Generalization of prism adaptation

Prism exposure produces 2 kinds of adaptive response. Recalibration is ordinary strategic remapping of spatially coded movement commands to rapidly reduce performance error. Realignment is the extraordinary process of transforming spatial maps to bring the origins of coordinate systems into correspondence. Realignment occurs when spatial discordance signals noncorrespondence between spatial maps. In Experiment 1, generalization of recalibration aftereffects from prism exposure to postexposure depended upon the similarity of target pointing limb postures. Realignment aftereffects generalized to the spatial maps involved in exposure. In Experiment 2, the 2 kinds of aftereffects were measured for 3 test positions, one of which was the exposure training position. Recalibration aftereffects generalized nonlinearly, while realignment aftereffects generalized linearly, replicating Bedford (1989, 1993a) using a more familiar prism adaptation paradigm. Recalibration and realignment require methods for distinguishing their relative contribution to prism adaptation.     

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.     

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.     

Individual differences in the visual component of prism adaptation

The centrality of individual differences in the visual component of perceptual adaptation was examined in a massed-practice-terminal-exposure, prism-viewing paradigm. With positive (adaptive) adjustments in the judgment of the visual straight-ahead, target-pointing aftereffects were found to be equivalent to the sum of the visual and proprioceptive (head-arm) aftereffects. For subjects showing negative visual adjustments to prism exposure, the target-pointing aftereffect was not significantly different from the change in proprioception alone. Implications of these findings for hypotheses concerning the process of perceptual adaptation are discussed.     

Restricted adaptation to prism rearrangement

Changes in eye-foot and eye-hand coordination were measured following 20 min of squint prism viewing (alternate monocular viewing of the movements of each leg with the contralateral eye at 1-min intervals: prism base right for right eye and left for left eye). In different sessions, response changes were measured following the viewing of the left leg with the right eye (prism base right) for periods of i min interspersed with 1-min blank periods (periodic viewing). Sensorimotor changes following the alternate exposure condition were smaller and restricted to eye-foot responses.     

Adaptation of the two arms to opposite prism displacements

In normal subjects, the two arms were exposed separately to prismatic displacements of opposite sign, using the eye ipsilateral to the exposed arm. Opposite adaptive shifts were induced on each arm whether the eye ipsilateral to the arm (i.e. exposed to a displacement of the same sign as the arm) or the eye controlateral to the arm (i.e. exposed to a displacement of opposite sign) was used during testing. This result precludes the possible role of oculomotor signals in this type of prism adaptation.     

First-trial adaptation to prism exposure

Terminal target-pointing error on the 1st trial of exposure to optical displacement is usually less than that expected from the optical displacement magnitude. Such 1st trial adaptation was confirmed in 2 experiments (N = 48 students in each) comparing pointing toward optically displaced targets and toward equivalent physically displaced targets (no optical displacement), with visual feedback delayed until movement completion. First-trial performance could not be explained by ordinary target undershoot, online correction, or reverse optic flow information about true target position and was unrelated to realignment aftereffects. Such adaptation might be an artifact of the asymmetry of the structured visual field produced by optical displacement, which induces a felt head rotation opposite to the direction of the displacement, thereby reducing the effective optical displacement.     

Long-lasting aftereffect of brief prism exposure

The aftereffect of 15 min of active adaptation to wedge prism displacement was shown to persist for as long as 2 weeks.     

A color-contingent prism displacement aftereffect

Observers were trained to point with feedback to red and blue dots whose images had been laterally displaced in opposite directions by a reversible prism. On pretraining and posttraining trials the red and blue dots were aligned vertically in the absence of visual orientation cues. The alignment was modified by the pointing training on the posttraining trials. The colors were aligned in the direction of their prior prismatic displacement. One control experiment showed that the alignment aftereffect requires feedback during the pointing task. Another experiment in which observers pointed to the red and blue dots with opposite arms showed that pointing to both dots with the same arm was necessary to produce the alignment aftereffect. Changes in the perceived position of objects in the visual field occur when changes in perceived limb position cannot compensate for a sensorimotor conflict. Eye torsion or fixation displacements are proposed as alternative mechanisms mediating the aftereffect.     

Porous skin: Breathing through the prism of the holey body

The skin is a body's largest organ and both a metaphor and a materiality. It constitutes a person's exteriority through which and on which social meaning is negotiated and constructed. My contribution challenges the modern idea of the skin's imagined solidity and fixity by returning to an older set of ideas that approach the body as porous, relational, ambiguous and atmospheric. The thought of a body that is open, holey from both the inside and the outside, atmospheric, strikes against culturally constructed and carefully policed myths and norms of groundedness and boundedness. Porosity, however, has not always been feared in that way. My paper explores the ways in which older, speculative thought celebrated the skin's ability to mingle corporally with air, wind and world. This radical openness affectively and materially ‘ungrounds’ seemingly familiar feelings and expectations of order, sense and stability. I wish to retrieve some of this original thinking, which approaches the body not as surface but through its glands, crevices, pores and holes that blur dichotomies of inside and outside. The purpose is to offer an embodied and relational politics that starts from a breathable skin that makes emotion and affect more contingent on the body's holey relationship to air and atmosphere.     

No retinal component in prism adaptation

Cohen's (1966) report of a retinal component in adaptation to prisms was re-examined and some possible artifacts identified. An experiment is briefly reported that overcame these problems. Although adaptation of registered eye position was found, there was no evidence for any retinal involvement.     

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.