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Biomedical subjects

Z J He

Publications and source records attributed to Z J He.

31 records · Page 2Linked to original sources
PubMed1994

Apparent motion determined by surface layout not by disparity or three-dimensional distance.

The most meaningful events ecologically, including the motion of objects, occur in relation to or on surfaces. We run along the ground, cars travel on roads, balls roll across lawns, and so on. Even though there are other motions, such as flying of birds, it is likely that motion along surfaces is more frequent and more significant biologically. To examine whether events occurring in relation to surfaces have a preferred status in terms of visual representation, we asked whether the phenomenon of apparent motion would show a preference for motion attached to surfaces. We used a competitive three-dimensional motion paradigm and found that there is a preference to see motion between tokens placed within the same disparity as opposed to different planes. Supporting our surface-layout hypothesis, the effect of disparity was eliminated either by slanting the tokens so that they were all seen within the same surface plane or by inserting a single slanted background surface upon which the tokens could rest. Additionally, a highly curved stereoscopic surface led to the perception of a more circuitous motion path defined by that surface, instead of the shortest path in three-dimensional space.

Depth Perception↗
PubMed1994

Perceived surface shape not features determines correspondence strength in apparent motion.

Previous psychophysical studies have revealed that shape similarity can affect apparent motion correspondence. Such results however, do not specify the level of representation, at which shape similarity is defined. We sought to understand this question by using a 2 x 2 competitive apparent motion paradigm. We manipulated the binocular disparity of the motion stimuli (tokens) relative to adjacent squares to selectively change the internal surface representation of the tokens while keeping early filtered representation intact. When two sets of differently oriented tokens (45 degrees,-45 degrees bars) were used, there was a preference for seeing motion between tokens having the same orientation. However, such a motion bias was reduced when tokens became part of a large surface square seen either as amodally occluded in the background or as a transparent surface modally completed in front. Since shape differences at the early filtering level remain essentially intact (i.e. + 45 degrees vs -45 degrees) our findings support the surface level hypothesis. Perceived surface shape rather than shape defined by early filters largely determines motion correspondence.

Form Perception↗
PubMed1994

Perceiving textures: beyond filtering.

Classical texture segregation theory and current visual filtering models suggest that rapid texture segregation is determined by the properties of early cortical filtering. To examine this assumption, we manipulated the binocular disparity of texture elements (an L vs a bar) relative to adjoining squares. Such a manipulation has little effect on the early cortical filtered representations of the stimuli but can have a strong influence on surface representation. In particular, it can determine whether an image patch is seen as a distinct surface, in front, or part of a larger occluded surface, in back. When seen as part of an occluded surface, the distinctive shape of each texture element is reduced. Accordingly, we found that texture discrimination performance was impaired when the texture elements had uncrossed disparities ("back" case). Additional experiments indicated that this result was not due to the disparity manipulation alone, but occurred only when each texture element was perceived as part of an occluded surface. We conclude that in rapid texture discrimination, the visual system cannot ignore information regarding surface layout. This suggests that for purposes of texture perception, either: (a) the visual system has no access to the filtered image or (b) one cannot entertain the concept of a filtered image uninfluenced by higher order surface processing.

Depth Perception↗
PubMed1992

Surfaces versus features in visual search.

Often implicit in the interpretation of visual search tasks is the assumption that the detection of targets is determined by the feature-coding properties of low-level visual processing. But higher level processes have also been implicated as visual search ability is enhanced in a depth plane or when two-dimensional shapes are interpreted as three-dimensional forms. Here we manipulate binocular disparity to degrade visual search, so that otherwise identical features become parts of surfaces through perceptual completion, rendering them less clearly distinguishable as targets and distractors. Our results indicate that visual search has little or no access to the processing level of feature extraction but must have as an input a higher level process of surface representation.

Humans↗
PubMed1992

Spectral sensitivity of monocularly deprived cats.

The reports of rod-dominated psychophysical spectral sensitivity from the deprived eye of monocularly lid-sutured (MD) monkeys are intriguing but difficult to reconcile with the absence of any reported deprivation effects in retina. As most studies of MD retina have been from cat, we have examined psychophysically the increment threshold spectral sensitivity of MD cats using both reaction time and simultaneous two-choice behavioral procedures. Although the deprived eyes exhibited an absolute increment threshold sensitivity deficit, both rod and cone spectral sensitivity functions were obtained on large white backgrounds. This normal transition from rod to cone vision, as background luminance increased, was also found in threshold vs. intensity functions. Using their deprived eye, some cats exhibited a rod spectral sensitivity function when a smaller, normally photopic, background was used providing some support for a hypothesis that the rod-dominated spectral sensitivity observed in monkey may represent detection of scattered stimulus light. Alternatively monocular deprivation may reveal a rod-dominated mechanism which exists in monkey but not in cat.

Animals↗
PubMed1991

Luminance sensitivity recovers quickly in monocularly deprived cats.

We measured increment thresholds, using a reaction time or two-choice behavioral technique, in three cats monocularly deprived of normal vision for 14-16 months. Luminance increment thresholds could be obtained as early as nine days after lid opening and improved by 0.5-2.0 log units over the next few weeks. Also, visual reaction times decreased during the sensitivity improvement. When compared to the data for grating discrimination, these results suggest that visual recovery from monocular deprivation may proceed at different rates for different psychophysical discriminations.

