Temporal development of photorefractive solitons up to telecommunication wavelengths in strontium-barium niobate waveguides.

We experimentally investigate the temporal development of photorefractive solitons in strontium-barium niobate waveguides at visible and infrared wavelengths. The development times in the infrared are shown to be comparable with those in the visible. The results are compared with predictions of a previously published model.

Dimerization of the Epstein-Barr virus ZEBRA protein in the yeast two-hybrid system. Comparison Of a ZEBRA variant with the B95-8 form.

Epstein-Barr virus (EBV) is a herpes virus associated with several human tumors. The EBV protein, ZEBRA, is a transactivator of the basic leucine zipper family (bZip). It binds to specific sequences on DNA and is able to interact with cellular proteins such as p53. The interaction of the ZEBRA protein with its cognate DNA sequences is stable as long as the dimerization domain is functional. Recent work from this laboratory identified a ZEBRA variant (Z206) with a single amino acid change at residue 206. An alanine is substituted for a serine, and this replacement is present in 72% of nasopharyngeal carcinoma from Europe and North Africa. As amino acid 206 lies within the dimerization domain it could be instrumental in interactions with other proteins. The yeast two-hybrid system was used to study ZEBRA-protein interactions. As ZEBRA by itself is a transactivator in yeast, it cannot be used directly in this assay. This paper describes modifications in ZEBRA amino acid sequences, rendering it usable in the yeast two-hybrid assay. We compared the dimerization capacity of the Z206 variant to that of ZEBRA from B95-8 (Z95) and observed that reporter gene activity with Z206 was consistently lower than that of Z95 (P < 0.05). Furthermore, no interaction was found to occur between either form of ZEBRA (Z206 or Z95) and the tumor suppressor, p53 in the yeast two-hybrid system.

Observation of bright spatial photorefractive solitons in a planar strontium barium niobate waveguide.

We have obtained stationary bright spatial solitons in a planar photorefractive strontium barium niobate waveguide for visible light ranging from 514.5 to 780 nm. Even for larger wavelengths (lambda=1047 nm) strong self-focusing of the beam was observed; however, input power had to be some orders of magnitude higher than for visible light for self-focusing to occur. Furthermore, we found transient self-trapping of red light (lambda=632.8 nm) that corresponds to the formation of bright quasi-steady-state solitons.

Color perception within a chromatic context: the effect of short-wavelength light on color appearance.

Light at the boundary of a uniform test field (contrast) has a qualitatively different effect on color perception than light in more remote noncontiguous regions (context). Basic properties of color perception with contextual short-wavelength light are assessed here with a 1 degree test field surrounded by either contiguous or noncontiguous 440 or 491 nm light (32 td). Contrasting stimuli are 3 or 5 degrees adapting fields, a thin 1 degree i.d.-2 degrees o.d. (0.5 degree wide) contiguous band, or a large 1 degree i.d.-5 degrees o.d. contiguous surround. Contextual stimuli are a remote 3 degrees i.d.-5 degrees o.d. ring or 0.5 degree wide noncontiguous bands at various distances from the edge of the 1 degree test field (2 degrees i.d.-3 degrees o.d., 3 degrees i.d.-4 degrees o.d., or 4 degrees i.d.-5 degrees o.d. bands). Contiguous surrounds have little influence on color appearance, but remote noncontiguous short-wavelength light strong affects the color of the test field, shifting it toward redness. The shift toward redness increases as a thin 440 nm band is moved farther from the test field (up to 5 degrees), unlike the effect of distance on remote middle- and long-wavelength bands. Measurements comparing the effects of 440 nm and luminance-equated 491 nm light indicate a contribution from S cones.

Color perception within a chromatic context: changes in red/green equilibria caused by noncontiguous light.

