Sources of “overadditivity” in prism adaptation

In two experiments, tests of visual shift (VS), proprioceptive shift (PS), and negative aftereffect (NA)were made following 15-min exposure to 20-D (base-right) displacement. In Experiment 1, subjects engaged in saggital pointing (hand exposure) at single or multiple (three) exposure targets, while in Experiment 2, subjects experienced hand exposure or hallway exploration (hall exposure) factorially combined with single or multiple (three) NA test targets. In both experiments, additivity (VS+PS = NA) appeared for multiple target conditions while single target conditions produced “overadditivity” (VS+ PS >NA). This additivity effect for target conditions did not interact with exposure conditions in Experiment 2, although VS was greater in hall exposure and PS was greater in hand exposure. The presence of additivity with multiple targets was supported by a higher correlation between the NA test and each component test with multiple targets in both experiments. These results are interpreted as indicating two causes of overadditivity: specific motor response learning with single-exposure targets and association of a single NA test target with a cognitive shift in egocentric straight-ahead.     

Effects of homogeneous and variable exposure on magnitude of adaptation to optical tilt

Repeated exposure to hallway exploration, alternated with periods of either watching the active hand or exploring a different set of hallways, maintains increasing visual adaptation beyond the point in time at which previous studies using homogeneous exposure have found such visual shift (VS) to be asymptotic. Experiment 1 established that this alternation-repetition effect does not depend on an actual change in task (hall to hand) but also occurs when the task context alone is changed (hall to hall). Experiment 2 compared variable (hall-to-hall) exposure with homogeneous (hall) exposure, showing that variable exposure removes the usual limit on adaptation. In both experiments, proprioceptive shift (PS) and total negative aftereffect (NA) both tended to be less than VS, producing substantial overadditivity (i.e., VS + PS greater than NA). General requirements for an attentional explanation of the alternation-repetition effect are outlined, and possible explanations of overadditivity consistent with the linear model are discussed.     

Components of displacement adaptation in acquisition and decay as a function of hand and hall exposure

Tests of proprioceptive shift (PS), visual shift (VS), and negative aftereffect (NA) were made during 25-min exposure to 20-D displacement and during a subsequent 30-min dark decay period in two separate experiments. Different groups of subjects explored hallways or viewed their active hand during exposure. VS was greatest in hall exposure, while PS was greatest in hand exposure. Larger VS occurred in the second experiment, where test procedures were modified to minimize a tendency to center the target within the momentary or remembered field of view. Substantial and possibly complete VS decay occurred when the initial level of adaptation was high, but although PS decay was substantial, it was not complete. In all conditions, the sum of VS and PS numerically exceeded the NA, and this difference tended to be largest and significant in the hall exposure. Implications of this effect for the two-component additivity hypothesis are discussed.     

Prism adaptation in left-handers

Two experiments with left-handers examined the features of prism adaptation established by previous research with right-handers. Regardless of handedness, (1) rapid adaptation occurs in exposure pointing with developing error in the opposite direction after target achievement, especially with early visual feedback in target pointing; (2) proprioceptive or visual aftereffects are larger, depending on whether visual feedback is available early or late, respectively, in target pointing; (3) the sum of these aftereffects is equal to the total aftereffect for the eye-hand coordination loop; (4) intermanual transfer of visual aftereffects occurs only for the dominant hand; and (5) visual aftereffects are larger in left space when the dominant hand is exposed to leftward displacement. A notable handedness difference is that, while transfer of proprioceptive aftereffects only occurs to the nondominant hand in right-handers, transfer occurs in both directions for left-handers, but regardless of handedness, such transfer only occurs when the exposed hand is tested first after exposure. A discussion then focuses on the implications of these data for a theory of handedness.     

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.     

Intermanual transfer of prism adaptation

The authors measured intermanual transfer in participants (N = 48) whose exposed or unexposed right or left hand was tested 1st after participants experienced prismatic displacement. Test order did not affect either participants' performance during prismatic exposure or the usual aftereffects, but transfer occurred only when the authors tested the exposed right hand 1st. Transfer did not occur, and proprioceptive shift for the exposed left limb decreased when the authors tested the unexposed right limb 1st. The present results suggest that transfer occurs during testing for aftereffects of prism exposure, but not during prism exposure itself, as researchers have previously assumed. Results are consistent with those of previous research that has shown that limb control is lateralized in opposite hemispheres and that the left hemisphere contains a spatial map only for the right limb.     

