The Development of Crowding and Interocular Interactions in a Resolution Acuity Task

Purpose.: To investigate the impact of interocular similarities of a surround stimulus on foveal resolution acuity in the normally developing visual system. Methods.: Liquid crystal shutter goggles synchronized with the monitor frame rate were used to present a Landolt C and surround bars to one or both eyes, in monocular, dichoptic, half-binocular, and binocular viewing conditions. Resolution acuity was measured under each condition in 56 normally sighted children (7 to 14 years of age) and 22 adults (21 to 38 years of age). The effect of the surround bars (crowding) was tested in a subgroup of nine children, and 10 adults. Results.: Across all age groups resolution acuity was significantly better in the binocular condition than in the other three viewing conditions (binocular summation), and was significantly better in the half-binocular (with target presented to the test eye and bars presented to both eyes) than in the dichoptic condition (target presented to test eye and bars presented to the nontested eye only). In children, but not in adults, resolution acuity was significantly better without than with bars. Conclusions.: The interocular similarities may explain the better visual resolution in the half-binocular condition than in the dichoptic condition for all age groups tested. The results suggest that interocular interactions underpinning resolution acuity under these viewing conditions are developed in early childhood. The foveal crowding effect was found to be apparent at the beginning of school age, and diminished with maturation

Negligible impact on posture from 5-diopter vertical yoked prisms

PURPOSE: Yoked prisms are used by some optometrists to adjust posture, but evidence to support this practice is sparse and low level. The aim of this research was to investigate whether vertical yoked prisms have an impact on posture in healthy adults. METHODS: Posture was assessed objectively in 20 healthy adults, by recording a range of joint angles or body segment locations at the ankle, hip, torso, neck, and head during participant observation of a straight-ahead target, and subsequently with eyes closed. Recording occurred before, during, and after wearing goggles with control plano lenses, and 5-diopter (D) base-up and 5-D base-down yoked prisms. In each viewing condition, the goggles were worn for 30 minutes. Interaction effects of lens/prism condition by time on joint angles and body orientation were determined. RESULTS: In the eyes-open and eyes-closed conditions, no significant lens/prism × time interaction effects were found at the torso, neck, hip, or ankle (P > 0.1). However, in both eyes-open and eyes-closed conditions a significant lens/prism × time interaction was found at the head (P = 0.031 and 0.006, respectively), with head extended (tilted backward) by up to 2.5 degrees more while viewing with base-down prisms than with plano lenses. CONCLUSIONS: In healthy adults, 5-D base-down yoked prisms were not associated with a change in body posture. A small effect on head orientation and not at other locations suggests a minimal effect on posture. Research in a larger sample and in individuals with abnormal posture is needed to verify this

Enhancement of Resolution Acuity in a Half-Binocular Viewing Condition

Purpose.: To investigate the effect of interocular stimulus similarity on foveal resolution acuity. Methods.: Liquid crystal shutter goggles synchronized with the monitor refresh rate were used to present a Landolt C and surround bars to one or both eyes, in four viewing conditions (monocular, dichoptic, half-binocular, and binocular). Resolution acuity was measured in each condition in 22 normally sighted adults. Results.: Resolution acuity was significantly better in the binocular condition than in the other three viewing conditions (binocular summation) and was significantly better in the half-binocular condition (with target presented to the test eye and bars presented to both eyes) than in the dichoptic condition (target presented to the test eye and bars presented to the nontested eye only). Conclusions.: Monocular resolution acuity depends in part on interocular similarities of the stimulus surrounding the central target. This finding may have implications in the design of stimuli for vision-training therapies

