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PubMed1982

Global visual processing for saccadic eye movements.

Four experiments are reported in which saccadic eye movements are examined when the eye moves to targets in peripheral vision which consist of two discrete stimuli. It is found that under a variety of conditions, the saccade amplitude is such that the saccade lands at an intermediate position between the stimuli. This result has been termed the global effect and is interpreted as an influence of the global target configuration on the saccade amplitude. It is suggested that this phenomenon may be explicable in terms of activity in an ensemble of cells with large receptive fields. The experiments demonstrate the global effect in the situations of rapid automatic tracking, scanning for target detail and comparison of target configurations. The effect depends in a systematic quantitative manner on the properties of the visual stimuli. This may be loosely described by saying the saccade is directed to the centre of gravity of the target configuration. The saccades are however in general directed closer to the near target than predicted by the geometric centre of gravity. Although the effect appears in a similar form in all the conditions tested, minor differences do occur. It is also shown that the effect shows a dependence on the latency of the saccade, being most pronounced for saccades with short latencies. It is suggested that this may be a consequence of the dynamics of visual information processing.

Eye Movements↗
PubMed1979

Accessing similarity and dimensional relations: effects of integrality and separability on the discovery of complex concepts.

A series of studies investigated how stimulus integrality and separability impact the cognitive accessibility of similarity and dimensional relations. A good deal of previous work has established that stimulus integrality and separability differentially determine perception; here, the question is whether they also have differential effects on conception. Are the principles that govern perception also principles that can be readily discovered in concept learning tasks? Is a similarity-based rule especially easy to abstract from integral stimuli and a dimensionally-based rule especially easy to abstract from separable stimuli? In Experiments 1 and 2, we measured the relative ease with which the two types of rules (similarity and dimensional) are discovered by adults with the two types of stimuli (integral and separable). In experiment 1, the two rules were made redundant and we asked which rule the subjects learned. In Experiment 2, one rule was made relevant and the other irrelevant, and we compared relative speeds of learning. The results from the studies led us to conclude (a) that dimensionally based rules are more accessible from separable than from integral stimuli; (b) that similarity-based rules are more accessible from integral than from separable stimul; and (c) that, in general, subjects have a bias to access dimensional relations in this type of task. Experiment 3 pursued an additional suggestion from Experiments 1 and 2 that the dimensional relations within integral stimuli are sometimes accessible, more so when larger interstimulus differences are encountered. In confirmation, Experiment 3 demonstrated that adult subjects are more successful in applying a dimensional rule to pairs of integral stimuli that differ by a small amount if they also have exposure to pairs of integral stimuli that differ by a large amount. In a later discussion, it was argued that such a finding is consistent with the notion that the "dimensions" of integral stimuli are merely arbitrary directions in the integral stimulus space, and some relevant pilot data to that effect were presented. Finally, Experiment 4 took up a developmental issue. Young children have sometimes produced perceptual responses governed by similarity relations when presented with stimuli that are separable for adults. Will they more readily access similarity-based or dimensionally-based relations from such stimuli in the concept learning tasks here? The results showed that both kindergarteners and fifth graders more readily access the dimensional relations. A final discussion integrated the findings from the several experiments, taking up the following issues: (a) the relation between the perception and the conception of stimulus relations and (b) the nonprimacy of the dimensional axes in the integral stimulus space.

Adult↗
PubMed1986

Apparent height of a stereokinetic cone is decreased by departure from circularity.

Subjects made judgements of the comparative height of the stereokinetic cones seen for pairs of rotating figures with varying eccentricity and ellipticity. For any given eccentricity, ellipticity of the figure reduced the apparent height, with narrow ellipses seeming to be shallower. The effect is attributed to an interaction in constancy scaling.

Humans↗
PubMed1996

Evidence for good recovery of lengths of real objects seen with natural stereo viewing.

Six experiments are described in which good performance of the task of matching the lengths of two stationary real objects, gnarled wooden sticks, under a variety of binocular viewing conditions, including variations in viewing distances was demonstrated. Relatively poor matching performance was observed when the sticks were viewed monocularly in oscillatory motion, or monocularly and stationary. The results suggest that stereo can support good representations of metric scene structure when length judgments of natural objects are required under (quasi-)natural viewing. The implications of these results for theories of structure from stereo and structure from motion are discussed.

Adolescent↗
PubMed2002

Perceptual behavior: recurrence analysis of a haptic exploratory procedure.

Various object properties are perceptible by wielding. We asked whether the dynamics of wielding differed as a function of the to-be-perceived property. Wielding motions were analyzed to determine if they differed under the intention to perceive or not perceive rod length (experiment 1), to perceive object height versus object width (experiment 2), and to perceive the length forward of where the rod was grasped versus the position of the grasp (experiment 3). Perceiving these different properties is known to depend on different components of the object's inertia tensor. Analyses of the subtle recurrent patterns in the phase space of the hand motions revealed differences in wielding across the different perceptual intentions. Haptic exploratory procedures may exhibit distinct exploratory dynamics.

Adult↗