Self-management, health service use and information seeking for diabetes care among recent immigrants in Toronto.

INTRODUCTION: Our objective was to explore self-management practices, health services use and information-seeking for type 2 diabetes care among adult men and women from four recent immigrant communities in Toronto. METHODS: A structured questionnaire was adapted for the Canadian context and translated into 4 languages. A total of 184 participants with type 2 diabetes-130 recent immigrants and 54 Canadian-born-were recruited in both community and hospital settings. RESULTS: Recent immigrants were significantly less likely than the Canadian-born group to perform regular blood glucose and foot checks and significantly more likely than the Canadian-born group to be non-smokers, participate in regular physical activity and reduce dietary fat. Recent immigrants were significantly less likely than the Canadian-born group to use a specialist, alternative provider and dietician and less likely to report using dieticians, nurses and diabetes organizations as sources of diabetes-related information. Important differences were observed by sex and country of origin. CONCLUSION: Findings suggest that diabetes prevention and management strategies for recent immigrants must address linguistic, financial, informational and systemic barriers to information and care.

Latency characteristics of the short-wavelength-sensitive cones and their associated pathways.

There are many distinct types of retinal ganglion and LGN cells that have opponent cone inputs and which may carry chromatic information. Of interest are the asymmetries in those LGN cells that carry S-cone signals: in S-ON cells, S+ signals are opposed by (L + M) whereas, in many S-OFF cells, L+ signals are opposed by (S + M), giving -S + L - M (C. Tailby, S. G. Solomon, & P. Lennie, 2008). However, the S-opponent pathway is traditionally modeled as +/-[S - (L + M)]. A phase lag of the S-cone signal has been inferred from psychophysical thresholds for discriminating combinations of simultaneous sinusoidal modulations along +/-[L - M] and +/-[S - (L + M)] directions (C. F. Stromeyer, R. T. Eskew, R. E. Kronauer, & L. Spillmann, 1991). We extend this experiment, measuring discrimination thresholds as a function of the phase delay between pairs of orthogonal component modulations. When one of the components isolates the tritan axis, there are phase delays at which discrimination is impossible; when neither component is aligned with the tritan axis, discrimination is possible at all delays. The data imply that the S-cone signal is delayed by approximately 12 ms relative to (L - M) responses. Given that post-receptoral mechanisms show diverse tuning around the tritan axis, we suggest that the delay arises before the S-opponent channels are constructed, possibly in the S-cones themselves.

Pacing for hypertrophic obstructive cardiomyopathy does it work?

Sixty-nine years old lady presented with sudden cardiac arrest, she was found to have hypertrophic obstructive cardiomyopathy, she refused septal myomectomy and had a dual chamber ICD implanted, she was put on right ventricular apical pacing with short AV interval, after pacing her max pressure gradient across left ventricular out flow tract (LVOT) dropped from 117 mmHg to 21 mmHg and her symptoms much improved over a follow up period of 1 year.

Erratum to "Information limitations in perception of shape from texture". [Vision Research 41 (2001) 1519-1534].

Li and Zaidi (Li, A., and Zaidi, Q. (2000) Vision Research, 40, 217-242) showed that the veridical perception of the 3-dimensional (3D) shape of a corrugated surface from texture cues is entirely dependent on the visibility of critical patterns of oriented energy. These patterns are created by perspective projection of surface markings oriented along lines of maximum 3D curvature. In images missing these orientation modulations, observers confused concavities with convexities, and leftward slants with rightward slants. In this paper, it is shown that these results were a direct consequence of the physical information conveyed by different oriented components of the texture pattern. For texture patterns consisting of single gratings of arbitrary spatial frequency and orientation, equations are derived from perspective geometry that describe the local spatial frequency and orientation for any slant at any height above and below eye level. The analysis shows that only gratings oriented within a few degrees of the axis of maximum curvature exhibit distinct patterns of orientation modulations for convex, concave, and leftward and rightward slanted portions of a corrugated surface. All other gratings exhibit patterns of frequency and orientation modulations that are distinct for curvatures on the one hand and slants on the other, but that are nearly identical for curvatures of different sign, and nearly identical for slants of different direction. The perceived shape of surfaces was measured in a 5AFC paradigm (concave, convex, leftward slant, rightward slant, and flat-frontoparallel). Observers perceived all five shapes correctly only for gratings oriented within a few degrees of the axis of maximum curvature. For all other oriented gratings, observers could distinguish curvatures from slants, but could not distinguish signs of curvature or directions of slant. These results demonstrate that human observers utilize the shape information provided by texture components along both critical and non-critical orientations.

Veridicality of three-dimensional shape perception predicted from amplitude spectra of natural textures.

