Biomedical subjects

D Zavagno

Publications and source records attributed to D Zavagno.

3 recordsLinked to original sources

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

The glare effect and the perception of luminosity.

The impression of self-luminosity in the glare effect was studied in two experiments. In experiment 1 the target (CS) was set to the highest luminance of the field and subjects were asked to adjust the luminance ramp of the inducers (R) against five backgrounds (B) to the point where they began to see CS as self-luminous. It was found that there is a linear relationship between background and luminance ramp. Another group of subjects carried out the same task in experiment 2, but this time CS and R were linked together so that CS would always have the same luminance as the highest luminance level of R, as adjustments were performed. It was found that: (i) adjustments were always lower than the highest luminance available; (ii) the linear relationship between background and luminance ramp was confirmed; (iii) observers reported a compelling impression of self-luminous grays. Data are discussed in relation to Bonato and Gilchrist's model for the perception of luminosity. The authors advance the hypothesis that luminance ramps are used at an early stage of encoding for the perception of luminosity.

Contrast Sensitivity↗

PubMed1999

Some new luminance-gradient effects.

Three compelling luminance-gradient effects are described. The first effect concerns a brightness enhancement and a luminous mist spreading out from a central area having the same luminance as the white background and surrounded by four rectangular inducers shaded with a linear luminance gradient. The second effect is perceived with a photographically reversed configuration, and concerns what may be considered a brightness reduction or the enhancement of a darkness quality of a target area of the visual scene. The third effect concerns the perception of a self-luminous disk inside a somewhat foggy medium. The effects are worthy of further examination because they challenge current theories of luminosity perception and brightness perception in general.

Contrast Sensitivity↗