Simultaneity constancy

Sound and light take different amounts of time to reach their respective receptors, to be transduced, and to be transmitted to the cortex. Their processing times also vary with factors such as intensity and retinal eccentricity. We assessed the capability of subjects to perceive simultaneity correctly despite these variations. Temporal asynchronies of up to 200 ms were introduced between the components of sound/light pairs. Using the method of constant stimuli, seven subjects judged which came first. Distance, and hence the times of arrival of paired visual and auditory targets, was varied from 1 to 32 m. Visual intensity was varied by viewing the target through 1.8 dB attenuating glasses, and a retinal eccentricity of 20 degrees was compared to central presentation. Despite large differences in reaction times, which varied in a predictable way with the stimulus parameters, the timing of sound/light pairings judged as simultaneous corresponded to when the light and sound left the source simultaneously. Almost complete compensation was found in all conditions tested, showing that these substantial but predictable variations in timing can be taken into account in creating simultaneity constancy.     

Speed constancy as a function of size constancy

If perceived velocity were to be a function of phenomenal extent traversed per unit time, speed constancy would be derivable from size constancy. Experiments were performed to test this possibility in which visible frames of reference were eliminated. With cues to distance, judgments ofspeed approached constancy; without such cues, judgments of speed were in terms of rate ofimage displacement.     

Direction constancy

A series of experiments investigating the constancy of perceived direction was conducted. Experiments 1, 2, and 3 indicated that the perception of direction, while close to constancy, exhibited a consistent departure from constancy of approximately 2.5 deg. Experiments 4 and 5 investigated the departure from constancy in terms of the information of the position of the eyes within the head and the information of the retinal area (local sign) being stimulated. The results of these experiments indicated that the departure from constancy was a function of the underestimation of the position of the eyes within the head.     

Transparent layer constancy

Perceived transparency was studied as a constancy problem. In the episcotister (E-) model of scission, luminances are partitioned into layer and background components; four luminances determine values of two layer parameters that specify constancy of a transparent layer on different backgrounds. The E-model was tested in an experiment in which 12 Ss matched 24 pairs of four-luminance patterns by adjusting two luminances of the comparison pattern. Both the standard and the comparison were perceived as a transparent layer on a checkerboard. The E-model predicts matches when layer values are identical in the two patterns. One parameter was constant, constraining the adjustment along the second dimension. Obtained values corresponded well with E-predictions. Alternative models based on local luminance or average contrast ratios accounted for less variability. Results indicate that transparency models should utilize luminance, not reflectance, as the independent variable.     

Routes to object constancy: Implications from neurological impairments of object constancy

Previous studies have established the existence of neurological impairments of object constancy: the ability to recognize that an object has the same structure across changes in its retinal projection. Five case studies of brain-damaged patients with deficits in achieving object constancy are reported. To test object constancy, patients discriminated two photographs of a target object, taken from different views, from a photograph of a visually similar distractor object. Four patients showed impaired matching only when the principal axis of the target object in one photograph was foreshortened. The fifth patient showed impaired matching only when the saliency of the target object's primary distinctive feature was reduced. This double dissociation suggests that normally there may be two independent means of achieving object constancy: one by processing an object's local distinctive features, the other by describing the object's structure relative to the frame of its principal axis. Neurological damage can selectively impair either process. Further, this impairment can be independent of deficits in processing visual form, since two patients with a selective deficit in the foreshortened matching task showed relatively normal form discrimination. The patient dependent on local distinctive feature information showed a deficit in size discrimination. It is suggested that this patient fails to utilize global properties of form. This failure may underlie both his impairment in achieving object constancy and in processing certain dimensions of form.     

Photometric, geometric, and perceptual factors in illumination-independent lightness constancy

It has been shown that lightness constancy depends on the articulation of the visual field (Agostini & Galmonte, 1999). However, among researchers there is little agreement about the meaning of "articulation." Beyond the terminological heterogeneity, an important issue remains: What factors are relevant for the stability of surface color perception? Using stimuli with two fields of illumination, we explore this issue in three experiments. In Experiment 1, we manipulated the number of luminances, the number of reflectances, and the number of surfaces and their spatial relationships; in Experiment 2, we manipulated the luminance range; finally, in Experiment 3 we varied the number of surfaces crossed by the illumination edge. We found that there are two relevant factors in optimizing lightness constancy: (1) the lowest luminance in shadow and (2) the co-presence of patches of equal reflectance in both fields of illumination. The latter effect is larger if these patches strongly belong to each other. We interpret these findings within the albedo hypothesis.     