We measured changes in the color appearance of one light caused by another light presented in a well-separated region. Observers viewed a 1 degrees test field superimposed on a 3 degrees, 540 or 660 nm adapting field (32 or 320 td). The change in appearance due to noncontiguous light was determined by surrounding the 3 degrees adapting field with a continguous 3 degrees i.d., 5 degrees o.d. ring of either 32 or 320 td. The ring was 540, 660 nm or achromatic (tungsten-halogen "white"). The test was an admixture of 549 and 660 nm light, and varied from 6 to 1000 td. The observer adjusted the ratio of 549 to 660 nm test light so the test appeared neither reddish nor greenish. A 540 or 660 nm ring had a chromatic inducing effect on the small test that mimicked a simple surround contiguous with the test. Results with an achromatic ring were more complex: an isolated achromatic ring (no adapting field present) had virtually no effect on the color appearance of the test, but the same achromatic ring surrounding a chromatic adapting field shifted the test toward the color appearance of the adapting light (e.g. introducing a "white" ring surrounding a "green" adapting field shifted the test toward greenness). A thin pencil-width band of "white" light superimposed on a larger 5 degrees adapting field had an effect similar to a "white" 3-5 degrees ring. These results demonstrate (1) strong effects of the remote noncontiguous lights and (2) that the change in color appearance they cause is not a simple function of only the light in the noncontinguous region. The change depends on other lights in view. The visual processes revealed in these experiments are considered in terms of inferred illumination and surface reflectances of objects in natural scenes.

Foveal cone detection statistics in color-normals and dichromats.

We measured for six male observers, the psychometric functions for the detection of two simultaneously presented points of light. The test stimuli were two 1 min point sources separated by 17 min arc, and pulsed for 0.5 msec. The stimuli varied in wavelength from 500 to 620 nm. The psychometric functions were fit with a model that assumes ideal detection and the following properties: (1) Poisson-distributed quantal absorptions; (2) binomial sampling of foveal long-wavelength-sensitive (LWS) and middle-wavelength-sensitive (MWS) cones; (3) independent responses of the LWS and MWS cones; and (4) the Smith-Pokorny fundamentals for cone spectral sensitivities. Based on chi 2 fits to the psychometric functions for detecting neither, one or both of the two-point stimuli presented, estimates were derived for the minimum quantal catch by a single cone for detection (C), the number of effective cones illuminated by a point stimulus at threshold (N) and the proportion of central foveal cones of the LWS type (PL). Three observers were color-normal, two were protanopes and one was a deuteranope. A second deuteranope was included in the design but his data were too unreliable for an unambiguous solution. The estimated quantal requirement C was consistently near 5(4-6), and the effective number of illuminated cones always was 1 or 2. The plausible range of PL (98% confidence interval) for the color-normal observers was 0.48-0.68 (observer YY), 0.76-0.90 (observer MW) and 0.77-0.95 (observer DF). The best fitting PL solution for these observers were 0.61, 0.82 and 0.88, respectively. These were comparable to the values obtained from flicker photometric data. The best PL value for each of the protanopes was 0.00 and for the deuteranope the best PL value was 0.98.

Muscarine receptor types mediating autoinhibition of acetylcholine release and sphincter contraction in the guinea-pig iris.

The potencies of several muscarine receptor antagonists in blocking either the autoinhibition of acetylcholine release or the muscarinic contraction of the sphincter muscle upon acetylcholine release were investigated in the guinea-pig iris. The agonist at pre- or postjunctional muscarine receptors was acetylcholine released upon field stimulation (5.5 Hz, 2 min) of the irides preloaded with 14C-choline. The stimulation-evoked 14C-overflow was doubled in the presence of atropine 0.1 mumol/l but unaffected by the agonist (+/-)-methacholine (50 mumol/l). Thus, under the present stimulation conditions, the autoinhibition of acetylcholine release on the guinea-pig iris cholinergic nerves was nearly maximally activated. Isotonic contractions of the irides upon field stimulation consisted of a rapid, atropine (0.1 mumol/l)-sensitive peak phase followed by a sustained contraction which involved a cholinergic and a non-cholinergic stimulation of the sphincter muscle. The M2-selective antagonists methoctramine (10 mumol/l) and gallamine (100 mumol/l) increased both the 14C-overflow and the peak contractions evoked by field stimulation. In contrast, the M3-selective antagonist hexahydrosiladifenidol (0.1-10 mumol/l) failed to affect the evoked 14C-release but concentration-dependently (1-10 mumol/l) reduced the iris contractions. Pirenzepine (10 mumol/l) enhanced the evoked 14C-overflow and inhibited the peak contractions (0.1-10 mumol/l; maximal effect at 10 mumol/l). The low potency of the antagonist at both receptor sites indicates that an M1 muscarine receptor is not involved. The results are consistent with the idea of M2 muscarine receptors mediating autoinhibition of acetylcholine release in the guinea-pig iris and M3-like receptors inducing the contraction of the sphincter muscle.

