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PubMed1980

Stimulus-rule interactions in concept verification.

The difficulty of learning a conceptual rule has been shown to depend upon the stimulus attributes which that rule conjoins. For what appear to be separable attributes, the disjunctive rule is easier than the conjunctive. In contrast, for what appear to be integrable attributes, the conjunctive rule is easier. This paper reports six experiments designed to determine whether the integrality of stimulus attributes affects the speed of verification of the stimulus, as positive or negative, with respect to a given conjunctive or disjunctive concept. The pattern of reaction times is not consistent with the result of rule-learning experiments and does not support an integrality hypothesis. Verification times seem to be more a function of the perceptual salience of the relevant attributes of the concept. Thus, a perceptual-integrality hypothesis is an unlikely explanation of rule learning results.

Color Perception↗
PubMed1996

Weight perception and the haptic size-weight illusion are functions of the inertia tensor.

The complex effects of mass and volume on weight perception (e.g., the size-weight illusion) were hypothesized to follow simply from invariants of rotational dynamics. In Experiments 1-3, the rotational inertia of wielded, occluded objects was varied independently of mass, size, and torque. Perceived heaviness depended only on rotational intertia. Reanalysis of J. C. Stevens and L. L. Rubin's (1970) study revealed that size's influence on weight perception depends on specific patterns of the eigenvalues of the inertia tensor. These patterns were simulated in Experiments 4-6 with objects of fixed mass, volume, and visible size. Perceived heaviness decreased and increased, respectively, over object sets with the eigenvalue patterns of (a) constant mass, increasing volume and (b) increasing mass, constant volume. Weight perception and the size-weight illusion depend on stimulus invariants, not inference.

Female↗
PubMed1985

Spatial interactions in the rhesus monkey retina: a behavioural study using the Westheimer paradigm.

For two trained rhesus monkeys, increment thresholds for a small test-spot of 100 ms duration were determined as a function of background size, at 10 retinal eccentricities along the horizontal meridian. Typical 'Westheimer-functions' were obtained, i.e. threshold first increases with increasing background size, reaches a maximum, then decreases with further increasing backgrounds and finally reaches a plateau. With increasing retinal eccentricities, the position of the peak of the functions is shifted towards larger background sizes, indicating an increase of perceptive field centre size from 0.25 degrees at 5 degrees eccentricity to 1.5 degrees at 40 degrees eccentricity. The perceptive field centres tend to be slightly smaller in the nasal retina. Total perceptive field sizes, as indicated by the beginnings of the plateaus, increase from about 1 degree near the fovea to about 3 degrees at 40 degrees eccentricity. The perceptive field centre sizes of two human observers, tested under the same experimental conditions, closely resemble those of the monkeys. The total perceptive fields are larger in the human subjects. The retinal ganglion cells determining threshold in this experiment are most likely the broad-band cells. The agreement between the behaviourally determined perceptive field centre sizes and the receptive field centre sizes of broadband cells (measured by DeMonasterio and Gouras 1975) is excellent. The dendritic fields of P-alpha-ganglion cells, most likely the morphological substrates of the broad-band cells (Perry, Oehler and Cowey 1984) are somewhat smaller at all eccentricities.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

The interaction of oculomotor cues and stimulus size in stereoscopic death constancy.

In the natural world, observers perceive an object to have a relatively fixed size and depth over a wide range of distances. Retinal image size and binocular disparity are to some extent scaled with distance to give observers a measure of size constancy. The angle of convergence of the two eyes and their accommodative states are one source of scaling information, but even at close range this must be supplemented by other cues. We have investigated how angular size and oculomotor state interact in the perception of size and depth at different distances. Computer-generated images of planar and stereoscopically simulated 3-D surfaces covered with an irregular blobby texture were viewed on a computer monitor. The monitor rested on a movable sled running on rails within a darkened tunnel. An observer looking into the tunnel could see nothing but the simulated surface so that oculomotor signals provided the major potential cues to the distance of the image. Observers estimated the height of the surface, their distance from it, or the stereoscopically simulated depth within it over viewing distances which ranged from 45 cm to 130 cm. The angular width of the images lay between 2 deg and 10 deg. Estimates of the magnitude of a constant simulated depth dropped with increasing viewing distance when surfaces were of constant angular size. But with surfaces of constant physical size, estimates were more nearly independent of viewing distance. At any one distance, depths appeared to be greater, the smaller the angular size of the image. With most observers, the influence of angular size on perceived depth grew with increasing viewing distance. These findings suggest that there are two components to scaling. One is independent of angular size and related to viewing distance. The second component is related to angular size, and the weighting accorded to it grows with viewing distance. Control experiments indicate that in the tunnel, oculomotor state provides the principal cue to viewing distance. Thus, the contribution of oculomotor signals to depth scaling is gradually supplanted by other cues as viewing distance grows. Binocular estimates of the heights and distances of planar surfaces of different sizes revealed that angular size and viewing distance interact in a similar way to determine perceived size and perceived distance.

Adult↗
PubMed1998

An analysis of perceptions from changes in optical size.

The allocation of perceived size and perceived motion or displacement in depth resulting from retinal size changes (changes in the visual angle of the stimulus) was investigated in situations in which all other cues of perceived changes in distance were absent. The allocation process was represented by the size-distance invariance hypothesis (SDIH), in which, for a given change in visual angle, the perceived depth was determined only by the amount of size constancy available. The changes in perceived size and perceived distance (perceived depth) were measured by kinesthetic observer (open-loop) adjustments in five situations. These situations consisted of optical expansions or contractions presented successively or simultaneously or as a mixture of successive and simultaneous presentations. The amounts of perceived motion or perceived displacement in depth obtained by kinesthetic measures were compared with those obtained from size constancy measures as applied to the SDIH. This latter measure accounted for more of the perceived depth obtained from simultaneous and mixed situations than it did for the perceived depth from the successive situations and more for the perceived depth obtained from the expansion than from the contraction situations, whether these were simultaneous or mixed. Perceived rigidity of the stimulus (perfect size constancy) clearly was not obtained in any of the situations. Significant partial size constancy and some predictive ability of the perceived sagittal motion was found using the SDIH in all the situations except in the successively presented contraction situation, with the predictive ability from the SDIH increasing with increases in the amount of size constancy. The difference between the observer's measures of the perceived motion or displacement in depth and the amount of perceived motion or displacement predicted from the perceptions of linear size using the SDIH is asserted to be due to a cognitive process associated with the perception of the different stimulus sizes as off-sized objects.

Humans↗