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This study examined whether the perception of heading is determined by spatially pooling velocity information. Observers were presented displays simulating observer motion through a volume of 3-D objects. To test the importance of spatial pooling, the authors systematically varied the nonrigidity of the flow field using two types of object motion: adding a unique rotation or translation to each object. Calculations of the signal-to-noise (observer velocity-to-object motion) ratio indicated no decrements in performance when the ratio was .39 for object rotation and .45 for object translation. Performance also increased with the number of objects in the scene. These results suggest that heading is determined by mechanisms that use spatial pooling over large regions.

Two experiments were undertaken to determine the manner of age-related differences in visual motion processing. The first experiment quantified the difference of lamellar flow from age across the visual field while the second experiment detected radial flow. Results showed that there was a significant difference in human motion detection system between younger and older adults. Older women manifested decline for the detection of lamellar flow.

Most theoretical approaches to perception of heading rely on the directions of image velocity vectors as the primary source of heading information. The research described in this article examined an additional source of information for determining heading: distributions of image velocity magnitudes. Displays simulated observer motion relative to rigid three-dimensional environments. Depth was distributed nonuniformly such that image velocity magnitudes provided, for some display conditions, conflicting heading information relative to the radial directions of the flow field. Results indicated that image velocity magnitudes influenced heading performance, suggesting that the perception of heading is not based solely on the radial structure of the directions of image flow.

An assumption central to the study of 3-dimensional (3-D) shape perception is that sufficient information must be present to detect a 3-D surface. Three experiments were conducted to determine the variables important for the detection of 3-D surfaces from optic flow. Observers were presented with optic-flow displays simulating either points positioned on a corrugated 3-D surface or points randomly positioned within a 3-D volume. The task of the observer was to indicate whether the display appeared to be a 3-D surface. An increase in frequency of the corrugation for simple (single-frequency corrugation) surfaces resulted in a decrease in surface detection. Detection performance increased with an increase in density and amplitude for both simple and complex (multiple-frequency corrugation) surfaces. An analysis of the deformation of the displays suggests that 3-D surface detection may be based on the summed absolute value of the 2 shear components of deformation.

We examined the ability of younger and older adults to selectively process moving items and ignore stationary items in a task that required the search for a target defined by a conjunction of movement and form (i.e., search for a moving X among moving Os and stationary Xs) in displays of 5, 9, 17, and 25 stimuli (Experiment 1) and displays of 5, 10, and 20 stimuli (Experiment 2). We also investigated subjects' performance in two feature search tasks, the search for a target defined by movement or form. Finally, we examined the influence of practice on feature and conjunction search. Younger and older adults searched the displays at similar rates in the feature and conjunction search tasks. Older and younger adults also benefited equivalently from practice. These data suggest age-equivalence in the processes which underlie feature search in dynamic environments as well as those processes responsible for the segregation of moving and stationary objects in the visual field.

Some of the abilities that change with age include the ability to detect 3-dimensional surfaces and the ability to distinguish motion coherence of two-dimensional images. Two groups of old and young adults were tested for visual acuity in perceiving whether the images presented corresponded to a random velocity pattern of a corrugated or a flat surface. Variances in performance were more marked among the group of aged subjects that in the younger group.

In 3 experiments the authors examined the effects of surface shape on the detection of surfaces in structure from motion displays. In Experiment 1 they found the number of points necessary to distinguish simple quadratic surfaces from points randomly placed in a volume to be low, in the range of 4-6 points. In Experiment 2 they found that a hyperbolic shape is harder to detect than an arch or parabolic shape and that more curved shapes are easier to detect than less curved shapes. In Experiment 3 they found that detection of sinusoidal shapes increases with increasing amplitude and decreasing frequency, confirming previous results with motion parallax displays. This pattern of results is consistent with a model in which triangular surface patches are fit through adjacent triples of points and displays with smaller mean orientation changes between neighboring triangles are judged to be surface displays.