Abstract

The present study demonstrated that the magnitude of after-effect due to wedge prisms depends on the form of the visual feedback used to represent hand and target position in fast, targeted, transverse reaches. Trained human subjects made reaches with and without prisms in three visuomotor representations (VR): (1) the subject’s actual hand and targets (Direct), (2) a real-time video broadcast of hand and targets (Video), or (3) abstract, computer-generated targets and a cursor representing hand position (Cursor). A significant after-effect occurred in each VR. However, the magnitude of the after-effect was significantly different among VRs: the magnitude was greatest in Direct, smaller in Video and smallest in Cursor. A significant after-effect (carryover) also occurred when a subject prism-adapted reaches in one VR and then removed the prisms and made initial reaches in another VR. Our data showed that when reaches were prism-adapted in Direct and then prisms were removed, there was a large carryover to initial reaches in Video or Cursor (D→V and D→C). In contrast, when prisms were worn in Video and removed for reaches in Direct (V→D), there was a significantly smaller carryover than from both D→V and D→C. Finally, when prisms were worn in Cursor and removed for reaches in Direct (C→D), there was very little detectable carryover. Our results suggest that adaptation is context-dependent and that the magnitude of carryover is dependent on the VR in which adaptation occurred. Interpretations of adaptations made in abstract training and experimental conditions may be greatly affected by this finding.

Abstract

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 Once the prisms are withdrawn, the degree and strength of the adaptation can be measured by the spatial deviation of the motor actions in the direction opposite to the visual displacement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.

American Journal of Psychology: Vol. 79, No. 3, p. 443

American Journal of Psychology: Vol. 87, No. 1/2, p. 197

Abstract

 

American Journal of Psychology: Vol. 77, No. 3, p. 457

Sheidt, R.A., Conditt, M.A., Secco, E.L., Mussa-Ivaldi, F.A. (2005), Interaction of visual and proprioceptive feedback during adaptation of human reaching movements, Journal of Neurophysiology, 93, 3200-3213.  

Abstract

People tend to make straight and smooth hand movements when reaching for an object. These trajectory features are resistant to perturbation, and both proprioceptive as well as visual feedback may guide the adaptive updating of motor commands enforcing this regularity. How is information from the two senses combined to generate a coherent internal representation of how the arm moves? Here we show that eliminating visual feedback of hand-path deviations from the straight-line reach (constraining visual feedback of motion within a virtual, "visual channel") prevents compensation of initial direction errors induced by perturbations. Because adaptive reduction in direction errors occurred with proprioception alone, proprioceptive and visual information are not combined in this reaching task using a fixed, linear weighting scheme as reported for static tasks not requiring arm motion. A computer model can explain these findings, assuming that proprioceptive estimates of initial limb posture are used to select motor commands for a desired reach and visual feedback of hand-path errors brings proprioceptive estimates into registration with a visuocentric representation of limb position relative to its target. Simulations demonstrate that initial configuration estimation errors lead to movement direction errors as observed experimentally. Registration improves movement accuracy when veridical visual feedback is provided but is not invoked when hand-path errors are eliminated. However, the visual channel did not exclude adjustment of terminal movement features maximizing hand-path smoothness. Thus visual and proprioceptive feedback may be combined in fundamentally different ways during trajectory control and final position regulation of reaching movements.

Science: New Series, Vol. 140, No. 3568, p. 812

Sober, S.J. & Sabes, P.N. (2005), Flexible strategies for sensory integration during motor planning, Nature Neuroscience, 8, 490-497. 

Redding, G.M., Wallace, B., Effects of pointing rate and availability of visual feedback on visual and proprioceptive components of prism adaptation, Journal of Motor Behavior, 24.3, 226-237. 

Abstract

When the limb becomes visible early in a pointing movement proprioceptive adaptation is greater than visual, but if visual feedback is delayed until the end of the movement the reverse is true. However, this effect occurs only if pointing rate is low. With high rates, adaptation is proprioceptive in nature regardless of feedback availability.

Abstract

Adaptation to the simple visual displacement of prisms was compared to that for refractive lenses, which have a varied prismatic effect. Subjects were made myopic using contact lenses, then corrected using spectacle lenses. The effect on the perceived direction of a randomly located target was assessed from pointing behavior. Prism adaptation showed a negative directional aftereffect but lacked intermanual transfer. Lens adaptation lacked a negative aftereffect but exhibited intermanual transfer. The results suggest that lens adaptation involves a recalibration of extraretinal eye movement information and multiple sets of lens adaptation can be retained for short periods.

