Biomedical subjects

L N Reich

Publications and source records attributed to L N Reich.

5 recordsLinked to original sources

PubMed2000

Dynamic random noise shrinks the twinkling aftereffect induced by artificial scotomas.

Physiological alterations in cortical neurons are induced during adaptation to an artificial scotoma, a small homogeneous patch within a dynamic random noise or patterned background. When the dynamic noise is replaced by an equiluminant gray background, a twinkling aftereffect can be seen in the location of the artificial scotoma. Following binocular adaptation, we discovered that the perceived size of the twinkling aftereffect was dramatically smaller than the inducing artificial scotoma. Dichoptic adaptation induced shrinkage in the twinkling aftereffect that was similar to that found after binocular adaptation, suggesting that the twinkling aftereffect and its shrinkage both have cortical origins. We speculate that this perceptual shrinkage may reflect the interaction between two cortical mechanisms: a twinkling aftereffect mechanism that spreads throughout the artificial scotoma, and a filling-in mechanism that has a greater influence at the edges of the artificial scotoma and spreads inwards.

Adaptation, Ocular↗

PubMed2000

Relative legibility and confusions of letter acuity targets in the peripheral and central retina.

BACKGROUND: Patients with macular disease may image optotypes at a peripheral retinal locus during visual acuity testing. In this study, we asked if the relative legibility and confusions between letters are similar in the fovea and at 10 degrees in the peripheral retina. METHODS: Twenty five upper-case alphabet letters (all except "I"), constructed to the same specifications as the Sloan letters, were presented one at a time on a computer monitor at the fovea and at 10 degrees in the temporal, superior and superior-temporal retina. RESULTS: The range of relative legibility at peripheral loci was generally larger than in the fovea, for all letters and for the subset of 10 Sloan letters. Although many confusion pairs were similar in the fovea and periphery, additional confusion pairs, preferentially involving curved letters, occurred uniquely in the periphery. CONCLUSION: The increased range of relative legibility for letter targets in the peripheral retina underscores the importance of using letter-by-letter scoring to obtain precise measures of visual acuity in patients without central vision.

Adult↗

PubMed1995

Perceptual learning in parafoveal vision.

The present study tests the effects of practice on parafoveal vernier and resolution acuity. By measuring task specificity, transfer of training to other retinal locations in the trained eye and transfer of training to the untrained eye, we directly address whether improvement on these tasks is the result of changes in the underlying physiological processes or simply the development of new cognitive strategies. We found that: (1) significant learning can occur for both vernier and resolution acuity in many (but not all) individuals; (2) there were significant individual differences in the degree and time-course of learning: (3) learning transfers to the untrained task; and (4) learning transfers to the other eye particularly when the visual pathway leads to the trained hemisphere. These results suggest that both physiological and cognitive processes contribute to the improvement seen after repetitive practice on these visual tasks.

Adolescent↗

PubMed1995

Field of view and equivalent viewing power of near-vision telescopes.

There are often substantial differences in linear field of view (FOV) and equivalent viewing power (EVP) when a distance telescope is either fitted with an objective lens cap or adjusted in length to focus for near vision. In addition, larger differences in linear FOV are found for Galilean than for Keplerian telescopes of similar magnification and EVP. Simple formulas are presented here that make use of EVP as a factor for calculating the linear FOV ratio between the two methods of converting distance Galilean and Keplerian telescopes for near vision. Examples are provided to illustrate the clinical application of these formulas. The information presented here may be helpful when making recommendations concerning the most appropriate method of converting a telescope for near vision.

Humans↗

PubMed1991

Adjustable focus telescopes for near vision.

It is important for clinicians to know the equivalent viewing power and corresponding equivalent viewing distance of the adjustable-focus telescopes they prescribe for low vision patients. Formulas are presented here to calculate the equivalent viewing power and distance of these telescopes. The optical effects of adjusting a telescope for near vision are discussed and compared to using a lens cap fitted on the objective to permit focusing on a near target. Commonly prescribed adjustable-focus telescopes of four representative magnifications were evaluated. The results are presented in the form of a nomogram which can be used for determining the equivalent viewing distance of these telescopes based on the front vertex focal distance of the focused device. Other considerations including sources of error and field of view are also addressed.

Eyeglasses↗