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Biomedical subjects

L Tommasi

Publications and source records attributed to L Tommasi.

14 recordsLinked to original sources
PubMed2003

Phenolic compounds and antioxidant activity from red grape marc extracts.

The aims of this work were to determine the amounts of the different classes of phenolic compounds in an ethanolic extract from red grape marc and its components, peels and seeds, and to evaluate their antioxidant activities by the beta-carotene bleaching test for their utilization as natural antioxidants. The results showed that red grape marc was rich in polyphenol compounds with a clear antioxidant activity. The extracts, in fact, at very low concentration (20 ppm) in total phenols showed an antioxidant activity (AA) higher than 43% on average, while at higher concentration (80-160 ppm) all the fractions had an AA comparable to that of butlylated-hydroxytoluene. Grape seeds seemed to give the highest contribution to such AA, as they contained high quantities of proanthocyanidines, a type of flavonoid known for its high antioxidant properties.

Antioxidants↗
PubMed2001

How birds use their eyes: Opposite left-right specialization for the lateral and frontal visual hemifield in the domestic chick.

Recent evidence has demonstrated that, in animals with laterally placed eyes, functional cerebral asymmetry is revealed by preferential use of either the left or right eye in a range of behaviors (birds: [1, 2, 3]; fish: [4, 5]; reptiles: [6, 7]). These findings pose a theoretical problem. It seems that there would be disadvantages in having a substantial degree of asymmetry in the use of the two eyes; a deficit on one side would leave the organism vulnerable to attack on that side or unable to exploit resources appearing on one side. We here report a possible solution to the problem. We have found that domestic chicks show selective use of the lateral visual field of the left eye and of the right hemifield in the binocular, frontal visual field when they peck at strangers but not at cagemates. Thus, during social recognition, there seems to be opposite and complementary left-right specialization for the lateral and frontal visual fields of the two eyes. These findings can reconcile the computational advantages associated with asymmetry of the left and right sides of the brain with the ecological demands for an animal to perceive and respond equally well to the left and right sides of its midline.

Animals↗
PubMed2001

Illusory smoke and dazzling fog.

It is well known that a flat ellipse rotating in the frontoparallel plane appears, after brief inspection, as a rigid circular disc tilting back and forth in a 3-D space. We here report that rotation of a grey-shaded ellipse on a white or on a black background produces the compelling illusion of a dark smoke or a dazzling fog (depending on the conditions of the background) moving in front of a completely white or completely black tilting disc. The fog effect disappears when there is a luminance contrast all along the perimeter of the ellipse. An experiment is reported showing that the effect can be experienced in static conditions only to a limited extent and mostly in the 'dazzling' version, and that relative movement between the contours of the figure and the shaded area is crucial to the occurrence of the effect, while the occurrence of a depth effect is not.

Humans↗
PubMed2001

Encoding of geometric and landmark information in the left and right hemispheres of the Avian Brain.

Chicks were trained binocularly to find food buried under sawdust in the center of a square enclosure. When tested in an enclosure made larger or smaller in size, binocular and left-eyed chicks searched mainly on the basis of relative distance of the food from the enclosure walls, whereas right-eyed chicks searched on the basis of absolute distance. Moreover, binocular and left-eyed chicks relied mainly on global spatial information (i.e., distances from the walls), whereas right-eyed chicks also used information provided by visual landmarks. These results suggest that the right hemisphere of the avian brain (fed mostly by the left eye) is primarily concerned with encoding of relational spatial information, whereas the left hemisphere (fed mainly by the right eye) is concerned with absolute metric information, possibly as part of an encoding strategy based primarily on local (both spatial and nonspatial) cues.

Animals↗
PubMed2000

Motor control by vision and the evolution of cerebral lateralization.

