Biomedical subjects

Fulvio Domini

Publications and source records attributed to Fulvio Domini.

6 recordsLinked to original sources

PubMed2003

Recovering slant and angular velocity from a linear velocity field: modeling and psychophysics.

The data from two experiments, both using stimuli simulating orthographically rotating surfaces, are presented, with the primary variable of interest being whether the magnitude of the simulated gradient was from expanding vs. contracting motion. One experiment asked observers to report the apparent slant of the rotating surface, using a gauge figure. The other experiment asked observers to report the angular velocity, using a comparison rotating sphere. The results from both experiments clearly show that observers are less sensitive to expanding than to contracting optic-flow fields. These results are well predicted by a probabilistic model which derives the orientation and angular velocity of the projected surface from the properties of the optic flow computed within an extended time window.

Depth Perception↗

PubMed2003

Temporal integration of motion and stereo cues to depth.

In three experiments we investigated the integration of three-dimensional information provided over time by different depth cues. In the first experiment, we found that the perceptual derivation of surface orientation from the optic flow was affected by the prior presentation of static stereo information in the same spatial location. This bias weakened as the length of the motion sequence increased, but it was still present after 800 msec. In the second experiment, conversely, we found that the perceived orientation of a stereo-specified surface was not influenced by the prior presentation of a static stereo surface. In a third experiment, we found that two surfaces defined by identical disparity fields did not elicit the same perceived depth if, previously, one of them had been specified by a conjunction of stereo and motion information. This effect was found to last for at least 400 msec. Taken together, these findings indicate that interactions exist among different sources of depth information, even when they are provided at different moments of time.

Cues↗

PubMed2002

The conjunction of feature and depth information.

By inducing feature-contingent depth aftereffects, we show that the human visual system combines feature information with depth information. These contingent aftereffects were revealed through the use of a novel selective adaptation paradigm whose stimuli required the combination of feature and depth information in order to segment two interleaved, transparent surfaces. We argue that this combined processing exemplifies the remarkable resourcefulness of a visual system that has adapted to exploit conjunctions of cues that can aid in the segmentation of visual surfaces.

Adaptation, Biological↗

PubMed2002

Short-term temporal recruitment in structure from motion.

Temporal integration was investigated in the minimal conditions necessary to perform a structure-from-motion (SFM) task. Observers were asked to discriminate three-dimensional (3D) surface orientations in conditions in which the stimulus displays simulated velocity fields providing, in each frame transition, either sufficient (3 moving dots) or insufficient information (1 or 2 moving dots) to perform the task. When only two moving dots were shown in each frame transition of the stimulus displays (Experiment 1), we found that performance decreased as dot-lifetime increased. A facilitation effect of the overall display duration was also found. The negative effect of dot-lifetime on performance contrasts with what found in Experiment 2 with three dots in each frame transition, where performance improved with increasing dot-lifetime up to 170 ms, and then reached a plateau. Finally, for an optimal dot-lifetime of 150 ms, we found that performance was still above chance when each frame transition specified the motion of only one dot (Experiment 3). These results indicate that temporal recruitment alone can support the recovery of 3D information from sparse motion signals, thus providing a strong indication for the importance of temporal integration in the perceptual analysis of the optic flow. Our results reveal, moreover, that temporal integration in SFM has different characteristics, depending on whether, in each frame transition, the stimulus displays provide either sufficient (3 or more moving dots) or insufficient information (1 or 2 moving dots) to specify the higher-order properties of the optic flow necessary for 3D surface recovery.

Form Perception↗

PubMed2002

Illusory 3-D rotation induced by dynamic image shading.

Observers' perceptions of the three-dimensional structure of smoothly curved surfaces defined by patterns of image shading were investigated under varying conditions of illumination. In five experiments, observers judged the global orientation and the motion of the simulated surfaces from both static and dynamic patterns of image shading. We found that perceptual performance was more accurate with static than with dynamic displays. Dynamic displays evoked systematic biases in perceptual performance when the surface and the illumination source were simulated as rotating in opposite directions. In these conditions, the surface was incorrectly perceived as rotating in the same direction as the illumination source. Conversely, the orientation of the simulated surfaces was perceived correctly when the frames making up the apparent-motion sequences of the dynamic displays were presented as static images. In Experiment 6, moreover, the results obtained with the computer-generated displays were replicated with solid objects.

Adult↗

PubMed2002

Temporal integration in structure from motion.

A temporal integration model is proposed that predicts the results reported in 4 psychophysical experiments. The main findings were (a) the initial part of a structure-from-motion (SFM) sequence influences the orientation evoked by the final part of that sequence (an effect lasting for more than 1 s), and (b) for oscillating SFM sequences, perceived slant is affected by the oscillation frequency and by the sign of the final gradient. For contracting optic flows (i.e., rotations away from the image plane), the sequence with the lowest oscillation frequency appeared more slanted; for expanding optic flows (i.e., rotations toward the image plane), the sequence with the highest oscillation frequency appeared more slanted.

Humans↗