Effects on Prism Adaptation of Duration and Timing of Visual Feedback During Pointing

In two experiments, we investigated the effects of duration of visual feedback of the pointing limb and the time (early to late) in the movement when the limb first becomes visible (timing of visual feedback). Timing, rather than duration of visual feedback, proved to have the greater effect on the relative magnitude of visual and proprioceptive adaptation. Visual adaptation increased smoothly with feedback delay, but corresponding decreases in proprioceptive adaptation underwent an additional sharp change when feedback was delayed until about three-fourths of the way to the terminal limb position. These results are consistent with the idea that visual and proprioceptive adaptation are mediated by exclusive processes. Change in the limb position sense (i.e., proprioceptive adaptation) may be produced by visual guidance of the pointing limb, and view of the limb early in the pointing movement seems to be critical for such visual guidance. The limb may be ballistically “released“ as it nears the terminal position, and, thereafter, any opportunity for visual guidance (i.e., view of the limb) is not effective. On the other hand, change in the eye position sense (i.e., visual adaptation) may be mediated by proprioceptive guidance of the eye; the eyes may track the imaged position of the nonvisible limb. Such proprioceptive guidance seems to be solely a function of the distance moved before the limb becomes visible.     

Prism adaptation in alternately exposed hands

We assessed intermanual transfer of the proprioceptive realignment aftereffects of prism adaptation in right-handers by examining alternate target pointing with the two hands for 40 successive trials, 20 with each hand. Adaptation for the right hand was not different as a function of exposure sequence order or postexposure test order, in contrast with adaptation for the left hand. Adaptation was greater for the left hand when the right hand started the alternate pointing than when the sequence of target-pointing movements started with the left hand. Also, the largest left-hand adaptation appeared when that hand was tested first after exposure. Terminal error during exposure varied in cycles for the two hands, converging on zero when the right hand led, but no difference appeared between the two hands when the left hand led. These results suggest that transfer of proprioceptive realignment occurs from the right to the left hand during both exposure and postexposure testing. Such transfer reflects the process of maintaining spatial alignment between the two hands. Normally, the left hand appears to be calibrated with the right-hand spatial map, and when the two hands are misaligned, the left-hand spatial map is realigned with the right-hand spatial map.     

Effects on prism adaptation of duration and timing of visual feedback during pointing

In two experiments, we investigated the effects of duration of visual feedback of the pointing limb and the time (early to late) in the movement when the limb first becomes visible (timing of visual feedback). Timing, rather than duration of visual feedback, proved to have the greater effect on the relative magnitude of visual and proprioceptive adaptation. Visual adaptation increased smoothly with feedback delay, but corresponding decreases in proprioceptive adaptation underwent an additional sharp change when feedback was delayed until about three-fourths of the way to the terminal limb position. These results are consistent with the idea that visual and proprioceptive adaptation are mediated by exclusive processes. Change in the limb position sense (i.e., proprioceptive adaptation) may be produced by visual guidance of the pointing limb, and view of the limb early in the pointing movement seems to be critical for such visual guidance. The limb may be ballistically released as it nears the terminal position, and, thereafter, any opportunity for visual guidance (i.e., view of the limb) is not effective. On the other hand, change in the eye position sense (i.e., visual adaptation) may be mediated by proprioceptive guidance of the eye; the eyes may track the imaged position of the nonvisible limb. Such proprioceptive guidance seems to be solely a function of the distance moved before the limb becomes visible.     

Adaptation to prism-displaced vision: The importance of target-pointing

Two experiments investigated the hypothesis that the experience of manually pointing at visual targets enhances motoric adaptation to prism-displaced vision. Experiment 1 indicated that when adaptation was measured by means of redirected pointing behavior (negative aftereffect) it varied directly with the specificity of the target, the least adaptation occurring when no target was available. This relationship was not observed when adaptation was measured in terms of a shift in the felt position of the prism-exposed hand (proprioceptive shift). Experiment 2 demonstrated that after double the prism-exposure trials used in Experiment 1, target-pointing experience continued to enhance adaptation (as indexed by both types of adaptation measure). In both experiments negative aftereffect was significantly larger than proprioceptive shift for all experimental conditions and the two measures were not correlated. These latter two findings cast doubt on Harris’s notion that negative aftereffect is entirely the result of altered position sense.     

Additivity of components of prismatic adaptation

Ss pointed with each hand at a light or at the unseen toe and looked in the direction of the unseen toe before, during, and after training one arm to point to a visual target which was progressively displaced to one side by a prism. Results show that a proprioceptive change in the trained arm is a universal component of the adaptation. When a change in the eye-head system occurs, it and the proprioceptive change in the arm sum to the total adaptation and it is accompanied by a predictable degree of intermanual transfer of the adaptation, as a felt-position theory of adaptation would predict. However, when there is no change in the eye-head system, the proprioceptive shift is not always sufficient to account for the total adaptive shift.     

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.     