American Journal of Psychology: Vol. 76, No. 4, p. 568

Different factors may determine the displacements in reaching that occur as a result of wearing prism glasses. Both visual and propioceptive factors are probably involved, but in previous studies, visual factos have been underemphasized. These experiments explored whether prism after-effects could be confined to a specific portion of the visual field. This would rule out a purely proprioceptive-motor hypothesis.

Subjects wore goggles over one eye with the other eye occluded. This allowed a monocular visual field of 60 degrees. Objects in the visual field were displaced by 22 degrees from their true position. Subjects were asked to look at the reflection of a target in a mirror so placed that the target appeared to lie on the horizontal surface of a table. The subject could mark the apparent position of the targets, but the mirror concealed his hands and marks, so subjects could not see or correct errors of localization. There were 3 phases of each experiment. The first was the pre-exposure phase in which the subject marked the apparent position of the target points. Then there was an exposure period of 1-min in which the subject with goggles on reached for a target and could see his active hand. When the exposure period was over, the goggles were removed and the subject repeated the same marking procedure as in pre-exposure. The difference in position between the pre-exposure and post-exposure markings served as a measure of the size of the Displacement after-effect.

Experiment I - adaptation to induced displacement in a limb seen through the prism, but not moved by the subject.
In the pre-exposure phase, subjects marked the apparent location of the target with the active hand first and then with the passive hand. During the exposure period, goggles were put on and the active hand was used to mark the target. In one condition, the passive hand was visible. In the other condition, the passive hand was held outside of the field of view. In the post-exposure phase, the subjects marked the location of the target with the passive hand and then the active hand to distinguish between visual and proprioceptive explainations for the DAE. Subjects showed a significant DAE when marking with the passive hand if it had been visible during the exposure period, but not if the hand had not been visible.

Experiments II & III - exposure of a limited retinal area to the prism to study the transfer of DAE between the central and peripheral regions of retina.
In the pre-exposure phase, subjects marked the location of three targets at 20 degree intervals across the visual field while fixating in the center of the field (so that peripheral areas of the retina were used when marking the lateral target points). In one exposure condition, the visual field through the prism was limited to 10 degrees. In the second condition, the goggles were masked to allow a 15 degree horizontal and a 10 degree vertical field at the periphery of the goggles' field, but there was also a pinhole in the center allowing the subject to hold fixation. The two conditions achieved differential stimulation of the central and peripheral retinal areas.
If subjects saw their hands moving in the central 10 degrees of the visual field, they showed equally large after-effects at all targets. If the subjects only saw their displaced hand in the periphery of the retina, the after-effects were greater on the exposed side of the field than on the other parts. Experiment III was the same except fixation was not required during the post-exposure phase. In this case, there was not difference in DAE for a central or lateral target.

The critical factor in the production of intermanual trasnfer of DAE was the presence of the passive hand in the visual field while the active hand was seen moving. When the passive hand was not in the field, there was no opportunity for a combined input to reach the comparator.

Abstract

Clower, Dottie M. and Driss Boussaoud. Selective Use of Perceptual Recalibration Versus Visuomotor Skill Acquisition. J. Neurophysiol. 84: 2703-2708, 2000. Exposure to laterally displacing prisms is characterized by systematic misreaching in the opposite direction after prisms are removed. Other learning tasks involving altered visuomotor mappings can often be mastered by the subject with minimal resulting aftereffects. One variable that may account for this difference is the nature of the feedback provided to the subject: during studies of prism exposure, subjects usually view the hand itself, whereas in many studies of visuomotor learning, subjects view a computer-generated representation of the hand position or movement. We compared the use of actual feedback of the hand with computer-generated representational feedback of its position during exposure to laterally displacing prisms. In the actual feedback condition (ACT), a light on the fingertip was illuminated immediately at the end of each reach. In the representational feedback condition (REP), a computer-generated spot of light was displayed to indicate the exact position of the fingertip at the end of each reach. Whereas the rate and magnitude of error correction were the same in both conditions, only the ACT condition produced the large adaptive aftereffect typically observed after prism exposure. These results suggest that the perception of a physical coincidence between the feedback source and the hand may be a key factor in determining whether adaptation is accomplished through perceptual recalibration or visuomotor skill acquisition.

