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PubMedDate not supplied

Effects of soft-start irradiation on the depth of cure and marginal adaptation to dentin.

Marginal adaptation of four resin composites, Clearfil APX, Estelite, Silux Plus and Z-100 cured with two irradiation methods (soft-start or high-power start) of a commercial soft-start halogen lamp unit (Elipar Highlight) were evaluated by measurement of the wall-to-wall contraction gap width. One-hundred and sixty cylindrical cavities, 3 mm in diameter and 1.5 mm in depth, were prepared in extracted human molars. The 80 cavity walls were treated with the Megabond system and each 20 cavities were filled with one of four resin composites. Then, each 10 fillings were irradiated by the soft-start method (soft-power light for 10 seconds followed by high-power light for 30 seconds) or high-power light for 40 seconds. The other 80 cavity walls were treated with an experimental bonding system consisting of 0.5M EDTA as a conditioner, 35% glyceryl mono-methacrylate as a primer and Clearfil Photo Bond as a bonding agent. The cavities were restored wtih the four resin composites and two irradiation methods, the same as the Megabond group. The contraction gap was measured with a light microscope and expressed in % of the cavity diameter. In addition, the curing capability of these two light sources was evaluated by measurement of the curing depth of the four resin composites using a split Teflon mold 4 mm in inner-diameter and 8 mm in height. Marginal gap formation of Clearfil APX, Estelite and Silux Plus with the experimental bonding system was completely prevented regardless of the kind of irradiation methods used. The deterioration of marginal adaptation caused by the Megabond system could not be improved by use of the soft-start method programmed in Elipar Highlight.

Composite Resins↗
PubMed2006

The pursuit theory of motion parallax.

Although motion parallax is closely associated with observer head movement, the underlying neural mechanism appears to rely on a pursuit-like eye movement signal to disambiguate perceived depth sign from the ambiguous retinal motion information [Naji, J. J., & Freeman, T. C. A. (2004). Perceiving depth order during pursuit eye movement. Vision Research, 44, 3025-3034; Nawrot, M. (2003). Eye movements provide the extra-retinal signal required for the perception of depth from motion parallax. Vision Research, 43, 1553-1562]. Here, we outline the evidence for a pursuit signal in motion parallax and propose a simple neural network model for how the pursuit theory of motion parallax might function within the visual system. The first experiment demonstrates the crucial role that an extra-retinal pursuit signal plays in the unambiguous perception of depth from motion parallax. The second experiment demonstrates that identical head movements can generate opposite depth percepts, and even ambiguous percepts, when the pursuit signal is altered. The pursuit theory of motion parallax provides a parsimonious explanation for all of these observations.

Computer Peripherals↗
PubMed1984

Sensory modalities in depth perception by golden hamsters.

Golden hamsters are able to detect differences in the height of a platform from which they jump, as measured by their increasing latencies prior to jumping from increased elevations. This ability is very effective when optical information is available, but it is also present when hamsters jump in total darkness. A second experiment shows that, when hamsters are placed on a real physical cliff, they preferentially use tactile information over visual information to guide their choice of the side from which to descend. In a nonvisual setting, tactile stimulation is used in conjunction with other types of cues. Evidence is provided to suggest that these cues are of an acoustical nature.

Animals↗
PubMed1980

Spatial properties of visual fixation neurons in posterior parietal association cortex of the monkey.

1. A systematic study of the positional selectivity of visual fixation (VF) neurons of the posterior parietal association cortex (area 7a or PG) was made in seven hemispheres of four alert behaving monkeys. By gaze fixation on a small spot of light in space, 125 units were identified as VF neurons. the position of the fixation target was varied not only in the frontal plane, but also in depth. 2. Microelectrode penetrations were made in the anterior and posterior part of area 7a. The recording sites of 104 VF neurons, determined histologically, were distributed mainly in the posterior part: the caudal part of the posterior bank of the intraparietal sulcus and the caudal third of the anterior bank of the superior temporal sulcus. The following conclusions are based mainly on the observations of the VF neurons in the posterior part of area 7a. 3. Most of the VF neurons examined in the frontal plane (86/93) had a preferred direction of gaze along the horizontal (39/86), vertical (38/86), or diagonal axis (9/86), and their discharge rates were monotonic increasing functions of the angle of deviation from the center. 4. Many VF neurons had selectivity in the depth of fixation. The majority (41/63) were activated more intensely when the fixation point was nearer to the animal (less than 50 cm), whereas a considerable number (18/63) were activated better when the fixation point was further from the animal (100 cm or more). There were a few units (4/63) that discharged maximally at intermediate distances. 5. Thirty-two VF neurons were studied in detail along all three axes: vertical, horizontal, and depth. About half of them (17/32) were found to be selective both in the radial direction and the distance of fixation, while the others displayed selectivity in the direction of gaze alone (11/32) or in depth alone (4/32). 6. The activity of VF neurosis in the dark was compared to that in a lighted room in order to examine their relationship to eye position in detail. Half of the VF neurons tested (25/50) showed almost the same discharge rate in the dark as in the lighted room in spite of the absence of visual stimuli other than the target light in the fovea. Moreover, the discharge rate of the majority of these VF neurons displayed a close correlation with eye position, even in complete darkness. On the other hand nearly half of the VF neurons (22/50) showed a decrease in discharge rate in the dark during fixation at preferred positions suggesting that visual stimuli in the surroundings have some excitatory effects on these neurons. There were also some VF neurons whose activity decreased when the target light was interrputed. Even in such visually sensitive VF neurons, their positional selectivity depended mainly on eye position. 7...

