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Biomedical subjects

W L Larson

Publications and source records attributed to W L Larson.

At least 37 records · Page 2Linked to original sources
PubMed1988

Effect of TNO red-green glasses on local stereoacuity.

Local stereoacuity was reduced when red-green anaglyph glasses were worn. Glasses were from the TNO stereotest. Without these glasses, all 15 subjects had good or almost good local stereoacuity. With the glasses, all stereoacuities were reduced but one subject still had a good stereoacuity of 8 sec arc. Reductions with the TNO anaglyph glasses ranged from 2 to 34 sec arc. The TNO test was also performed to see if there was a difference between local and global stereoacuity while wearing the glasses. Results were similar for 6 subjects, all of whom had the best TNO stereoacuity of 15 sec arc. Global (TNO) stereoacuity was worse than local stereoacuity for the other subjects with the most extreme difference being 464 sec arc. If aniseikonia was induced by the red-green glasses, this could not have contributed to a reduction in either local or global stereoacuity.

Color↗
PubMed1988

Stereoacuity testing: an illusion of tilt when viewing two parallel vertical rods or lines.

When stereoacuity was measured, some subjects (but not all) saw the two vertical rods of the test to be tilted. The perceived tilt indicated that the top of a rod was nearer to or farther from the observer than the bottom. Sometimes one rod appeared tilted and sometimes both. It was rare for both to appear tilted in the same direction. There are 9 possible tilt combinations including both rods vertical. All were observed but only 1 of the 3 subjects observed them all. In some instances, the frequency with which a particular tilt combination was seen was influenced by which rod was nearer and by the binocular disparity presented by the rods. During a stereoacuity test, tilt can confuse the identification of the nearer rod. Uncertainty is avoided by regarding the middle of the rods. Lines drawn on paper were also seen to tilt by some subjects.

Adult↗
PubMed1987

Does a small field of view degrade stereoacuity?

It was reported, in 1968, that stereoacuity became worse as the binocular field of view was reduced. Reported here are attempts to replicate this finding with a different stereoacuity test and with a simulation of the original test. Results suggest that the phenomenon is idiosyncratic because most subjects showed no loss in stereoacuity with the smallest field of view used in the original investigations (3.8 degrees). The greatest decrease in stereoacuity in this sample of nine subjects was 6 sec arc. These results are compared with those found in the original investigations and differences discussed.

Depth Perception↗
PubMed1985

Illusory differences which are stereoacuity test cues.

Some persons perceive an illusion of unequal blackness when viewing two equally black rods in a stereoacuity test. With binocular vision, the blacker rod is usually the nearer of the two. If blackness is used as a cue to nearness, a stereoacuity test can be performed successfully without using stereopsis. Nevertheless, stereoacuity obtained by this means is usually inferior to that obtained with distance judgments. For this reason it is advisable to warn subjects against using a blackness difference as a cue to the nearer rod. Those who saw this illusion binocularly also saw it monocularly. Therefore, it is more than just an artifact of stereopsis. One person observed an illusory difference in rod width as well as blackness.

Cues↗
PubMed1985

Does the Howard-Dolman really measure stereoacuity?

The Howard-Dolman (H-D) is a version of Howard's stereoacuity test (H) which has almost completely eclipsed the original. However, there is reason to believe that the H-D is not as good a test as the H. To find out whether or not the H-D gave results similar to the H, 34 subjects were tested by both procedures with the same stereoacuity tester. This was fully automated and programmable. There are at least four ways of relating H-D findings to stereoacuity. None of these gave results comparable to those found with the H. Therefore, the H-D may be of questionable worth for clinical and scientific use. The same conclusion can be drawn regarding the relation between the H-D constant error and aniseikonia.

Depth Perception↗
PubMed1983

Stereoscopic acuity with induced refractive errors.

The relation between refractive error and stereoscopic acuity was investigated by measuring stereoacuity with different combinations of positive and negative spherical lenses over the usual refractive correction. A detailed study was performed on two subjects. In general, there was little change in stereoacuity when the added lenses were of equal power. On the other hand, power inequality almost invariably caused a reduction in stereoacuity. A technique is described for detecting a refractive overcorrection by means of a sequence of stereoacuity measurements.

Dominance, Cerebral↗
PubMed1982

Uncertainty in the measurement of fixation disparity due to zones of perceived nonius alignment.

Fixation disparity was measured by means of limits within which nonius alignment was perceived. Two pairs of limits were found, one starting from perceived alignment and the other starting from perceived misalignment. These limits outline zones of perceived alignment of nonius lines. The extent of the zone of first perceived misalignment was found to be greater than that of first perceived alignment. The zone width can be expressed either in terms of disparity at a particular prism vergence or as a range of prism vergence at a particular disparity. The latter expression is comparable to what has been called the range of zero-associated phoria.

Computers↗
PubMed1979

A laser retinoscope.

A retinoscope that uses a He-Ne laser as its light source has been designed. By this means it is possible to improve the performance of the conventional retinoscope. In particular the contrast of the fundus reflex has been enhanced and the retinoscope can be used at a greater working distance than usual. By using a polarized laser the specular reflections from the eye are completely suppressed. The retinoscope lends itself to refractions under normal room illumination. Patients find the light from the laser retinoscope less bothersome than that of the usual tungsten filament lamp. Advantages and disadvantages of the unit are discussed.

Helium↗
PubMed1978

Microspectrophotometric studies on the visual pigment in the intact retina of the goldfish, Carassius auratus (Linn.).

The visual pigments in intact retinas of the common goldfish were examined by microspectrophotometry. Difference spectra free of photoproduct contamination had absorbance maxima at lambda527 nm +/- 2 nm. The average pigment density, about 0.32, was almost invariant with regard to retinal location and specimen size. Traces of a photoproduct absorbing maximally at lambda480-490 nm were found. The normalized "absorbance" curve deviated from standard templates. It was suggested that this was an effect of cross-coupling of energy and among photoreceptors. Finally, known action spectra show a red shift relative to the absorbance spectra measured.

Animals↗