PubMed Health⌕ Search

Biomedical subjects

F Bonato

Publications and source records attributed to F Bonato.

7 recordsLinked to original sources
PubMed2000

The effects of figure/ground, perceived area, and target saliency on the luminosity threshold.

Observers adjusted the luminance of a target region until it began to appear self-luminous, or glowing. In Experiment 1, the target was either a face-shaped region (figure) or a non-face-shaped region (ground) of identical area that appeared to be the face's background. In Experiment 2, the target was a square or a trapezoid of identical area that appeared as a tilted rectangle. In Experiment 3, the target was a square surrounded by square, circular, or diamond-shaped elements. Targets that (1) were perceived as figures, (2) were phenomenally small in area, or (3) did not group well with other elements in the array because of shape appeared self-luminous at significantly lower luminance levels. These results indicate that like lightness perception, the luminosity threshold is influenced by perceptual organization and is not based on low-level retinal processes alone.

Adult↗
PubMed1999

An anchoring theory of lightness perception.

A review of the field of lightness perception from Helmholtz to the present shows the most adequate theories of lightness perception to be the intrinsic image models. Nevertheless, these models fail on 2 important counts: They contain no anchoring rule, and they fail to account for the pattern of errors in surface lightness. Recent work on both the anchoring problem and the problem of errors has produced a new model of lightness perception, one that is qualitatively different from the intrinsic image models. The new model, which is based on a combination of local and global anchoring of lightness values, appears to provide an unprecedented account of a wide range of empirical results, both classical and recent, especially the pattern of errors. It provides a unified account of both illumination-dependent failures of constancy and background-dependent failures of constancy, resolving a number of long-standing puzzles.

Gestalt Theory↗
PubMed1999

Perceived area and the luminosity threshold.

Observers made forced-choice opaque/luminous responses to targets of varying luminance and varying size presented (1) on the wall of a laboratory, (2) as a disk within an annulus, and (3) embedded within a Mondrian array presented within a vision tunnel. Lightness matches were also made for nearby opaque surfaces. The results show that the threshold luminance value at which a target begins to appear self-luminous increases with its size, defined as perceived size, not retinal size. More generally, the larger the target, the more an increase in its luminance induces grayness/blackness into the surround and the less it induces luminosity into the target, and vice versa. Corresponding to this luminosity/grayness tradeoff, there appears to be an invariant: Across a wide variety of conditions, a target begins to appear luminous when its luminance is about 1.7 times that of a surface that would appear white in the same illumination. These results show that the luminosity threshold behaves like a surface lightness value--the maximum lightness value, in fact--and is subject to the same laws of anchoring (such as the area rule proposed by Li & Gilchrist, 1999) as surface lightness.

Humans↗
PubMed1994

The perception of luminosity on different backgrounds and in different illuminations.

Observers were presented with target surfaces of varying luminance and asked to report whether they appeared luminous or opaque. In one experiment the targets were presented against three backgrounds, white, gray, and black. In another experiment the targets were presented within Mondrian patterns that were either brightly or dimly illuminated. The results indicate that, across a variety of conditions, a target begins to appear luminous when its luminance is about 1.7 times that of a surface that would appear white in the same illumination, whether or not a white surface is available in the visual field for comparison. Defined in this way the luminosity threshold exhibits the two main kinds of constancy characteristic of surface grays, constancy with respect to changes in the illumination level and constancy with respect to changes in the reflectance of the immediate background. This finding, while challenging a range of potential rules, places the problem of defining the conditions that produce luminosity squarely within the problem of lightness perception for opaque surfaces.

Color Perception↗
PubMed1987

Recurrent life-threatening epistaxis in a child with Bernard-Soulier syndrome controlled by bilateral ligation of external carotids and ethmoidal arteries.

Bilateral ligation of external carotids and ethmoidal arteries proved successful in controlling severe recurring epistaxis in a 13-year-old patient with Bernard-Soulier syndrome. In this child, epistaxis was the major bleeding symptom. Despite massive substitutive therapy, the patient suffered several life-threatening episodes of hypovolaemic shock. Although epistaxis is not reported as a cause of death in patients with haemostasis defect, our case might suggest that in selected cases with inherited platelet defect and intractable epistaxis so severe as to make normal or near-normal life impossible, surgical treatment could be considered.

Adolescent↗
PubMedDate not supplied

Radical excision of a craniobasal tumor involving the middle cranial fossa. Technical note.

Craniobasal tumors affecting the middle cranial fossa are rarely treated radically; the main problem to solve is the presence of important nervous and vascular structures in this region. The Authors report a case of complete removal of a malignant tumor involving the temporal bone and the middle cranial fossa. Surgery was performed by the cooperation of the neurosurgical and the ENT teams.

Adult↗