Chicks (4 or 5 days old), which are able to use either eye freely, use the right eye (RE) preferentially in approach to a food dish when a lid, which has to be removed, is visible during approach. They use the left eye (LE) instead when no manipulation is required, but the same dish is similarly visible. The RE is also used preferentially in selecting food grains scattered over the floor; RE use in these two contexts is thus associated with visual control which brings the bill in planned contact with a visible target rather than with approach to a site where it is anticipated that feeding will occur. Zebrafish also use the RE preferentially when preparing to bite a target; during purely visual examination of the same target, this preference disappears. This evidence is used together with evolutionary evidence to support a new hypothesis for the origin of cerebral lateralization: paired anterior eyes evolved in filter-feeding ancestors of the vertebrates as part of the acquisition of prey catching. A key use for early vision was to predict likely contact with prey so as to inhibit reflexes of rejection and avoidance normally elicitated by tactile input to the mouth and so to allow ingestion. Innervation of mouth structures by the left side of the CNS caused control of mouth reflexes to become predominantly a left CNS affair. As visual abilities developed this starting condition meant that control of manipulation (which is by the mouth for most vertebrates) remained predominantly with the left side of the CNS.

Animals↗
PubMed2000

Eye use in search is determined by the nature of task in the domestic chick (Gallus gallus).

In Experiments 1-3 chicks were trained to find, using both eyes, food covered by a cap, using wide-angle search so as to involve lateral and frontal visual fields, with either local or positional cues, or both, identifying the baited site. At test they used right, left or both eyes (RE, LE, Bin). When both types of cue were relevant, LE made greater use of positional cues than the other two groups, as has been previously found, whereas RE made greater use of local (colour) cues. However, when only one type of cue was relevant, RE and LE were equally able to use positional or local cues. Right/left differences emerge when RE and LE can be used in different ways during training. In Experiments 4-5 Bin chicks were shown to turn preferentially to the right during wide-angle search, when relying on local, and to the left when relying on positional cues. In search, parallel processing of RE and LE inputs appears to allow competition which is usually won by the eye system more suited to the task, which then initiates targeting to objects which are visible to its eye.

Analysis of Variance↗
PubMed2000

Searching for the center: spatial cognition in the domestic chick (Gallus gallus).

Chicks learned to find food hidden under sawdust by ground-scratching in the central position of the floor of a closed arena. When tested inan arena of identical shape but a larger area, chicks searched at 2 different locations, one corresponding to the correct distance (i.e., center) in the smaller (training) arena and the other to the actual center of the test arena. When tested in an arena of the same shape but a smaller area, chicks searched in the center of it. These results suggest that chicks are able to encode information on the absolute and relative distance of the food from the walls of the arena. After training in the presence of a landmark located at the center of the arena, animals searched at the center even after the removal of the landmark. Marked changes in the height of the walls of the arena produced some displacement in searching behavior, suggesting that chicks used the angular size of the walls to estimate distances.

Animals↗
PubMed1999

Figure ground segregation modulates perceived direction of ambiguous moving gratings and plaids.

A translating oriented grating viewed through a circular aperture with an occluding area in the middle appeared to move alternately in an oblique or in a vertical direction depending on the foreground/background assignment on the central occluding area. The effect occurred even when the central area was simply removed from the display, thus giving rise to a 'subjective' occluder. Parametric studies revealed that the probability of seeing oblique or vertical motion was affected by the size of the central area but not by its contrast relationships with the grating. Similar phenomena of ambiguous motion direction were observed using changes in colour along a translating grating that produced neon colour spreading effects, or using oriented edge discontinuities that collapsed into subjective plaids composed of two one-dimensional gratings. These results are discussed with respect to the hypothesis that surface segmentation mechanisms play a crucial part in the interpretation of motion signals.

Color Perception↗
PubMed1998

Systemic manifestations and liver disease in patients with chronic hepatitis C and type II or III mixed cryoglobulinaemia.

The aim of this study was to evaluate the prevalence of cryoglobulins in patients with chronic hepatitis B and C virus infection and to investigate the association of type II and type III mixed cryoglobulinaemia with systemic manifestations and liver disease stage and outcome in hepatitis C virus (HCV)-positive patients. We analysed the prevalence of cryoglobulinaemia in a cohort of patients with chronic liver disease and compared the systemic manifestations and liver involvement in HCV-positive patients with type II or type III mixed cryoglobulinaemia. The prevalence of serum cryoglobulins was significantly higher in HCV-positive patients than in hepatitis B surface antigen (HBsAg)-positive patients (55.4 vs 20.6%). In HCV-positive patients, stage of liver disease correlated with the prevalence of cryoglobulinaemia. Patients with type II cryoglobulins showed a significantly higher risk of cirrhosis and of extrahepatic manifestations while patients with type III cryoglobulins had a significantly higher prevalence of hepatocellular carcinoma. During follow-up the former had an odds ratio of 11.9 of death from extrahepatic complications while the latter had an odds ratio of 3.4 of dying from hepatic disease. Our study confirms the high frequency of mixed cryoglobulinaemia in patients with chronic hepatitis C virus infection. The presence and type of cryoglobulins seem to be associated with different clinical manifestations and outcome.

