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At least 1,189 records · Page 66Linked to original sources
PubMed1993

Detecting slant-in-depth of real trapezoidal and rectangular surfaces: moving-monocular viewing equivalent to stationary-binocular viewing.

Cues from binocularity and observer motion are often believed to be more important in perceiving depth than pictorial cues such as relative visual size and linear perspective. Both binocularity and motion are effective in simulated displays. However, for real stimuli evincing nonveridical pictorial cues, binocularity has been more effective than motion; sometimes motion has had an insignificant effect. This may reflect inadequate extent of motion, an assertion investigated in the present study. Two groups of observers determined whether rectangular and trapezoidal surfaces were slanted-in-depth under stationary-monocular (SM), stationary-binocular (SB), and moving-monocular conditions with 15-cm (15MM) and 25-cm (25MM) lateral head-motion extents according to group. The trapezoidal surfaces appeared as rectangular during SM viewing to mislead regarding slant. The effect of pictorial cues was substantially diminished during SB viewing whereas 15MM viewing was weak, 25MM was as effective as SB viewing. Comparison of the overall numbers of correct responses for the two groups indicated no contextual biasing.

Adult↗
PubMed1978

Comparison of normal and learning disabled children on a nonverbal short-term memory serial position task.

A serial recall task was used to compare performance of 15 normal and 15 learning disabled elementary school children matched on CA, IQ, and sex with two and three dimensional representations of nonverbal eight-point shapes. Two a priori assumptions were not supported: (a) no differences in recall were found between groups and (b) no differences in recall were found for either group using two or three dimensional stimuli. Three dimensional stimuli did facilitate visual rehearsal at the primacy position for both groups. Learning disabled children's performance was consistent with the mediation deficiency hypothesis found with normal children.

Child↗
PubMed1983

Tactual access and stimulus dimensionality as determinants of young children's identification and transformational questions.

Thirty-six preschool children were invited to look at a set of stimulus materials. One-third of the children were presented with three-dimensional materials that they were free to touch, one third with three-dimensional materials that they could not touch, and one-third with life-size photographs of the objects. Results revealed that the children in each group asked a similar number of questions to identify the names of the objects. However, children who could touch the objects asked the most "transformational" questions (e.g., questions involving broader speculations about the object's origin, function, and relation to other objects in the environment), while those who could not touch the objects asked the next most and those shown photos of the objects asked the least.

Child Development↗
PubMed2000

An experimental comparison of viewpoint-specific and viewpoint-independent models of object representation.

Four experiments that investigate the cognitive representation of objects in human observers are reported. Two broad classes of theory were examined: viewpoint-specific and viewpoint-independent models. The former postulate that the data structures underpinning object recognition correspond to discrete views and require additional processing to access them from unfamiliar viewpoints. The latter postulate data structures that are independent of any particular viewpoint and can be directly accessed from a wide range of viewpoints. Two experimental tasks were used: a sequential matching paradigm and a cognitive learning paradigm. Findings favour viewpoint-specific models over viewpoint-independent models.

Adult↗
PubMed2000

Visual perception of motion and 3-D structure from motion: an fMRI study.

Functional magnetic resonance imaging was used to study the cortical bases of 3-D structure perception from visual motion in human. Nine subjects underwent three experiments designed to locate the areas involved in (i) motion processing (random motion versus static dots), (ii) coherent motion processing (expansion/ contraction versus random motion) and (iii) 3-D shape from motion reconstruction (3-D surface oscillating in depth versus random motion). Two control experiments tested the specific influence of speed distribution and surface curvature on the activation results. All stimuli consisted of random dots so that motion parallax was the only cue available for 3-D shape perception. As expected, random motion compared with static dots induced strong activity in areas V1/V2, V5+ and the superior occipital gyrus (SOG; presumptive V3/V3A). V1/V2 and V5+ showed no activity increase when comparing coherent motion (expansion or 3-D surface) with random motion. Conversely, V3/V3A and the dorsal parieto-occipital junction were highlighted in both comparisons and showed gradually increased activity for random motion, coherent motion and a curved surface rotating in depth, which suggests their involvement in the coding of 3-D shape from motion. Also, the ventral aspect of the left occipito-temporal junction was found to be equally responsive to random and coherent motion stimuli, but showed a specific sensitivity to curved 3-D surfaces compared with plane surfaces. As this region is already known to be involved in the coding of static object shape, our results suggest that it might integrate various cues for the perception of 3-D shape.

Adult↗
PubMed2003

The processing of kinetic contours in the brain.

This work investigates whether the brain assigns special cortical areas for the processing of kinetic contours. In human imaging experiments, we compared the brain activity produced in the so-called 'kinetic occipital' area ('KO') when humans perceive shapes generated from kinetic boundaries or from equiluminant colors. 'KO' was activated whenever subjects perceived shapes, no matter how they were derived; it is therefore not specialized for the processing of kinetic contours. The application of independent component analysis (ICA) to imaging data obtained when subjects viewed 22 min of an action movie showed that the time course of activity in 'KO' correlates better with activity in area V3 than with activity in two adjacent areas, V5 and LO. We thus consider 'KO' to be part of the V3 family of areas, and use the terminology of Smith et al. (J Neurosci 18:3816-3830, 1998), to refer to it as area V3B. Recordings from orientation-selective cells in the macaque V3 complex show that the great majority have the same orientational specificity when tested with oriented lines generated from kinetic stimuli or from luminance differences. We conclude that there is no present evidence for a visual area specialized for the processing of kinetic contours in the primate visual brain.

Brain Mapping↗