Biomedical subjects

M Bertamini

Publications and source records attributed to M Bertamini.

6 recordsLinked to original sources

PubMed1998

Relative size perception at a distance is best at eye level.

Relative size judgments were collected for two objects at 30.5 m and 23.8 from the observer in order to assess how performance depends on the relationship between the size of the objects and the eye level of the observer. In three experiments in an indoor hallway and in one experiment outdoors, accuracy was higher for objects in the neighborhood of eye level. We consider these results in the light of two hypotheses. One proposes that observers localize the horizon as a reference for judging relative size, and the other proposes that observers perceive the general neighborhood of the horizon and then employ a height-in-visual-field heuristic. The finding that relative size judgments are best around the horizon implies that information that is independent of distance perception is used in perceiving size.

Analysis of Variance↗

PubMed1997

Detection of symmetry and perceptual organization: the way a lock-and-key process works.

We studied the speed with which observers could detect symmetry in drawings that incorporated symmetric contours--related by reflection or translation--within single objects or across different objects. We asked observers to perform a speeded decision whether pairs of contours are the same, i.e., related by reflection or by translation, or different. When the contours belong to a single object, observers are faster to see the relation between contours when they are related by reflection than by translation. When the contours belong to different objects, observers are faster to see the relation between the contours when they are related by translation than by reflection. We tested whether this advantage of translation is due to a lock-and-key process. We first tested our hypothesis by manipulating the correspondence of the features, so as to make matching more difficult. This change did not produce the predicted pattern of results. We performed a second manipulation to change the appearance of the objects: we increased the prägnanz of the objects by changing the type of lines used to connect the contours. Results indicate that perceptual organization can alter detectability of symmetry.

Female↗

PubMed1997

Amodal completion of partly occluded surfaces: is there a mosaic stage?

Recent investigators have proposed that amodal completion is a sequential process requiring a preliminary mosaic stage. Results of 6 studies of the time course of completion processes show support for this mosaic-first view with pictorial displays, but not with displays involving occlusion specified by binocular parallax or when pictorial displays were observed monocularly. These results still do not rule out the mosaic-first view. A parallel model, however, can account more economically for the available data.

Adult↗

PubMed1993

Memory for position and dynamic representations.

Memory for the position of an object is biased. When asked to judge whether an object has changed its position with respect to a position shown a few milliseconds before, observers tend to detect the displacement more often when the displacement is not in the expected direction (downward for a falling object). The hypothesis proposed by Freyd (1983, 1987) states that the internal representation of an object is intrinsically dynamic. Therefore, the forces perceived as acting on the object affect the representation. Quantitative predictions of this model were tested in three experiments by measuring memory distortion for the position of an object on an inclined plane. Angle of inclination and retention interval were varied. The results for different inclinations support the physical model. The time course of the memory distortion suggests a new view about the relation between this phenomenon and very short-term memory.

Adult↗

PubMed1990

Identifying contours from occlusion events.

Surface contours specified by occlusion events that varied in density, velocity, and type of motion (rotation or translation) were examined in four experiments. As a fourth experimental factor, there were both figure-motion trials (the occluding surface moved over a stationary background) and background-motion trials (the background moved behind a stationary surface) in each experiment. Displays contained line patterns and rotary motion (Experiment 1), line patterns and translatory motion (Experiment 2), textured surfaces and rotary motion (Experiment 3), and textured surfaces and translatory motion (Experiment 4). Results indicate that contour identifications are more accurate with translation than with rotation, and that background-motion trials are generally easier than figure-motion trials. Although density in all experiments affected identifications in both background- and figure-motion trials, velocity did so in Experiment 4 only. In Experiments 1, 2, and 3, velocity affected identifications in background-motion trials but not in figure-motion trials. In Experiments 3 and 4, the rate of accretion and deletion of texture was a poor predictor of identification accuracy. These results are not consistent with previous accounts of contour perception from occlusion events, and may reflect an involvement of ocular pursuit as a mechanism for registering contour information.

Adult↗

PubMed1988

Perceptual alternations in stereokinesis.

When a flat ellipse is slowly rotated in the frontoparallel plane, two different 3-D percepts can be obtained: (i) a rigid circular disc tilting back and forth in 3-D space, and (ii) an elongated egg, slanted into 3-D space, whose end parts seem to be located at different distances from the observer and describe a circular trajectory with respect to the frontal plane. Under prolonged observation, the two 3-D percepts alternate in time, separated by brief intervals in which either the rotation of a rigid flat ellipse in the frontal plane or an amoeba-like distortion of a 2-D shape can be perceived. An experiment is reported in which the sequence of perceptual alternations was investigated. Results show that the 3-D disc is mostly preceded by impressions of elastic amoeba-like deformations, whereas the 3-D egg is mostly preceded by the percept of a rotating flat ellipse. Direct transitions from egg to disc are not as frequent as transitions from disc to egg. Results are discussed in relation to Braunstein and Andersen's hypothesis that phenomena of this sort might result from the stimulation of automatic mechanisms for perceiving size change (changing-size neutral channels).

Attention↗