We show that the amplitude spectrum of a texture pattern, regardless of its phase spectrum, can be used to predict whether the pattern will convey the veridical three-dimensional (3-D) shape of the surface on which it lies. Patterns from the Brodatz collection of natural textures were overlaid on a flat surface that was then corrugated in depth and projected in perspective. Perceived ordinal shapes, reconstructed from a series of local relative depth judgments, showed that only about a third of the patterns conveyed veridical shape. The phase structure of each pattern was then randomized. Simulated concavities and convexities were presented for both the Brodatz and the phase-randomized patterns in a global shape identification task. The concordance between the shapes perceived from the Brodatz patterns and their phase-randomized versions was 80-88%, showing that the capacity for a pattern to correctly convey concavities and convexities is independent of phase information and that the amplitude spectrum contains all the information required to determine whether a pattern will convey veridical 3-D shape. A measure of the discrete oriented energy centered on the axis of maximum curvature was successful in identifying textures that convey veridical shape.

Information limitations in perception of shape from texture.

Li and Zaidi (Li, A., and Zaidi, Q. (2000) Vision Research, 40, 217-242) showed that the veridical perception of the 3-dimensional (3D) shape of a corrugated surface from texture cues is entirely dependent on the visibility of critical patterns of oriented energy. These patterns are created by perspective projection of surface markings oriented along lines of maximum 3D curvature. In images missing these orientation modulations, observers confused concavities with convexities, and leftward slants with rightward slants. In this paper, it is shown that these results were a direct consequence of the physical information conveyed by different oriented components of the texture pattern. For texture patterns consisting of single gratings of arbitrary spatial frequency and orientation, equations are derived from perspective geometry that describe the local spatial frequency and orientation for any slant at any height above and below eye level. The analysis shows that only gratings oriented within a few degrees of the axis of maximum curvature exhibit distinct patterns of orientation modulations for convex, concave, and leftward and rightward slanted portions of a corrugated surface. All other gratings exhibit patterns of frequency and orientation modulations that are distinct for curvatures on the one hand and slants on the other, but that are nearly identical for curvatures of different sign, and nearly identical for slants of different direction. The perceived shape of surfaces was measured in a 5AFC paradigm (concave, convex, leftward slant, rightward slant, and flat-frontoparallel). Observers perceived all five shapes correctly only for gratings oriented within a few degrees of the axis of maximum curvature. For all other oriented gratings, observers could distinguish curvatures from slants, but could not distinguish signs of curvature or directions of slant. These results demonstrate that human observers utilize the shape information provided by texture components along both critical and non-critical orientations.

Motion energy versus position tracking: spatial, temporal, and chromatic parameters.

The fundamental question in motion perception is whether motion is an interpretation imposed on an object or feature perceived at separate positions at sequential instants, or whether it is the response of direction-sensitive detectors that can extract the motion-energy in the stimulus, i.e. the orientation of spatio-temporal energy. To answer this question we constructed stimuli whose position changed in one direction while the motion energy contained in the same spatial frequency moved in the same or the opposite direction (by superimposing moving sinusoidal gratings on stationary gratings of the same spatial frequency and orientation). In every case tested (0.25-25 Hz temporal frequency; 0.25-1.0 cyc/deg spatial frequency; achromatic and equiluminant contrast), the perceived direction of motion was in the direction of motion energy, indicating the existence of neurons which compute motion direction without explicitly computing spatial position. The measurements also confirmed that motion-energy computations can be modeled as separable in spatial and temporal frequency.

Perception of three-dimensional shape from texture is based on patterns of oriented energy.

This paper presents empirical support for a new observer model of inferring three-dimensional shape from monocular texture cues. By measuring observers' abilities to estimate the relative three-dimensional curvature along a textured surface from two-dimensional projected images, and concurrently examining the local spectral changes occurring in the projected image for various texture patterns, we have found that correlated changes in oriented energy along lines corresponding to the lines of maximum and minimum curvature of the surface are crucial for conveying the three-dimensional shape of the surface. Energy along these lines of maximum and minimum curvature can be used to compute the orientation of local surface patches. Texture patterns consisting of simple and complex sinusoidal gratings and plaids, and filtered noise were drawn onto a surface that was corrugated sinusoidally in depth about the horizontal axis and projected in perspective onto an image plane. The perceived relative surface curvature was reconstructed from measurements of local ordinal depth around a central fixation point at 12 different phases of the corrugation. Our results show that: (1) it is neither necessary nor sufficient to identify individual texture elements or texture gradients in order to extract the shape of the surface; (2) one-dimensional frequency modulation is insufficient for conveying complex three-dimensional shape. (3) Veridical ordinal depth is seen only when the projected pattern contains changes in oriented energy along lines corresponding to projected lines of maximum curvature of the surface. (4) For a surface corrugated in depth about the horizontal axis, this pattern of oriented energy arises from energy along the vertical direction in the global Fourier transform of the pre-corrugated pattern. (5) Local orientation changes across lines of minimum curvature can be also critical for conveying shape. (6) These correlated orientation changes along lines of maximum and minimum curvature are entirely lost in parallel projection. Hence texture is a useful cue for shape if the image is a perspective projection. (7) Only some natural textures will provide sufficient monocular cues to support veridical shape inferences, and this can be predicted from their global Fourier transforms.