Different muscarine receptors mediate the prejunctional inhibition of [3H]-noradrenaline release in rat or guinea-pig iris and the contraction of the rabbit iris sphincter muscle.

To investigate the muscarine receptor type mediating inhibition of [3H]-noradrenaline release from the isolated rat and guinea-pig iris we have determined the potency of antimuscarinic drugs to antagonize the methacholine-induced inhibition of [3H]-noradrenaline overflow evoked by field stimulation (3 Hz, 2 min). The prejunctional apparent affinities were compared with those obtained for postjunctional muscarine receptors mediating the methacholine-induced contraction of the isolated rabbit iris sphincter muscle. Prejunctional apparent affinity constants of pirenzepine (6.67), himbacine (8.51), methoctramine (7.92), 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP, 8.00), hexahydro-difenidol enantiomers (6.92, (R); 5.77, (S)) in the rat iris and methoctramine (7.58) in the guinea-pig iris indicate the presence of M2 receptors. Although the postjunctional affinity constants in the rabbit iris sphincter of methoctramine (5.93), gallamine (3.92), and 4-DAMP (9.07) confirm our previous suggestions of the presence of M3-like receptors, the results obtained with the hexahydro-difenidol enantiomers do not agree with that concept. The postjunctional affinity constants of the hexahydro-difenidol enantiomers were not different from the prejunctional values (6.86, (R); 5.55, (S)), indicating a similar and low degree of stereoselectivity for these stereoisomers at both receptor sites (14 and 17, (R)/(S)-ratios, respectively). Hence, the postjunctional muscarine receptor in the rabbit iris sphincter fails to exhibit the high degree of stereoselectivity observed for hexahydro-difenidol enantiomers at M3 receptors on other smooth muscles.

Instrument myopia conceptions, misconceptions, and influencing factors.

The literature on instrument myopia is reviewed, with the review organized around three principal objectives. One is to describe and discuss various factors that may influence the degree to which instrument myopia is manifested, including monocular vs. binocular viewing, age, direction of focus, illumination level, fatigue, magnification, astigmatic variations, optical decentration, perceived proximity of the target and peripheral surround, and experience. The second objective is to discuss the intermediate resting state conception of accommodation, its application to instrument myopia, and its strengths and weaknesses as applied to the available literature. The third objective is to summarize the salient problems in the instrument myopia literature, and to present a set of recommendations for guiding future work.

Comparison of subjective lens preference to objective refractive error measurements in pigtail macaques.

Two measurements can be taken to determine the refractive error in human beings: a subjective, lens preference measurement and objective retinoscopy. This study determined the subjective refractive error in eight pigtailed monkeys by placing lenses of different powers in front of peepholes in a solid wall cage and recording the amount of time each subject used the holes. Retinoscopy measurements were then taken and compared to the subjective findings to determine the degree of similarity between these two refraction methods. The results showed a high correlation between the subjective measurements and the vertical ocular refraction (VOR) and spherical equivalent (SE) (rho = 0.96), further supporting generalizations made from nonhuman primate vision studies to human beings.

Overaccommodation, underaccommodation, and the clinical phoropter: a study of instrument myopia and related effects.

To explore the degree to which a phoropter can induce overaccommodation (instrument myopia) and/or underaccommodation , 19 college-age subjects participated in a series of measurements of accommodation response. Accommodation responses were assessed while subjects looked through a phoropter (both with standard 19-mm viewing apertures and through 2-mm artificial pupils) and when no phoropter was present. Subjects were tested both monocularly and binocularly, and under three stimulus conditions (near target, far target, and total darkness). Even without the phoropter , subjects tended to overaccommodate for the far target. The 19-mm phoropter produced no significant overaccommodation or underaccommodation effects over and above those observed without the presence of the phoropter . The 2-mm artificial pupils produced significantly more underaccommodation for the near target. Results indicate a tendency for accommodation response to approach an intermediate resting position as the viewing situation becomes impoverished.