Biomedical subjects

B Pinna

Publications and source records attributed to B Pinna.

5 recordsLinked to original sources

PubMed1992

Amodal completion versus induced inhomogeneities in the organization of illusory figures.

An analysis is presented of a phenomenological model of illusory contours. The model is based on amodal completion as the primary factor giving rise to the illusory figure. In the experiment, conducted by the method of paired comparisons, the same parameter was manipulated in two series of equivalent configurations. The first series yielded examples of amodal completion, the second examples of illusory figures. Three groups of subjects evaluated the magnitude of completion, the brightness contrast of the illusory figure, and the contour clarity of the illusory figure. A control experiment was conducted, which demonstrated that in these configurations amodal completion and amodal continuation behave in the same way. Line displacement did not influence the brightness or the contour clarity of the illusory figures, though it influenced the magnitude of amodal completion. These results are in agreement with the energetic model developed by Sambin.

Adult↗

PubMed1991

Anomalous contours and illusion of angularity: phenomenal and theoretical comparisons.

Many experimental comparisons between real and anomalous contours have proven the functional equivalence of the two conditions; however, there are some contradictory findings. One of these is obtained by analyzing the anomalous contours in the light of a new illusion, called the 'illusion of angularity'. A circle becomes a polygon when it covers the centre of a radial arrangement of black stripes, and a polygon changes its perceptual shape depending on its orientation with respect to the same radial arrangement. Phenomenally, it appears like a very pointed polygon, in which every side is concave or, alternatively, a shape that looks like a circle with angles added in the spaces between the radial stripes, or a polygonal shape in which every side is convex. The reciprocal anomalous counterparts of these conditions, obtained by removing the geometrical/polygonal contours, reveal different results. In the first case, one sees a perfect circle; in the second case, a polygon with blunted vertices, or a circular shape with angular protrusions; in the third case, a deformed circle. These results are inconsistent with some theoretical models proposed to explain the emergence of anomalous contours, namely, all the top-down models expressed in terms of cognitive constructions and perceptual hypotheses, or in terms of global figural organizations. Rather, these comparisons suggest a different interpretation for the two phenomena (the illusion of angularity and anomalous contours). This interpretation is based on dynamic interactions or on network computations that synthesize both real and anomalous contours.

Adult↗

PubMed1991

A dynamic model for anomalous figures: the shape of line-induced brightness modifications.

It is recognized that a fundamental role in the perception of anomalous figures is played by the intensity and shape of brightness modifications induced by line ends. The aim of this work was to study the structure of these modifications experimentally, by using variously arranged dots as probes. It was thus assumed that dots can measure activations generated inside abrupt line ends. The results show distribution of activation which differs according to dot distance and angle with respect to the continuation of the line near its end. These data do not agree with the predictions of information processing models in the literature on anomalous figures, which are based on perceptually postulated figures accounting for unlikely gaps. However, they do agree with the dynamic model proposed here, which is based on the idea that certain figure characteristics, eg the differential brightness of anomalous figures, depend on activation distribution which in turn depends on the organization of the forces in play. This idea is rooted in Gestalt theory. Another model supported by our experimental data is Grossberg's neural dynamic approach. In this case too, the basic idea is that of activation distribution which depends on the interaction of complex neural networks functioning according to special algorithms.

Adult↗

PubMed1987

Observations on stroboscopic induced motion.

Subject-relative explanations of motion induction state that induced motion is the result of a misperceived shift of the median plane of the visual field of the subject. This theory does not require relative motion of the spot and frame, in the classical spot-and-frame condition, only asymmetrical stimulation. Three experiments are reported in which stroboscopic induced motion was investigated. The experimental arrangement was unconventional in that the induced object (spot) was presented only during the interstimulus interval between the exposures of the inducing object (frame). This allowed differentiation of the duration of the induced movement and that of the inducing one. In the first experiment it was demonstrated that perception of induced motion depends upon the duration of the interstimulus interval between the presentations of the inducing frame. In the second experiment it was shown that the perceived velocity of the induced movement can be different from that of the inducing one and depends on the duration of exposure of the induced object. In the third experiment a stimulus display was created in which the apparent displacement of an object and its induced motion are incongruous. The results are incompatible with subject-relative displacement as the sole determining factor of motion induction and they present some difficulties for the hypothesis that induced motion is the result of the apportionment of the objective displacement of the frame.

Adult↗

PubMedDate not supplied

Role of rHuEpo on blood transfusions in preterm infants after the fifteenth day of life.

The specific aim of the study was to assess the safety and efficacy of recombinant human erythropoietin (rHuEpo) in reducing the need for blood transfusions in preterm infants after the 15th day of life. Between 1 October 1994 and 1 October 1995, 107 preterm infants, gestational age < or = 34 weeks, were admitted to the Neonatal Intensive Care Unit and received rHuEpo subcutaneously, 900 U/kg week-1, 3 times weekly, supplemented with iron and vitamin E. Treatment was started at 8 days of life and lasted from a minimum of 6 weeks to a maximum of 3 months. A total of 116 preterm infants of the same gestational age, admitted to the Neonatal Intensive Care Unit from 1 January 1992 to 31 December 1992, served as controls. Entry criteria were gestational age < or = 34 weeks and no major congenital malformation. There were no differences in routine care between the two groups. Hematological measurements and transfusion requirements were followed during therapy. The infants were divided into two groups according to birth weight (< 1500 g and > or = 1500 g), and for each group the number of patients who received blood transfusions and when blood transfusions occurred, before or after the 15th day of life, was recorded. There was a statistically significant difference only for transfusions carried out after the 15th day of life (p < 0.002). No adverse effects attributable to rHuEpo during the treatment were noted. The results indicate that early rHuEpo treatment, in combination with iron supplements, is effective in reducing the need for blood transfusions in preterm infants after the 15th day of life.

Anemia, Neonatal↗