Biomedical subjects

V Salvano-Pardieu

Publications and source records attributed to V Salvano-Pardieu.

3 recordsLinked to original sources

PubMed2000

Spatial factors of brightness illusion in the Ehrenstein figure.

The strength of brightness illusion in an Ehrenstein figure has been examined as a function of two variables--inducing line length and gap size--by a two-alternative forced-choice procedure. The results show an interaction between the two variables; the length of the inducers and gap size are both involved in the formation of the brightness illusion, with gap size as the stronger factor. A spatial limit (corresponding to a gap size of 2.4 deg) was found, below which the illusion is always present regardless of the length of the inducers. An area ratio, defined as the ratio of the area of the ring formed by the four inducing lines of an Ehrenstein figure to the area of the illusory surface, takes into account the different spatial factors studied in the experiment and the global size of the Ehrenstein figure. The strength of the illusion was found to increase linearly with increasing values of the area ratio.

Adult↗

PubMed1998

Visual motion aftereffects: differential adaptation and test stimulation.

The local motion adaptation at the basis of the motion aftereffect (MAE) can be expressed in a variety of ways, depending upon the structure of the test display [Wade et al. (1996). Vision Research, 36, 2167-2175]. Three experiments are reported, which examined the characteristics of the test display and of the local adaptation process. In Experiment 1, MAEs were recorded in the central of three test gratings but their directions depended on the location of the centre relative to the adapting gratings. The effects of adapting motions in different directions were examined in Experiments 2 and 3, in which one or two adapting gratings were presented above or above and below a fixation cross. The upper grating always received the same (leftward) direction of motion during adaptation, and the lower grating was: moving in the opposite direction, stationary, moving in the same direction, or absent. The results indicate that no MAE is visible in the upper grating when a single test grating is observed experiment 2) and only occurs with two test gratings following differential adaptation between the upper and lower gratings (Experiment 3). Thus, the MAE occurs as a consequence of adapting restricted retinal regions to motion but it can only be expressed when differentially adapted regions are also tested.

Adaptation, Ocular↗

PubMed1996

Illusory form with inducers of opposite contrast polarity: evidence for multistage integration.

The perception of brightness differences in Ehrenstein figures and of illusory contours in phase-shifted line gratings was investigated as a function of the contrast polarity of the inducing elements. We presented either continuous lines or line-like arrangements composed of aligned dashes or dots whose spacing was varied. A yes/no procedure was used in which naive observers had to decide whether or not they perceived a brightness difference in a given Ehrenstein figure or an illusory contour in a phase-shifted line grating. The results show that brightness differences are perceived to some extent in Ehrenstein figures with inducers of opposite polarity of contrast; however, the percentage of yes response was systematically lower and response times were longer than for figures with inducers of the same polarity. Phase-shifted line gratings with lines of opposite polarity of contrast yielded stronger illusory contours and shorter response times than those with lines of the same polarity. When the sign of contrast was not the same within a given line of induction, neither differences in brightness nor illusory contours were perceived. The results suggest that the mechanisms that lead to apparent differences in brightness are more sensitive to input of the same contrast polarity, the mechanisms generating illusory contours more sensitive to input of opposite polarity. The data are discussed in the light of a multistage approach to illusory form perception and some implications for cortical models of illusory contour integration are discussed.

Adult↗