Adolescent↗
PubMed1997

Young chickens learn to localize the centre of a spatial environment.

Young chickens were trained to find food by ground-scratching in the centre of a closed uniform arena and were then tested in arenas of similar areas but of different shapes. Chickens showed localized searching behaviour in the square-shaped arena, and maintained this behaviour when placed in a circular or triangular (both equilateral and isosceles) arena. With a rectangular-shaped arena, obtained by doubling the original square-shaped one, chickens showed more dispersed searching along the major axis, but searching tended to be concentrated around the centres of the composing squares and around the centre of the rectangle itself. When trained in a square- or triangle-shaped arena and then tested in an arena of the same shape but a larger area, chickens displayed searching behaviour at two different distances from the wall of the arena, one corresponding to the correct distance (i.e. centre) in the smaller (training) arena, the other to the actual centre of the test arena. On the other hand, in a circular arena, chickens searched mainly at a distance midway between the radius of the small (training) and of the large (testing) circular arena. These results suggest that, during training, chickens encoded information on both the absolute and the relative distance of the food from the walls of the arena, the latter information being more accurate when the arena displayed identifiable features such as corners.

Animals↗
PubMed1996

Lateral asymmetries due to preferences in eye use during visual discrimination learning in chicks.

Chicks were trained to discriminate between two boxes of the same colour (white) on the basis of their positions using the pecking response. Some chicks were trained to peck at the box on their right side, some at the box on their left side. They were then retrained with two boxes of different colours (one red the other green): in one group of chicks the position of the two boxes was randomly alternated in the various trials (thus making colour a conspicuous but irrelevant cue), in the other it was maintained unchanged. A control group was retrained with two white boxes identical to those used during training. In all of the three groups chicks had to discriminate between the two boxes on the basis of their positions. During training, chicks took less trial and errors to learn when the positive box was placed on their right side and the same occurred during retraining with boxes that maintained a fixed position and during retraining in the control condition. During retraining with position alternation, on the contrary, chicks took less trials and errors to learn when the positive box was placed on their left side. Video recording of the chicks' behaviour while approaching the boxes showed that these lateral asymmetries reflect head and body turning associated to preferences in eye use, likely due to the different specializations of contralateral brain structures. It is argued that position cues engage the right hemisphere, with consequent head turning to the right to allow lateral viewing by the left eye; object-specific cues engage the left hemisphere, with consequent head turning to the left to allow lateral viewing by the right eye.

Animals↗
PubMed1995

Solving occlusion indeterminacy in chromatically homogeneous patterns.

Overlapping figures can produce consistent depth stratification even when chromatically homogeneous. Since neither T-junctions nor X-junctions are present in these patterns, the problem arises of what rules determine the direction of depth stratification, ie which surfaces appear in front and which behind. In a series of demonstrations and formal experiments involving perception of stereopsis, motion, transparency, motion in depth, and reversible figures, the validity of the principle that the visual system tends to minimise the formation of interpolated modal contours was tested. The reason why larger surfaces tend to be seen modally in front, rather than behind, would reflect the geometrical property that when, in overlapping objects, larger surfaces are closer there will be shorter occluding boundaries than when smaller surfaces are closer. It is shown that this constraint is independent of the empirical depth cue of relative size. An example is also given of a simple computational strategy that extracts, from chromatically homogeneous patterns, occluding subjective contours corresponding to those perceived by human observers.

Attention↗
PubMed1986

[Recurrent purulent meningitis and deafness: Mondini's malformation].

A 5-year-old girl with severe deafness (90 dB) had two successive attacks of bacterial meningitis. A vesicular cochlea was found on polytomography, and a bilateral defect in the stapes footplate with cerebrospinal fluid leakage during surgery (Mondini dysplasia). Although rare, the eventuality of this malformation emphasises the utility of polytomography of the inner ear in children with congenital deafness.

Bacterial Infections↗