Perceptual assumptions and projective distortions in a three-dimensional shape illusion.

We examine a shape illusion, in which the balconies of a building appear to tilt up or down, depending on the viewpoint. The balconies are actually level parallelogram shapes, but appear as tilted rectangles. We measured the illusory tilts observed when parallelogram shapes are viewed above the line of sight, using three-dimensional stimuli consisting of parallelograms of various tilts viewed at different orientations. Under perspective projection, parallelism and orthogonality are not preserved. However, perspective distortions alone cannot account for the perceived tilts measured in these experiments, since observers perceived illusory tilts even for stimuli in the frontoparallel plane. We introduce a model, based on the theory that observers assume ambiguously projected three-dimensional angles to be equal to 90 degrees, but revise their predictions on the basis of observation. In the model, perceived tilt is predicted as a weighted sum of the tilts predicted by the assumptions that the shape is rectangular, and that the shape is level (i.e. that the angle between the shape and the vertical backboard is equal to 90 degrees). We prove that it is mathematically impossible for a planar rectangle to share a projection with a nonrectangular parallelogram. A less restrictive assumption that just the two leading internal angles are equal to 90 degrees is suggested as an alternative, and it is further proven that this new configuration of angles leads to a unique perceived tilt. The relative weights in the model reflect the amount that each prediction is revised, and are shown to vary systematically with stimulus orientation. For some observers a better fit was found by replacing the level-tilt assumptions with an assumption that physical tilt was equal to the projected tilt.

Identification of illuminant and object colors: heuristic-based algorithms.

In everyday scenes, from perceived colors of objects and terrains, observers can simultaneously identify objects across illuminants and identify the nature of the light, e.g., as sunlight or cloudy. As a formal problem, identifying objects and illuminants from the color information provided by sensor responses is underdetermined. It is shown how the problem can be simplified considerably by the empirical result that chromaticities of sets of objects under one illuminant are approximately affine transformations of the chromaticities under spectrally different illuminants. Algorithms that use the affine nature of the correlation as a heuristic can identify objects of identical spectral reflectance across scenes lit simultaneously or successively by different illuminants. The relative chromaticities of the illuminants are estimated as part of the computation. Because information about objects and illuminants is useful in many different tasks, it would be more advantageous for the visual system to use such algorithms to extract both sorts of information from retinal signals than to discount either automatically at an early neural stage.

Adaptation to textured chromatic fields.

Probe-flash threshold curves were used to show that adaptation to textured fields consists not only of adaptation to the steady local constituents but also of a process that is similar to habituation to prolonged temporal modulation, which in this case could be caused by miniature eye movements across element boundaries. The response curves derived from probe-flash thresholds are compressive on both sides of the adaptation level after adaptation to spatially uniform fields but have an accelerating form when they are measured after adaptation to textured backgrounds. This change is suggestive of a response equalization process, which modifies the response function of each mechanism to match the cumulative frequency distribution of its inputs.

Rigid objects that appear to bend.

Simple rigid objects are presented that appear to bend when viewed from certain angles. These illusions illustrate that perspective information is used by the stereo system, that projective distortions can override rigidity constraints in motion perception, and that touch only corrects the illusion for a local region.

Decorrelation of L- and M-cone signals.

For a large sample of broadband lights reflected from natural and man-made objects, the correlation between L- and M-cone absorptions was found to be 0.99. The correlation between L + M and L - M signals was 0.21. The early recombination of cone signals in the visual system thus leads to a substantial decorrelation.

Color constancy in variegated scenes: role of low-level mechanisms in discounting illumination changes.

For a visual system to possess color constancy across varying illumination, chromatic signals from a scene must remain constant at some neural stage. We found that photoreceptor and opponent-color signals from a large sample of natural and man-made objects under one kind of natural daylight were almost perfectly correlated with the signals from those objects under every other spectrally different phase of daylight. Consequently, in scenes consisting of many objects, the effect of illumination changes on specific color mechanisms can be simulated by shifting all chromaticities by an additive or multiplicative constant along a theoretical axis. When the effect of the illuminant change was restricted to specific color mechanisms, thresholds for detecting a change in the colors in a scene were significantly elevated in the presence of spatial variations along the same chromatic axis as the simulated chromaticity shift. In a variegated scene, correlations between spatially local chromatic signals across illuminants, and the desensitization caused by eye movements across spatial variations, help the visual system to attenuate the perceptual effects that are due to changes in illumination.

