The interaction of vision and audition in two-dimensional space.

Using a mouse-driven visual pointer, 10 participants made repeated open-loop egocentric localizations of memorized visual, auditory, and combined visual-auditory targets projected randomly across the two-dimensional frontal field (2D). The results are reported in terms of variable error, constant error and local distortion. The results confirmed that auditory and visual maps of the egocentric space differ in their precision (variable error) and accuracy (constant error), both from one another and as a function of eccentricity and direction within a given modality.

Achilles allograft reconstruction for recurrent dislocation in total hip arthroplasty.

Recurrent dislocation secondary to posterior soft tissue deficiency is a challenging complication of total hip arthroplasty. We describe the use of an Achilles allograft sling to improve hip stability. Eight patients treated with the sling were followed an average of 5 years.

Cognitive performance during prismatic displacement as a partial analogue of "space fog".

Background: The fact that microgravity adaptation and recovery from the cognitive deficit of "space fog" follow approximately the same time course raises the possibility that they are related to one another. Two experiments tested this hypothesis.

Methods: Because microgravity adaptation is unique to outer space, we investigated the Earth-based analogue of adapting to prismatic displacement.

Egocentric and allocentric localization during induced motion.

This research examined motor measures of the apparent egocentric location and perceptual measures of the apparent allocentric location of a target that was being seen to undergo induced motion (IM). In Experiments 1 and 3, subjects fixated a stationary dot (IM target) while a rectangular surround stimulus (inducing stimulus) oscillated horizontally. The inducing stimulus motion caused the IM target to appear to move in the opposite direction.

The relationship between perceived length and egocentric location in Müller-Lyer figures with one versus two chevrons.

We examined the apparent dissociation of perceived length and perceived position with respect to the Müller-Lyer (M-L) illusion. With the traditional (two-chevron) figure, participants made accurate open-loop pointing responses at the endpoints of the shaft, despite the presence of a strong length illusion. This apparently non-Euclidean outcome replicated that of Mack, Heuer, Villardi, and Chambers (1985) and Gillam and Chambers (1985) and contradicts any theory of the M-L illusion in which mislocalization of shaft endpoints plays a role.

Studies of open-loop pointing in the presence of induced motion.

In the present research, we examined the influence of induced motion (IM) on open-loop pointing responses and the possibility that IM alters the registration of either eye or trunk position. In two experiments, subjects tracked a dot that oscillated vertically while a rectangular stimulus oscillated horizontally. The pairing of frame and dot motion caused the dot to appear to move on a slant, due to IM.

Visually perceived eye level with reversible pitch stimuli: implications for the great circle and implicit surface models.

Visually perceived eye level (VPEL) and perceived pitch were measured while subjects viewed two sets of stimuli that were either upright or pitched top-toward or top-away from them. The first set of stimuli, a pair of vertical lines viewed at various angles of pitch, caused systematic changes in perceived pitch and upward and downward VPEL shifts for the top-toward and top-away pitches, respectively. Neither the perceived pitch nor the VPEL measures with these stimuli differed between monocular and binocular viewing.

Treatment of the unstable total hip arthroplasty using modularity, soft tissue, and allograft reconstruction.

This is a retrospective analysis of a stepwise approach to the treatment of the unstable total hip arthroplasty. Thirty-two hips in 32 patients were analyzed 9 months to 7 years (average, 3.6 years) after reoperation for instability.

How can we determine if the sense of presence affects task performance?

The question of whether the sense of presence in virtual environments (or telepresence with respect to teleoperator systems) is causally related to task performance remains un-answered because the appropriate studies have yet to be carried out. In this brief report, the author describes a strategy for resolving this issue and the results of a pilot study in which this strategy was implemented.

Contributions of object- and space-based mechanisms to line bisection errors.

In two experiments, normal adults divided a horizontal line segment and an equal spatial interval that did not contain a line into eight equal-appearing segments by means of successive bisections. In the first experiment, subjects' average initial bisections erred to the left of objective center for both stimuli. Their subsequent bisections produced similar errors for the line-present stimulus, as the bisection of each progressively smaller line segment was placed to the left of true center.

Effects of gravitational and optical stimulation on the perception of target elevation.

To examine the combined effects of gravitational and optical stimulation on perceived target elevation, we independently altered gravitational-inertial force and both the orientation and the structure of a background visual array. While being exposed to 1.0, 1.

Why do pitched horizontal lines have such a small effect on visually perceived eye level?

In two experiments, visually perceived eye level (VPEL) was measured while subjects viewed two-dimensional displays that were either upright or pitched 20 degrees top-toward or 20 degrees top-away from them. In Experiment 1, it was demonstrated that binocular exposure to a pair of pitched vertical lines or to a pitched random dot pattern caused a substantial upward VPEL shift for the top-toward pitched array and a similarly large downward shift for the top-away array. On the other hand, the same pitches of a pair of horizontal lines (viewed binocularly or monocularly) produced much smaller VPEL shifts.

Relative spatial expansion and contraction within the Müller-Lyer and Judd illusions.

