Intestinal morphology and enzymatic activity in newly weaned pigs fed contrasting fiber concentrations and fiber properties.

The main objective of this study was to determine the effect of fiber source and concentration on morphological characteristics, mucin staining pattern, and mucosal enzyme activities in the gastrointestinal tract of pigs. The experiment included 50 pigs from 10 litters weaned at 4 wk of age (BW 8.6 +/- 1.4 kg) and divided into 5 treatment groups. Diets containing fiber of various physico-chemical properties and concentrations were formulated to contain 73, 104, or 145 g of dietary fiber/kg of DM. The diets were based on raw wheat and barley flours. Pectin and barley hulls, representing soluble and insoluble fiber sources, respectively, were used to increase the fiber concentration. The pigs were fed the experimental diets for 9 d, and then the pigs were euthanized and the entire gastrointestinal tract was removed. Tissue samples were taken from the mid and distal small intestine and from the mid colon. Inclusion of pectin in the diets significantly decreased (P < 0.001) ADFI and ADG compared with pigs fed no pectin. The villi and the crypts were shorter in pigs fed pectin-containing diets, but the villous height/crypt depth ratio was unaltered. Pectin significantly decreased the area of mucins in the crypts of the small intestine, indicating that the pigs fed the pectin-containing diet would probably be more susceptible to pathogenic bacteria, although this cannot be separated from the impact on ADFI. The lectin-binding pattern of the intestinal mucosa was unaffected by diet. The activity of lactase and maltase was increased in pigs fed diets with high fiber content, whereas sucrase activity was increased in pigs fed the pectin-containing diets. The activity of the peptidases, aminopeptidase N and dipeptidylpeptidase IV, was increased when feeding high fiber diets, whereas the activity of gamma-glutamyl transpeptidase remained unaffected by the experimental diets. In conclusion, the reduced feed intake observed with the pectin-containing diets could explain the lower villous height and crypt depth observed in this study. However, direct effects of pectin also are possible, and thus further study is warranted. Feeding pigs high insoluble fiber diets improved gut morphology by increasing villi length and increased mucosal enzyme activity when compared with pigs fed pectin-containing diets. The mucin content as determined by staining characteristics suggests that pigs fed high insoluble fiber diets might be better protected against pathogenic bacteria than pigs fed diets high in soluble fiber.

Multiple gain control processes in contrast-contrast phenomena.

Spatial interactions among orientation-tuned gain control processes are presumed to mediate center-surround contrast-contrast phenomena. In this paper, we assess contributions of gain control processes that pool over orientation. We measured the apparent contrast of a luminance-modulated center disk embedded in various modulated surrounds. In all conditions, observers compared the apparent contrast of the test center to an identically modulated disk with no surround. When center and surround are simple, vertical sinusoids and presented in phase, suppression depends upon surround contrast and is marked at high contrasts. When components are presented 180 degrees out of phase, no suppression occurs at any contrast. When a horizontal component is added to the surround, much less suppression occurs. However, strong suppression is reinstated when both center and surround are plaids. Neither of the latter two effects are phase dependent. We suggest that two different sources of gain control are revealed by the simple sinusoidal and the plaid stimuli. One is orientation tuned and phase-dependent. The other pools over all orientations and includes neurons tuned to multiple phases.

Ad libitum mixing in a taste memory task: methodological issues.

Ad libitum mixing, an application of the method of adjustment in food research, was investigated and evaluated for the purpose of taste memory research. The difference between ascending and descending runs in mixing was studied using a wide range of prefill concentrations lower and higher than standard. The effect of training was studied by comparing subjects with two or 10 replications in the first session where a standard was present as a reference. Results showing higher reproduced concentrations after a 25 h time interval than those produced immediately are consistent with earlier results from within-subject designs. Thus, the difference in recall performance did not depend on the design of the study. No difference between ascending and descending runs in the mixing was observed, thus the prefill concentrations did not affect the reproduction of a given standard. There was no significant difference between produced concentrations after two and 10 replications, although a non-significant trend towards improved performance following 10 replications was observed after the 25 h time interval.

Recalling sweet taste intensities in the presence and absence of other tastes.