Surround effects on the shape of the temporal contrast-sensitivity function.

The shape of the temporal contrast-sensitivity function at low temporal frequencies is sensitive to the relative luminance of the test and the surround. We show that this effect is due to greater sensitivity, in different conditions, either to the internal luminance modulation in the test or to temporal changes in the spatial contrast at the edge of the test. We measured temporal contrast sensitivity in tests at various luminance levels combined with surrounds at levels of higher, lower, or equal luminance as the test; compared the sensitivity for contrast modulation to luminance modulation at different temporal frequencies; and compared temporal contrast sensitivity in uniform and textured surround of equal mean luminance. Temporal contrast sensitivity was similar on equiluminant steady and out-of-phase modulating surrounds, indicating that the measured sensitivity for small tests in equiluminant surrounds is based on the detection of the temporal modulation of the spatial contrast at the edge of the test field. For all temporal frequencies, contrast sensitivity decreased as a monotonic function of the absolute magnitude of the Michelson contrast between test and surround. When small test fields of moderate to high intensities are embedded in dark surrounds, the sensitivity at lower spatial frequencies is similar to the sensitivities measured for a large test and may reflect sensitivity for luminance modulation within the test.

Comparison between spatial interactions in perceived contrast and perceived brightness.

We examined the spatial integration of simultaneously induced achromatic contrast and compared it to the spatial integration of simultaneously induced brightness. This study extends the work of Zaidi et al. [(1992). Vision Research, 32, pp. 1695-1707], who showed that the total magnitude of induced brightness can be described as the weighted sum of the brightness induced by individual elements of the surround. The results show that contrast induction, though weaker than brightness induction, occurs over greater distances, and that a weighted spatial summation model for contrast induction requires an additional static non-linear compression, which is not required to model brightness induction. The analysis indicates that the contrast compression occurs prior to the lateral interactions that generate induced contrast.

Induced effects of backgrounds and foregrounds in three-dimensional configurations: the role of T-junctions.

In three-dimensional configurations, and two-dimensional pictures of such configurations, simultaneous contrast induction from proximate backgrounds affects perceived brightness, color, and internal contrast to a greater extent than induction from coplanar or occluding surrounds or from more distant backgrounds. In the projected image the presence of occluding flanks or retinally adjacent distant backgrounds is indicated by T-junctions. However, the presence of T-junctions inhibits induced contrast irrespective of the three-dimensional percept. The configurations in this paper refute the notions that perceived coplanarity or perceptual belonging necessarily enhance induced contrast.

New configurational effects on perceived contrast and brightness: second-order White's effects.

Novel phenomena of perceived contrast and brightness in spatial configurations are presented, which are of the type used by White but consist exclusively of contrast variations or of combined contrast and luminance variations. As with White's effect, perceived contrast and brightness in these displays do not correspond to predictions based on low-level mechanisms of contrast and brightness induction, and it is suggested that spatial organisation influences the appearance of first-order and second-order stimuli in a similar fashion.

The enhanced S cone syndrome: an analysis of receptoral and post-receptoral changes.

The purpose of the study was to test the hypothesis that the retinae of patients with enhanced S cone syndrome (ESCS) have more S cones than the normal retina and these cones have replaced some of the L and M cones. Standard and spectral full-field electroretinograms, measurements of L, M, and S cone system sensitivities and S cone acuity were obtained from three patients with ESCS. The results were qualitatively consistent with the presence of more S cones and more S cone ganglion cells. To test this hypothesis further, a model of the receptoral and post-receptoral components of the S cone system was used in conjunction with psychophysical measurements of S cone system sensitivity under flashed and steady-state adaptation conditions. Within the context of the model, the data were consistent with an increase in the number of S cones and S - (L + M) ganglion cells and with a decrease in the total L + M cone input to each S - (L + M) ganglion cell.

Brightness induction from uniform and complex surrounds: a general model.

We studied the brightness induced from complex non-figural achromatic surrounds. A spatially uniform test field was surrounded by a random texture composed of two sets of dots. The luminance of each set of dots was modulated sinusoidally at 0.5 Hz. The mean luminance, phase and amplitude of modulation of each set were controlled independently so as to modulate the luminance and/or the contrast of the surround. Brightness induction was measured by a modulation nulling technique. The results were fit by a model in which the total brightness induced by a surround is equal to a weighted spatial summation of the induced effects from each point in the surround. The model incorporates local luminance gain controls in the test and surround fields and assumes that the magnitude of induction from each surround element is gain controlled by the difference between the mean luminance of the test and the individual surround elements.