The shaft portions of Müller-Lyer (M-L) figures, one-ended M-L figures, Judd figures, and their respective control (tails-up) figures were divided by subjects into eight equal-appearing intervals by means of successive bisections. For most of the control stimuli the length of the left half of the shaft tended to be overestimated relative to the length of the right side. For the tails-out version of the M-L figure, there was relative overestimation of segments of the shaft adjacent to the tails, while for the tails-in version there was relative underestimation of these segments.

An analysis of blood management in patients having a total hip or knee arthroplasty.

Three hundred and thirty orthopaedic surgeons in the United States participated in a study of transfusion requirements associated with total joint arthroplasty. A total of 9482 patients (3920 patients who had a total hip replacement and 5562 patients who had a total knee replacement) were evaluated prospectively from September 1996 through June 1997. Of those patients, 4409 (46 percent [57 percent of the patients who had a hip replacement and 39 percent of the patients who had a knee replacement]) had a blood transfusion.

Dual adaptation and adaptive generalization of the human vestibulo-ocular reflex.

In two experiments, we examined the possibility that the human vestibulo-ocular reflex (VOR) is subject to dual adaptation (the ability to adapt to a sensory rearrangement more rapidly and/or more completely after repeated experience with it) and adaptive generalization (the ability to adapt more readily to a novel sensory rearrangement as a result of prior dual adaptation training). In Experiment 1, the subjects actively turned the head during alternating exposure to a visual-vestibular rearrangement (target/head gain = 0.5) and the normal situation (target/head gain = 0.

Dual adaptation of apparent concomitant motion contingent on head rotation frequency.

Perceived movement of a stationary visual stimulus during head motion was measured before and after adaptation intervals during which participants performed voluntary head oscillations while viewing a moving spot. During these intervals, participants viewed the spot stimulus moving alternately in the same direction as the head was moving during either .25- or 2.

Samuel Theobald M.D. Ophthalmology at the Johns Hopkins Hospital before the Wilmer Institute 1889-1925.

Although ophthalmology today at the Johns Hopkins Hospital is synonymous with the name of Wilmer, it should be remembered that the Wilmer Ophthalmological Institute was not founded until 1925. Thus, to appreciate fully the ophthalmic heritage of Johns Hopkins we must look back to the beginnings of the medical institutions. When the Johns Hopkins Hospital opened in 1889 and the medical school followed in 1893, Samuel Theobald, M.

On the origin of eye movement desensitization and reprocessing: a response to Rosen.

Rosen argues that the eye movements experienced by Shapiro during the incident leading to her development of eye movement desensitization and reprocessing (EMDR) could not, as she later inferred, have been saccadic. The present author disputes Rosen's conclusion by showing that his arguments are based on a faulty understanding of the nature of saccadic eye movements or are irrelevant to Shapiro's claim.

Accuracy and adaptation of reaching and pointing in pitched visual environments.

Visually perceived eye level (VPEL) and the ability of subjects to reach with an unseen limb to targets placed at VPEL were measured in a statically pitched visual surround (pitchroom). VPEL was shifted upward and downward by upward and downward room pitch, respectively. Accuracy in reaching to VPEL represented a compromise between VPEL and actual eye level.

The role of retinal versus perceived size in the effects of pitched displays on visually perceived eye level.

Visually perceived eye level (VPEL) was measured while subjects viewed two vertical lines which were either upright or pitched about the horizontal axis. In separate conditions, the display consisted of a relatively large pair of lines viewed at a distance of 1 m, or a display scaled to one third the dimensions and viewed at a distance of either 1 m or 33.3 cm.

Is there dissociation of perceptual and motor responses to figural illusions?

Open-loop reaching for locations within figural illusions was measured in three experiments. The experiments differed with respect to whether subjects were provided a visible target toward which to direct their reaching or were required to form a mental representation of the intended target. In the first experiment, subjects' reaching errors for vertices of a Müller-Lyer figure were similar to those for a nonillusory control stimulus.

Reduction of the elevator illusion from continued hypergravity exposure and visual error-corrective feedback.

Ten subjects served as their own controls in two conditions of continuous, centrifugally produced hypergravity (+2 Gz) and a 1-G control condition. Before and after exposure, open-loop measures were obtained of (1) motor control, (2) visual localization, and (3) hand-eye coordination. During exposure in the visual feedback/hypergravity condition, subjects received terminal visual error-corrective feedback from their target pointing, and in the no-visual feedback/hypergravity condition they pointed open loop.

Multiple concurrent visual-motor mappings: implications for models of adaptation.

Previous research on adaptation to visual-motor rearrangement suggests that the central nervous system represents accurately only 1 visual-motor mapping at a time. This idea was examined in 3 experiments where subjects tracked a moving target under repeated alternations between 2 initially interfering mappings (the "normal" mapping characteristic of computer input devices and a 108 degree rotation of the normal mapping). Alternation between the 2 mappings led to significant reduction in error under the rotated mapping and significant reduction in the adaptation aftereffect ordinarily caused by switching between mappings.

The dissection of intersensory bias: weighting for Radeau.

In my commentary on Monique Radeau's comprehensive and enlightening review I will (1) discuss methodological problems and their solution, (2) distinguish "intersensory bias" from the related process of adaptation, (3) elaborate on the likely mechanism by which intersensory bias operates, and (4) address Radeau's contention that ventriloquism is "cognitively impenetrable."