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The use of intracameral lidocaine for augmenting analgesia during intraocular surgery is becoming increasingly popular. We report a case of complete visual loss after the use of intracameral lidocaine to repair a traumatic corneal graft dehiscence. Full visual recovery returned several hours after surgery, suggesting this medication's relative lack of retinal toxicity.
A set of 4 experiments evaluated observers' sensitivity to three-dimensional (3-D) length, using both discrimination and adjustment paradigms with computer-generated optical patterns and real objects viewed directly in a natural environment. Although observers were highly sensitive to small differences in two-dimensional length for line segments presented in the frontoparallel plane, their discrimination thresholds increased by an order of magnitude when the line segments were presented at random orientations in 3-D space. There were also large failures of constancy, such that the perception of 3-D length varied systematically with viewing distance, even under full-cue conditions.
Neurological patients with unilateral neglect fail to orient and respond to stimuli on one side, typically the left. A key research issue is whether neglect is exhibited with respect to the left side of the viewer or of objects. When deficits in attentional allocation depend not merely on an object's location with respect to the viewer but on the object's intrinsic extent, shape, or movement, researchers have inferred that attention must be operating in an object-based frame of reference. Simulations of a view-based connectionist model of spatial attention prove that this inference is not logically necessary: Object-based attentional effects can be obtained without object-based frames. The model thus explains away troublesome phenomena for view-based theories of object recognition.
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Neural events underlying perception of coherent motion are generally believed to be hierarchical: information about local motion is registered by spatio-temporal coincidence detectors whose outputs are cooperatively integrated at a subsequent stage. There is disagreement, however, concerning the spatial scale of the neural filters underlying these operations. According to one class of models, motion registration is initially accomplished in parallel at multiple spatial scales, with filters tuned to lower spatial frequencies responsive to larger motion displacements than filters tuned to higher frequencies. According to another scheme, motion analysis involves a single, broadly tuned spatial filter, with optimal displacement dependent on spacing of local elements. Here we use a masking procedure to measure the extent to which dynamic noise depicted at one spatial scale interferes with detection of coherent motion conveyed by image features at another spatial scale. Our results indicate that a single filter, broadly tuned for spatial frequency, is mediating detection of coherent motion. This finding dovetails with known physiological properties of neurons at an intermediate stage of motion processing.
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9 simple outline figures served as stimuli. Each figure was for 60 msec. projected onto a screen 2 m. from the subject. 1 to 5 fixation areas were chosen for the figures; they were unmarked. After training all subjects reported experience of movement, i.e., fixating a given figure at a given fixation area, subjects reported experiencing the figure as lengthening/expanding from the fixation area to full size and immediately thereafter shortening/contracting to the fixation area. Subjects only saw the figure at its full size for a very short movement. When the fixation area was changed for a figure, the experienced movement also changed, but the fully developed figure remained the same. The durations of subjects' experiened movements of the figures, and thereby the durations of subjects' perception of the figures, were measured in milliseconds. For a given subject the durations of perception of all 9 figures were the same. The durations are characteristic of each subject and have proved to remain constant after a period of 1 yr.
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