Animals↗
PubMed1991

[The qualitative and quantitative diagnostic significance of P-VEP in the evaluation of glaucomatous visual function damage].

The pattern visual evoked potential (P-VEP) and the central visual field in 63 cases (95 eyes) of primary glaucoma were simultaneously measured with the American Compact Four electrophysiology apparatus and the Chinese TBC-IA central field analyzer. The data showed that the mean latency of P1 in the glaucomatous eyes was significantly lengthened, and this occurred before the visual field and disk abnormalities, indicating that VEP is sensitive in the detection of early glaucoma. Furthermore, the VEP changes were consistent with the central visual field defects qualitatively and quantitatively. Therefore, the latency of P1 can be a useful quantitative index in the evaluation of glaucomatous visual function damage. The difference in diagnostic sensitivity to glaucoma between VEP and visual field changes were discussed. The authors suggest that combination of the two may be a more useful index.

Adult↗
PubMed1990

Peripheral field stimulation affects foveal flicker, but not color, sensitivity.

Human observers have different thresholds for flicker detection and color detection of a rapidly flickering spectral stimulus presented on a steady white background. A flickering surround, which did not overlap the stimulus or background, reduced flicker sensitivity but not color sensitivity for both monocular and binocular viewing. However, a flickering surround presented to one eye had no influence upon either color or flicker thresholds of the other eye.

Adult↗
PubMed1987

Effects of patterned backgrounds on responses of lateral geniculate neurons in cat.

In the lateral geniculate nucleus (LGN) of paralyzed cats under urethane anaesthesia, an extensive disinhibitory region (DIR) outside the inhibitory surround of the receptive field (RF) was found in both sustained and transient cells. Its extent is comparable to that of McIlwain's periphery effect (1964). The responses to a light spot, flashed into different parts of the RF center, were used to assess the effect of different background patterns, located over the DIR, on responsiveness and receptive field organization. A straight line background cutting across the RF center led to a marked shrinkage in RF size and to a suppression of the center response. In sustained cells, these influences were not due to the light flux of the background, but were mainly due to the spatial property of the line itself. This was demonstrated by comparing the effect of a straight line background with that of a zigzag line or of distributed dots. The light flux for the different patterns and their spatial weighting was the same, so that they differed from each other solely in their form. A straight line background elicited much stronger suppression of the center response and more marked shrinkage of the RF than if the component dots are dispersed over a wider area, but keeping the radial distances of the individual dots from the RF-center constant. The data suggest that the dispersion of the component dots in different backgrounds plays an important role as response amplitude and RF diameter increase proportional to the dispersive area of the background patterns. For transient cells, all backgrounds used showed similar effects on center responses and RF diameter, indicating that for them it was the light flux of the backgrounds rather than their spatial property that caused the effects.

Action Potentials↗
PubMedDate not supplied

Effects on endogenous acetaldehyde production by disulfiram and ethanol feeding on rat pancreas.

Exogenous acetaldehyde infusion can induce pancreatitis-like injury of the pancreas in some isolated pancreas models, whereas in vivo such treatment has failed to induce pancreatitis. In vivo exogenous acetaldehyde may not be effective because it is rapidly metabolized. The aim of this study was to investigate whether endogenous acetaldehyde accumulates in the pancreas after ethanol feeding when acetaldehyde metabolism is blocked by disulfiram, and whether this treatment can induce pancreatitis-like injury in the rat. The liver was studied for comparison. In part I of the experiment, adult male Wistar rats were given water (n = 24), ethanol (n = 24), disulfiram (n = 24), and ethanol plus disulfiram for 1 week (n = 24) or 3 weeks (n = 24) and for 3 weeks with (n = 6) and without (n = 6) hypovolemia. In part II of the experiment, rats were given water (n = 6), ethanol (n = 6), and high-dose disulfiram (n = 6) and ethanol plus high-dose disulfiram (n = 6). Ethanol and acetaldehyde concentrations in blood, liver, and pancreas were measured. Animal behavior was monitored, and weight changes, plasma amylase activity, water content, and histomorphology of the pancreas and liver were studied without knowing the group. No increases in plasma amylase activity and no histomorphologic changes in the pancreas were observed under light or electron microscopy in part I of the experiment. In part II, treatment with ethanol induced acetaldehyde accumulation in the liver (33.6 +/- 2.6 micromol/L), but to a lesser degree in the blood (9.6 +/- micromol/L) and pancreas (5.0 +/-.2 micromol/L). Ethanol plus disulfiram induced marked accumulation of acetaldehyde in the liver (83.2 +/- 15.9 micromol/L), blood (280.0 +/- 47.4 micromol/L), and pancreas (43.6 +/- 4.7 micromol/L). When tissue acetaldehyde levels reached 30 to 40 micromol/L, we found a decrease in zymogen granules along with formation of small intracytoplasmic vacuolizations in the acinar cells and accumulation of lipid droplets in the hepatocytes, whereas physiologic signs of pancreatitis (hyperamylasemia, edema) or increases in liver enzymes did not develop. High levels of acetaldehyde accumulate in the liver and pancreas with the treatment described. Although this was accompanied by lipid degeneration of the hepatocytes and some subcellular changes in the acinar cells, physiologic signs of pancreatitis did not develop. Thus acetaldehyde accumulation alone, or in combination with hypovolemia, is not responsible for the induction of acute pancreatitis.

Acetaldehyde↗