Accelerated settling of particulate matter by ’marine snow’ aggregates

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution December 1985Samples from time-series sediment traps deployed in three distinct oceanographic settings (North Pacific, Panama Basin, and Black Sea) provide strong evidence for rapid settling of marine particles by aggregates. Particle water column residence times were determined by measuring the time lag between the interception of a flux event in a shallow trap and the interception of the same event in a deeper trap at the same site. Effective sinking speeds were determined by dividing the vertical offset of the traps (meters) by the interception lag time (days). At station Papa in the North Pacific, all particles settle at 175 m day-1, regardless of their composition, indicating that all types of material may be settling in common packages. Evidence from the other two sites (Panama Basin and Black Sea) shows that particle transport may be vertical, lateral, or a combination of directions, with much of the Black Sea flux signal being dominated by lateral input. In order to ascertain whether marine snow aggregates represent viable transport packages, surveys were conducted of the abundance of these aggregates at several stations in the eastern North Atlantic and Panama Basin using a photographic technique. Marine snow aggregates were found in concentrations ranging from ~1 mm3 liter-1 to more than 500 mm3 liter-1. In open ocean environments, abundances are higher near the surface (production) and decline with depth (decomposition). However, in areas near sources of deep input of resuspended material, concentrations reach mid-water maxima, reflecting lateral transport. A model is proposed to relate the observed aggregate abundances, time series sediment flux and inferred circulation. In this model, depthwise variations in sediment flux and aggregate abundance result from suspension from the sea floor and lateral transport of suspended aggregates which were produced or modified on the sea floor. Temporal changes in sediment flux result from variations in the input of fast-sinking material which falls from the surface, intercepts the suspended aggregates, and transports them to the sea floor. A new combination sediment trap and camera system was built and deployed in the Panama Basin with the intent of measuring the flux of marine snow aggregates. This device consists of a cylindrical tube which is open at the top and sealed at the bottom by a clear plate. Material lying on the bottom plate is illuminated by strobe lights mounted in the wall of the cylinder and photographed by a camera which is positioned below the bottom plate. Flux is determined as the number of aggregates arriving during the time interval between photographic frames (# area-1 time-1). Results show that essentially all material arrives in the form of aggregates with minor contributions of fecal pellets and solitary particles. Sinking speeds (m day-1), calculated by dividing the flux of aggregates (# m-2 day-1) by their abundance (# m-3), indicate that the larger (4-5mm) aggregates are flocculent and sink slowly (~1m day-1) while the smaller aggregates (1-2.5mm) are more compact and sink more quickly (~36m day-1). These large, slow-sinking aggregates may have been re-suspended from the sediment water interface at nearby basin margins.This research was supported by ONR contract numbers N00014-82-C-0019 and N00014-85-C-0001, NSF grant numbers OCE-83-09024, OCE-84-17106, and DPP-85-01152 and the WHO1 education office

Variations In the Abundance and Distribution of Aggregates In the Ross Sea, Antarctica

The vertical distribution and temporal changes in aggregate abundance and sizes were measured in the Ross Sea, Antarctica between 2002 and 2005 to acquire a more complete understanding of the mechanisms and rates of carbon export from the euphotic layer. Aggregate abundance was determined by photographic techniques, and water column parameters (temperature, salinity, fluorescence, transmissometry) were assessed from CTD profiles. During the first three years the numbers of aggregates increased seasonally, being much more abundant within the upper 200 m in late summer than in early summer from 50 to 100 m (12.5 L–1 in early summer vs. 42.9 L–1 in late summer). In Year 4 aggregate numbers were substantially greater than in other years, and average aggregate abundance was maximal in early rather than late summer (177 vs. 84.5 L–1), which we attributed to the maximum biomass and aggregate formation being reached earlier than in other years. The contribution of aggregate particulate organic carbon to the total particulate carbon pool was estimated to be 20%. Ghost colonies, collapsed colonies of the haptophyte Phaeocystis antarctica, were observed during late summer in Year 4, with maximum numbers in the upper 100 m of ca. 40 L–1. Aggregate abundance, particulate organic carbon and ghost colonies all decreased exponentially with depth, and the rate of ghost colony disappearance suggested that their contribution to sedimentary input was small at the time of sampling. Bottom nepheloid layers were commonly observed in late summer in both transmissometer and aggregate data. Late summer nepheloid layers had fluorescent material within them, suggesting that the particles were likely generated during the same growing season. Longer studies encompassing the entire production season would be useful in further elucidating the role of these aggregates in the carbon cycle of these regions

Time Series Measurements of Chlorophyll Fluorescence in the Oceanic Bottom Boundary Layer With a Multisensor Fiber-Optic Fluorometer

An in situ multisensor fiber-optic fluorometer (MFF) has been developed to acquire long-term chlorophyll fluorescence measurements in the oceanic bottom boundary layer to characterize the finescale pigment structure at vertical spatial scales comparable to physical measurements. The eight fluorescence sensors of the MFF are composed of dual optical fibers of varying lengths (1.5-8 m), with the fiber ends oriented at 30 degrees to each other and enclosed by a small light baffle. Strobe excitation blue light is passed through one of each pair of optical fibers and stimulated chlorophyll fluorescence is carried back to a photomultiplier. Two sets of four fluorescence sensors assigned to high- and low-sensitivity photomultiplier detectors enable chlorophyll a measurements in two ranges, 0-50 mg m(-3) and 0-200 mg m(-3), respectively. Aspects of the design of the fiber-optic sensor are described that were intended to optimize detection of fluorescence signals and minimize interference by ambient light. The fiber-optic sensor outputs were stable with minimal instrument drift during long-term field operations, and measurements were not affected by turbidity and ambient light. A vertical array of fiber-optic fluorescence sensors supported on a tripod has been deployed at coastal sites for up to seven weeks and chlorophyll fluorescence was obtained with sufficiently high vertical spatial and temporal resolution