Memory for sweet taste intensities in different media during 125 h was investigated using three concentrations (w/w) of sucrose: 4.21% (0.125 M), 8.28% (0.25 M) and 16.06% (0.5 M). Sucrose was dissolved in four media [water with no tastant and water with 0.73% (0.125 M) sodium chloride, 0.04% (0.002 M) citric acid and 0.04% (0.002 M) caffeine] as standard stimuli. Subjects (n = 39) were assigned into four groups, each group performing the memory task in one medium only. After tasting each standard the subjects reproduced the subjective taste intensity immediately and after 12 min and 1, 5, 25 and 125 h by mixing portions of low (0%) and high (29.75%; 1 M) concentrations (w/w) of sucrose and by tasting and retasting (ad libitum procedure). The produced sucrose concentrations increased significantly from the first session to the 125 h time interval. There was a significant difference between immediately reproduced standard concentrations and concentrations produced after all time intervals. Relative differences from standard (delta i/i) differed only between concentrations produced immediately and after 125 h time interval. The low (4.21%) concentration showed larger differences from standard than the high (16.06%) concentration. The added tastant had no effect on the results.

Illusory perception of gratings stimulating a small number of neurones.

We studied pattern perceptions caused by drifting gratings presented monocularly in the nasal and temporal visual fields at various suprathreshold contrasts. The grating and its surround and background were matched in luminance. Small grating produced illusions and reduced perceptions. When grating area or contrast increased from a subthreshold value, the gratings were first seen as mere flashes. Then each grating was sometimes perceived as a single small bright spot or point. Next each grating was seen as a single dark or bright line. Finally the stimuli were perceived as gratings consisting of several bars. Orientation or direction of movement were perceived correctly, but velocity, colour and number of bars were often perceived as illusions. Thus, in spite of the illusions, some features of the stimuli could have allowed correct discriminations. The area and contrast limits of illusory perception depended on eccentricity. Irrespective of retinal size, the stimuli were not perceived correctly as gratings at any eccentricities when the gratings were smaller than about 1 x 1 mm in their calculated cortical area and stimulated a small constant number of retinal ganglion cells. Relations between the results and retinal aliasing, cortical columns and phase locking of neuronal oscillations are discussed.

Mismatch negativity (MMN) for sequences of auditory and visual stimuli: evidence for a mechanism specific to the auditory modality.

ERPs to sequences of standard and deviant sinusoidal 100 msec tone pips, high-contrast sinusoidal gratings and to their simultaneously presented combinations were recorded. Mismatch negativity (MMN), an ERP component elicited by deviant stimuli, was estimated for the different stimulus sequences in order to find out whether it reflects modality-specific processes or non-specific attentive phenomena. In addition to the auditory modality, we studied whether the mismatch response could be evoked by a deviant visual stimulus in a visual sequence or by a deviant stimulus in either modality. The results show that only auditory stimuli produced the mismatch response, suggesting that MMN is not a manifestation of a general attentional mechanism but is probably specific to the auditory modality.

Sampling irregularity perturbs visual reconstruction.

We explored the human observer's ability to detect and discriminate sine-wave and square-wave gratings that were sampled at intervals varying from 4.7 to 9.4 arcmin. To study the effect of sampling irregularity on visual performance, we varied the position of each line sample on the basis of a Gaussian probability distribution, the standard deviation of which varied from 0 (regular sampling) to 4.7 arcmin (highly irregular sampling). The results indicate that irregular sampling has no systematic effect on the observer's ability merely to detect the presence of a sine- or square-wave grating. In contrast, sampling irregularity strongly impairs the subject's ability to discriminate between these waveforms. A model based on the convolution of difference-of-Gaussians-type weighting profiles predicted that sampling irregularity should have little to no effect on the output of a channel tuned to the third harmonic of the square-wave grating. The findings thus suggest the existence of a sampling scheme in the visual system. This scheme is based on local feature-selective mechanisms, probably edge detectors, that are highly sensitive to the relative position of the sample points in the space domain.

Apparent contrast of spatially and temporally sampled gratings.

We have measured the apparent contrast of spatially and temporally sampled gratings having the spatial frequency of 2, 4 and 8 c/deg. A contrast matching task was used in two different sampling conditions which allowed us to stimulate selectively the sustained and transient mechanisms in spatial and temporal vision. The results demonstrate the visual interpolation characteristics in the two domains and suggest a better response linearity for spatial than for temporal interpolation. The strongest nonlinear responses were obtained for temporally sampled medium spatial frequency gratings, suggesting separate temporal processing mechanisms for medium and high spatial frequencies

Fatal epithelioid haemangioendothelioma presenting in the lung and liver.