Animals↗
PubMed1975

Visual parameters associated with recovered retrobulbar optic neuritis.

Visual acuity, color vision, pupillary reaction, induced Pulfrich phenomenon, kinetic fields, static fields, afterimage testing, and ophthalmoscopic evaluation were studied in nine patients with a history of retrobulbar neuritis. The most consistently reliable test for determining the presence of an old optic nerve defect in these patients was meridional 0 to 180 degrees static perimetry. There was a uniform decrease in brightness discrimination to either side of the foveal peak.

Accommodation, Ocular↗
PubMed2003

Spatial summation of S-cone ON and OFF signals: effects of retinal eccentricity.

We studied spatial summation for S-cone ON and OFF signals as a function of retinal eccentricity in human subjects. S-cone isolation was obtained by the two-colour threshold method of Stiles, modified by adding blue light to the yellow background. Test stimuli were blue light increments or decrements within a circular area of variable size. These were presented for 100 ms at 0 to 20 deg along the horizontal temporal retinal meridian. Ricco's area of complete spatial summation was measured from the threshold vs. area curves. This was nearly constant and approximately the same for both types of stimuli within the 0-5 deg range and increased beyond this range. The decremental area increased faster, suggesting that separate mechanisms, presumably ON and OFF, integrate S-cone increments and decrements. The results appear to provide new evidence for the existence of separate S-cone ON and OFF pathways. We compare the data with known morphology of primate retina and assume that, if S-cone decrements are detected via separate OFF cells, these should differ in density and dendritic field size from the S-cone ON cells, but only in the retinal periphery.

Adult↗
PubMed2006

Changes in the refractive state during prey capture under low light in the nocturnal cardinalfish Apogon annularis.

Many nocturnal and crepuscular fish use vision to feed and function under low light levels. However, little is known about their ability to accommodate or their visual acuity under these light levels. We used Infrared Photoretinoscopy to track the refractive state of the eye during prey capture under low light in Apogon annularis, a nocturnal reef fish. Anatomical measurements of the eyes allowed calculations of visual acuity. Changes in the refractive state were observed in approximately 75% of the prey capturing strikes, preceding the strikes by 30 ms. These changes were rare between strikes or when prey was absent. Anatomical measurements indicated that the number of photo-detection units in a retinal image greatly exceeded the minimal number needed to detect prey. We conclude that nocturnal vision in A. annularis is sufficiently sensitive to allow accommodation during prey capture.

Accommodation, Ocular↗
PubMed2001

The ChromaGen contact lens system: colour vision test results and subjective responses.

The ChromaGen lens system is designed to enhance colour perception in colour vision deficiency (CVD). To investigate its efficacy, 14 CVD subjects were prescribed ChromaGen contact lenses. Colour vision tests (Ishihara, Farnsworth Munsell D-15, Farnsworth Lantern) were administered at baseline, lens dispensing, and after a 2-week lens-wearing trial during which subjective responses were recorded daily using visual analogue scales. ChromaGen lenses significantly reduced ishihara error rates (p < 0.001; ANOVA), particularly for deutan subjects. There was also a significant reduction in errors (p < 0.005) on the D-15 test. Conversely, lens wear had no significant effect on Farnsworth Lantern test performance. Subjectively, subjects reported enhanced colour perception, but poor vision in dim light. Judgement of distance and motion were only slightly affected. We conclude that ChromaGen lenses may enhance subjective colour experience and assist in certain colour-related tasks, but are not indicated as an aid for CVD in occupations with colour vision-related restrictions.

Adolescent↗
PubMed1989

Development of infant reaching in the dark to luminous objects and 'invisible sounds'.

Two studies were conducted to investigate the existence of an unusual U-shaped developmental function described by Wishart et al (1978) for human infants reaching towards invisible sounds. In study 1, 2-7 month olds were presented with four conditions: (i) an invisible auditory stimulus alone, (ii) a glowing visual stimulus alone, (iii) auditory and visual stimuli on the same side (ie combined), and (iv) auditory and visual stimuli on opposite sides (ie in conflict). Study 2 was designed to examine the effects of practice and possible associations made when using the 'combined conflict' paradigm. Infants of 5 and 7 months of age were given five trials with the auditory stimulus, with or without prior visual experience, and five trials with the visual stimulus, with the position of the stimulus varied on each trial. Stimuli were presented individually at the midline, and +/- 30 and +/- 60 degrees from the midline. In both studies testing was conducted in complete darkness. Results indicated that the auditory-alone condition was slower to elicit a reach from the infants, relative to the visual-alone one, and reaches were least frequent to the auditory target. No U-shaped function was obtained, and reaching for auditory targets occurred later in age than for visual targets, but even at 7 months of age did not occur as often and was achieved by fewer infants. In both studies the quality of the reach was significantly poorer to auditory than to visual targets, but there were some accurate reaches. This research adds to our understanding of the development of auditory-manual coordination in sighted infants and is relevant to theories of auditory localization, visually guided reaching, and programming for the blind.

Attention↗