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.

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.

Implications of prism adaptation asymmetry for unilateral visual neglect: theoretical note.

Asymmetry in intermanual transfer of proprioceptive and visual prism adaptation is reviewed, which suggests asymmetric hemispheric representation of left and right space, directional connection from right to left visual hemispheres, and lateralization of limb motor control. Damage to the right visual hemisphere source of the directional connection could produce the general features of unilateral visual neglect.

Asymmetric visual prism adaptation and intermanual transfer.

The authors hypothesized that failure of visual adaptation to transfer from an individual's exposed right hand to the unexposed left hand arises from hemispheric asymmetry in eye-hand coordination, such that the dominant eye-right-hand system is specialized for action in the right body space. Groups received combinations of exposed dominant or nondominant hands and right or left prismatic displacement. Following prism exposure (terminal feedback), the authors measured aftereffects for proprioceptive straight-ahead and straight-ahead target pointing for both hands. They measured visual straight-ahead aftereffects, starting from the left and right hemispaces. Results were consistent with the prediction: Visual adaptation transfer and additivity occurred when the nondominant left hand was exposed but not when the dominant right hand was exposed. Visual straight-ahead asymmetry appeared when the dominant right hand was exposed to leftward displacement. The authors discuss the implications for the general theory of prism adaptation.

The early bird does not get the worm: time-of-day effects on college students' basic cognitive processing.

We conducted a neuropsychological and cognitive assessment study to determine whether time of day affects cognitive performance. We measured executive control (fluency), processing speed, semantic memory, and episodic memory performance. We followed 56 students across 3 different times of day, testing performance on vocabulary, fluency, processing speed, and episodic memory. Results showed an advantage for fluency and digit symbol task performance in the afternoon and evening testing times relative to morning testing (regardless of testing order), but that time of day did not affect semantic or episodic memory performance. These results suggest that optimal executive functioning and processing speed may occur for typical college students in the afternoon and evening regardless of time-of-day preference.

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.

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.

Prism adaptation and unilateral neglect: review and analysis.

Theory and data from normal prism adaptation are applied toward understanding the ameliorating effects of prism adaptation for left unilateral neglect patients. Neglect is proposed to be, at least in part, a dysfunction in selection of the region of space appropriate for the task at hand. Normally, a task-work space is strategically sized and positioned (calibrated) around the task-relevant objects. Patients show deficits in both strategic abilities: the task-work space is pathologically reduced in size and patients cannot strategically shift its position. Prism adaptation (spatial realignment) ameliorates dysfunctional positioning, but not sizing of the task-work space. Realignment shifts the egocentric coordinates of a sensory-motor reference frame, thereby bringing at least part of the neglected hemispace into the dysfunctional task-work space: prism adaptation substitutes for dysfunctional positioning, but not sizing of a task-work space. However, such amelioration of dysfunctional positioning may enable relearning of strategic processes (calibration), perhaps, even partially restoring the ability to appropriately size the task-space. Investigation of therapeutic prism adaptation requires methods that permit identification of both the calibration dysfunction and ameliorating realignment.

Equipment review: the success of early goal-directed therapy for septic shock prompts evaluation of current approaches for monitoring the adequacy of resuscitation.

A recent trial utilizing central venous oxygen saturation (SCVO2) as a resuscitation marker in patients with sepsis has resulted in its inclusion in the Surviving Sepsis Campaign guidelines. We review the evidence behind SCVO2 and its relationship to previous trials of goal-directed therapy. We compare SCVO2 to other tools for assessing the adequacy of resuscitation including physical examination, biochemical markers, pulmonary artery catheterization, esophageal Doppler, pulse contour analysis, echocardiography, pulse pressure variation, and tissue capnometry. It is unlikely that any single technology can improve outcome if isolated from an organized pattern of early recognition, algorithmic resuscitation, and frequent reassessment. This article includes a response to the journal's Health Technology Assessment questionnaire by the manufacturer of the SCVO2 catheter.

Applications of prism adaptation: a tutorial in theory and method.

Data and theory from prism adaptation are reviewed for the purpose of identifying control methods in applications of the procedure. Prism exposure evokes three kinds of adaptive or compensatory processes: postural adjustments (visual capture and muscle potentiation), strategic control (including recalibration of target position), and spatial realignment of various sensory-motor reference frames. Muscle potentiation, recalibration, and realignment can all produce prism exposure aftereffects and can all contribute to adaptive performance during prism exposure. Control over these adaptive responses can be achieved by manipulating the locus of asymmetric exercise during exposure (muscle potentiation), the similarity between exposure and post-exposure tasks (calibration), and the timing of visual feedback availability during exposure (realignment).

First-trial adaptation to prism exposure: artifact of visual capture.

Terminal target-pointing error on the 1st trial of exposure to optical displacement is usually less than is expected from the optical displacement magnitude. The authors confirmed 1st-trial adaptation in the task of pointing toward optically displaced targets while visual feedback was delayed until movement completion. Measurement of head-shoulder posture while participants (N = 24) viewed the optically displaced field revealed that their shoulders felt turned in the direction opposite to the displacement (visual capture), accounting for all but about 4% to 10% of 1st-trial adaptation. First-trial adaptation was unrelated to realignment aftereffects. First-trial adaptation is largely an artifact of the asymmetry of the structured visual field produced by optical displacement, which induces a felt body rotation, thereby reducing the effective optical displacement.

Dual prism adaptation: calibration or alignment?

Dual adaptation to different amounts or directions of prismatic displacement, or both, can be acquired and maintained with little mutual interference. Associative recalibration of the regional task- or workspace, contingent on differentiation of distinguishing sensory information, can explain such adaptation. In contrast, nonassociative realignment restores dimensional mapping among spatial representations. Methods for measuring the separate contributions of those 2 kinds of prism adaptation are identified in the present article. On the basis of a critique of dual-adaptation studies, the authors suggest that recalibration can explain the data but that the method used in those experiments confounded realignment and might have obscured the effectiveness of dual-calibration training.

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.

Strategic calibration and spatial alignment: a model from prism adaptation.

Two types of adaptive processes involved in prism adaptation have been identified&colon: Slower spatial realignment among the several unique sensorimotor coordinate systems (spatial maps) and faster strategic motor control responses(including skill learning and calibration) to spatial misalignment. One measures the 1st process by assessing the aftereffects of prism exposure, whereas direct effects of the prism during exposure are a measure of the 2nd process. A model is described that relates those adaptive processes and distinguishes between extraordinary alignment and ordinary calibration. A conformal translation algorithm that operates on the hypothesized circuitry is proposed. The authors apply to the model to explain the advantage of visual calibration when the limb is seen in the starting position prior to movement initiation. Implications of the model for the use of prism adaptation as a tool for investigation of motor control and learning are discussed.