Three patients with epithelioid haemangioendothelioma (EHE) are described. Two patients presented with pulmonary infiltrates and one with a hepatic tumour. All had a metastatic disease ending fatally, and all were autopsied. The diagnosis was confirmed either by immunohistological or ultrastructural analysis. All three tumours were cytokeratin-negative and vimentin-positive, while only two contained cells reacting with the antibody of factor VIII-related antigen. Electron microscopy of the third tumour revealed features indicating endothelial differentiation. A short literature review is also presented demonstrating that the outlook of EHE is worse than previously thought.

Visual illusion mimicking dyslexia. A case history.

A 14-year-old girl with reading difficulties was found to have an unusual illusory movement of objects in the central visual field. The movement could be blocked by using a 26 mm Visolette magnifier with an arrow pasted on its lower surface to function as a reference point. After having read with help of this arrangement for 19 months the girl suddenly could see normally and has now been able to read without difficulties for over 3 years. We report the first documented case of visual illusion as the cause of reading difficulty which disappeared at the age of 15 years, thus years after the maturation of visual functions is thought to be completed. Although visual illusion like the one presented here must be rare, it should be diagnosed, because the treatment is totally different from that of usual dyslexia.

Temporal integration and contrast sensitivity in foveal and peripheral vision.

Spatial contrast sensitivity functions and temporal integration functions for gratings with dark surrounds were measured at various eccentricities in photopic vision. Contrast sensitivity decreased with increasing eccentricity at all exposure durations and spatial frequencies tested. The decrease was faster at high than at low spatial frequencies, but similar at different exposure durations. When cortically similar stimulus conditions were produced at different eccentricities by M-scaling, contrast sensitivity became independent of visual field location at all exposure durations tested. The results support the view that in photopic vision spatiotemporal information processing is qualitatively similar across the visual field, and that quantitative differences result from retino-topical differences in ganglion cell sampling. For gratings of constant retinal area temporal integration (improvement of contrast sensitivity with increasing exposure duration) was more extensive at high than at low retinal spatial frequencies but independent of cortical spatial frequency and eccentricity. For M-scaled gratings temporal integration was more extensive at high than at low cortical spatial frequencies but independent of retinal spatial frequency and eccentricity. The results suggest that the primary determinant of temporal integration is not spatial frequency but grating value that is calculated as AF2 square cycles (cycle2), where A is grating area and F spatial frequency.

Contrast sensitivity in monocular glaucoma.

The results of this selected group of glaucoma patients demonstrate that the effect of glaucoma on the contrast sensitivity can be assessed only after careful exclusion of all other causes for decrease in contrast sensitivity. Further development of methods is necessary.

Contrast sensitivity in evaluation of visual impairment due to macular degeneration and optic nerve lesions.

Spatial contrast sensitivity was investigated in a group of 17 patients with macular degeneration or optic atrophy. It has been reported earlier that patients with optic atrophy may have reduced contrast sensitivity at low spatial frequencies without decrease of visual acuity, a phenomenon called 'hidden visual loss'. The present study shows that also the opposite may be true: patients with macular degeneration or optic atrophy may have greatly decreased visual acuity and yet normal or nearly normal contrast sensitivity at low spatial frequencies and reasonably good sensitivity at intermediate spatial frequencies. This phenomenon could be called 'hidden vision'. In normal individuals and many visually impaired patients the spatial contrast sensitivity at high and intermediate spatial frequencies is equal when measured using grating fields of different size. In patients with central scotoma due to macular degeneration or optic atrophy contrast sensitivity is dependent on the size of the grating field: the maximal contrast sensitivity is higher when larger grating fields are used. The size of the smallest grating field that is needed for normal contrast sensitivity values at low spatial frequencies is one measure of visual impairment in this group of patients. Another measure of the function of the eccentric viewing area is the grating acuity which may also vary as a function of the grating field size.

Contrast sensitivity in evaluation of visual impairment due to diabetes.

Spatial contrast sensitivity of 19 diabetics with different degrees of visual impairment was studied. It was found that contrast sensitivity at intermediate and low spatial frequencies may decrease without corresponding loss of visual acuity. In advanced cases of diabetes the opposite may be true: contrast sensitivity was better than expected on the basis of visual acuity. Thus both visual acuity and contrast sensitivity measurements are useful in the evaluation of the nature of visual impairment due to diabetic eye disease.