Processing Speed Deficits in Attention Deficit/Hyperactivity Disorder and Reading Disability

The goal of the current study was to test whether deficits in processing speed (PS) may be a shared cognitive risk factor in reading disability (RD) and Attention Deficit/Hyperactivity Disorder (ADHD), which are known to be comorbid. Literature on ADHD and RD suggests that deficits on tasks with a speeded component are seen in both of these disorders individually. The current study examined a wide range of speeded tasks in RD, ADHD, comorbid RD+ADHD, and a control group to test whether RD and ADHD have similar profiles of PS deficits, and whether these deficits are shared by the two disorders. The results suggest that a general PS deficit exists in both clinical groups compared to controls, although children with RD demonstrate greater PS deficits than children with ADHD. Two tests (underadditivity and partial correlations) were conducted to test whether these PS deficits are shared. Since we found that PS deficits were underadditive in the comorbid group and that partialling PS reduced the correlation between RD and ADHD, it appears that PS is a shared cognitive risk factor that may help explain the comorbidity of these two disorders.     

Effects of Movement Duration and Visual Feedback on Visual and Proprioceptive Components of Prism Adaptation

While looking through laterally displacing prisms, subjects pointed sagittally 80 times at an objectively straight-ahead target, completing a reciprocal out-and-back pointing movement every 1, 3, or 6 s. Visual feedback was available early in the pointing movement or only late at the end of movement. Aftereffect measures of adaptive shift (obtained after every 10 pointing trials) showed adaptive change only in limb position sense (i.e., proprioceptive adaptation) when movement duration was 1 s, regardless of visual feedback condition; but as movement duration increased, adaptive change in the eye position sense (i.e., visual adaptation) increased while proprioceptive adaptation decreased, especially for the late visual feedback condition. Regardless of visual feedback condition, proprioceptive adaptation showed the maximal rate of growth with the 1-s movement duration, whereas visual adaptation showed maximal growth with the 6-s movement duration. These results provide additional support for a model of adaptive spatial mapping in which the direction of strategically flexible coordination (guidance) between eye and limb (and consequently the locus of adaptive spatial mapping) is jointly determined by movement duration and timing of visual feedback. An additional effect of movement duration is to determine the rate of discordant inputs. Maximal growth of adaptation occurs when the input rate matches the response time of the spatial mapping function.     

Effects of movement duration and visual feedback on visual and proprioceptive components of prism adaptation

While looking through laterally displacing prisms, subjects pointed sagittally 80 times at an objectively straight-ahead target, completing a reciprocal out-and-back pointing movement ever 1, 3, or 6 s. Visual feedback was available early in the pointing movement or only late at the end of the movement. Aftereffect measures of adaptive shift (obtained after every 10 pointing trials) showed adaptive change only in limb position sense (i.e., proprioceptive adaptation) when movement duration was 1 s, regardless of visual feedback condition; but as movement duration increased, adaptive change in the eye position sense (i.e., visual adaptation) increased while proprioceptive adaptation decreased, especially for the late visual feedback condition. Regardless of visual feedback condition, proprioceptive adaptation showed the maximal rate of growth with the 1-s movement duration, whereas visual adaptation showed maximal growth with the 6-s movement duration. These results provide additional support for a model of adaptive spatial mapping in which the direction of strategically flexible coordination (guidance) between eye and limb (and consequently the locus of adaptive spatial mapping) is jointly determined by movement duration and timing of visual feedback. An additional effect of movement duration is to determine the rate of discordant inputs. Maximal growth of adaptation occurs when the input rate matches the response time of the spatial mapping function.     

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.     

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.     

Development of the third component in prism adaptation: effects of active and passive movement

Adaptation to prismatically displaced vision was assessed using a factorial design involving active or passive exposure movement, active or passive test movement, and target location. Tests of visual shift, ipsilateral and contralateral proprioceptive shift, and ipsilateral and contralateral target-pointing shift were made at the completion of 6, 12, 24, 48, and 96 exposure trials. During the early stages of adaptation (< 48 exposure trials), changes in ipsilateral target pointing were completely accounted for by the sum of the visual and ipsilateral proprioceptive changes. Following longer exposure durations, evidence of a third component was obtained, but only when exposure and test movements were the same (i.e., active-active and passive-passive conditions). The acquisition of such movement-specific response tendencies was interpreted as indicating that the third component represents a change in a central program or schema, which is responsible for guiding a limb to an externally specified location. Target location had no effect on the presence or magnitude of the third component, and there was no indication that the third component transferred intermanually.     

Experiencing the Cross-Sensory Error Signal During Movement Leads to Proprioceptive Recalibration

Abstract

Reaching to targets in a virtual reality environment with misaligned visual feedback of the hand results in changes in movements (visuomotor adaptation) and sense of felt hand position (proprioceptive recalibration). We asked if proprioceptive recalibration arises even when the misalignment between visual and proprioceptive estimates of hand position is only experienced during movement. Participants performed a “shooting task” through the targets with a cursor that was rotated 30° clockwise relative to hand motion. Results revealed that, following training on the shooting task, participants adapted their reaches to all targets by approximately 16° and recalibrated their sense of felt hand position by 8°. Thus, experiencing a sensory misalignment between visual and proprioceptive estimates of hand position during movement leads to proprioceptive recalibration.