Haijiang et al. 103 (2): 483 -- Proceedings of the National Academy of Sciences

Abstract

Until half a century ago, associative learning played a fundamental role in theories of perceptual appearance [Berkeley, G. (1709) An Essay Towards a New Theory of Vision (Dublin), 1st Ed.]. But starting in 1955 [Gibson, J. J. & Gibson, E. J. (1955) Psychol. Rev. 62, 32-41], most studies of perceptual learning have not been concerned with association or appearance but rather with improvements in discrimination ability. Here we describe a "cue recruitment" experiment, which is a straightforward adaptation of Pavlov's classical conditioning experiment, that we used to measure changes in visual appearance caused by exposure to novel pairings of signals in visual stimuli. Trainees viewed movies of a rotating wire-frame (Necker) cube. This stimulus is perceptually bistable. On training trials, depth cues (stereo and occlusion) were added to force the perceived direction of rotation. Critically, an additional signal was also added, contingent on rotation direction. Stimuli on test trials contained the new signal but not the depth cues. Over 45 min, two of the three new signals that we tested acquired the ability to bias perceived rotation direction on their own. Results were consistent across the eight trainees in each experiment, and the new cue's effectiveness was long lasting. Whereas most adaptation aftereffects on appearance are opposite in direction to the training stimuli, these effects were positive. An individual new signal can be recruited by the visual system as a cue for the construction of visual appearance. Cue recruitment experiments may prove useful for reexamining of the role of experience in perception.

Research for a Psyc211-Perceptual Learning Term Paper

 Child Development: Vol. 52, No. 2, p. [463]

Abstract

 

The Washington Post site dedicated to the film. Includes links to other sites with information about Watergate and the film, as well as the original news story by Woodward and Bernstein.

    Chapter 6 of Journalism in the Movies deals with films about conspiracy and paranoia. Ehrlich argues that the collapse of the Production Code, Vietnam, Watergate, stagflation, and other factors contributed to a general feeling of mistrust and angst in the 1970’s and that this feeling was reflected in the films made during the decade. To make his argument, he focuses on movies that center around the media and with journalists as crusaders against evil and corruption. Specifically, he compares the style and content of All the President’s Men and Network. While All the President’s Men portrays the men who work for the newspaper as “a shining beacon of truth,” Network focuses on a television network that is part of a larger evil involving the rest of corporate America. Additionally, while the former film was produced in documentary style, the later is exaggerated and satirical.
    More than any other aspect of the film, the image of the two young reporters remains in the minds of those who have seen it. Yet, as has been discussed at length, there is a controversy surrounding the accuracy of the portrayal of the journalists. Ehrlich analyzes the validity of this controversy by comparing he actual events of Watergate with the account of the journalists’ role in these events in the movie. According to Ehrlich, Nixon was reelected despite Woodward and Bernstein’s investigation, and he did not run into serious political trouble until the Senate hearings that occurred a year after the first article was published in the Washington Post. In fact, Nixon did not resign until after the book by the same name as the film was published. So, Ehrlich concludes, the reporters were certainly not responsible for Nixon’s fall from glory. However, the film accentuates their role by establishing the main characters as “fearless foes of corruption” in a mysterious and believable “documentary-noir” style executed by director Alan J. Pakula. The movie is relatively straightforward in its analysis of good and evil. The office of the Washington Post is brightly lit, while most of the rest of Washington D.C. is shrouded in darkness.
    As a result of their portrayal in All the President’s Men, Woodward and Bernstein have become the central players in America’s collective memory of Watergate. The screenwriter, Goldman, cut out parts of the book involving the senate hearings and many government figures who helped bring down the president, assuming that the audience could “fill in the rest of the story for themselves.” In 1976, this may have been the case. However, the movie has helped to determine which aspects of the story have been transferred “from fact to legend,” and the parts that we are expected to fill in become markedly less glamorous without the benefit of handsome actors and the infusion of drama through “shadowy scenes.” Even today, Woodward and Bernstein “remain securely ensconced in American mythology.”

An Annotated Bibliography of the film for FILM101 with Peter Decherney, Spring 2006. Researched and written by Jennifer Klein.

The IMDB site for All the President's Men, starring Robert Redford and Dustin Hoffman. Directed by Alan J. Pakula.