Color constancy and dispositionalism

This article attempts to do two things. The first is to make it plausible that any adequate dispositional view of color will have to associate colors with complex functions from a wide range of normal circumstances to a wide range of (simultaneously) incompatible color appearances, so that there will be no uniquely veridical appearance of any given color. The second is to show that once this move is made, dispositionalism is in a position to provide interesting answers to some of the most challenging objections that have been pressed against it. It explains why colors do not seem to “come on” when the lights come on, and why the right thing to say seems to be that the light causes the objects to reveal their colors. It explains why the content of visual experience need not be problematically circular. It eliminates the problem of intrapersonal variation in color appearance. And it even provides resources for dealing with the problem of interpersonal variation. It is true that in moving to the more complex view, the dispositionalist becomes subject to a new objection, which has been called “the problem of unity.” The paper offers a solution to this problem as well.     

Varieties of object constancy

Three experiments are described in which two pictures of isolated man-made objects were presented in succession. The subjects' task was to decide, as rapidly as possible, whether the two pictured objects had the same name. With a stimulus-onset asynchrony (SOA) of above 200 msec two types of facilitation were observed: (1) the response latency was reduced if the pictures showed the same object, even though seen from different viewpoints (object benefit); (2) decision time was reduced further if the pictures showed the same object from the same angle of view (viewpoint benefit). These facilitation effects were not affected by projecting the pictures to different retinal locations. Significant benefits of both types were also obtained when the projected images differed in size. However, in these circumstances there was a small but significant performance decrement in matching two similar views of a single object, but not if the views were different. Conversely, the object benefit, but not the viewpoint benefit, was reduced when the SOA was only 100 msec. The data suggest the existence of (at least) two different visual codes, one non-retinotopic but viewer-centred, the other object-centred.     

Proportionality,linearity, and parameter constancy: Messick and Sentis reconsidered

Messick and Sentis found greater support for weak proportionality in subjects' outcome allocations (suggesting that subjects wish to maintain a constant ratio between outcomes across situations when inputs are held constant) than for constant differences between outcomes. They claimed that their data thus provided stronger support for Adams' ratio definition of equity than for Harris' linear formula. A dialogue between the two sets of authors establishes that (1) so far as their specification of fair outcomes is concerned, Adams' formula is a special case of the linear formula; (2) weak proportionality does not necessarily follow from Adams' formula and can be derived from the linear formula; (3) Adams' formula applied to subjective (rather than experimenter-defined) inputs nevertheless provides a more natural base from which to derive weak proportionality than does the linear formula in its general form; (4) excellent fits to several sets of data, including much better fit to Messick and Sentis' data than that provided by weak proportionality, are obtained if we assume that subjects use allocations which are a weighted average of those implied by Adams' formula, the Equality principle, and Komorita and Kravitz' Equal Excess Norm; and (5) a fit to Messick and Sentis' data that is almost as good as that provided by the weighted solutions model is obtained by assuming that subjects apply Adams' formula to subjective inputs and subjective outcomes that are different from the corresponding experimenter-defined values. It is agreed that the delineation of the relationships among observable properties of outcome distributions, alternative equity formulae, and different psychological processes is as important as it can be devious.     

Oculomotor adjustments and size constancy

The effect on matched size of the oculomotor adjustments was determined by stimulation and relaxation of accommodation and convergence by means of spherical lenses. The normal coupling between accommodation and convergence was maintained by introducing the amount of convergence appropriate to the lens power and each S’s interpupillary distance. Data indicate that the oculomotor adjustments are adequate to account for size constancy up to approximately 1 m, beyond which their effect progressively decreases. The actual accommodation in force was assessed by means of the laser scintillation technique. It was determined that the magnitude of accommodation responds accurately to the spherical lens introduced up to about 1 m observation distance, beyond which underaccommodation was noted. Examination of the matched size as a function of the actual accommodation distance reveals a very close correspondence to the size constancy prediction up to about 1 m.     

Shape constancy from novel views

Prior experiments on shape constancy from novel views are inconclusive: Some show that shapes of objects can be recognized reliably from novel views, whereas others show just the opposite. Our analysis of prior results suggests that shape constancy from novel views is reliable when the object has properties that constrain its shape: The object has volumetric primitives, it has surfaces, it is symmetrical, it is composed of geons, its contours are planar, and its images provide useful topological information about its three-dimensional structure. To test the role of some of these constraints, we performed a set of experiments. Solid shapes (polyhedra) were shown on a computer monitor by means of kinetic depth effect. Experiment 1 showed that shape constancy can be reliably achieved when a polyhedron is represented by its contours (most of the constraints are present), but not when it is represented by vertices or by a polygonal line connecting the vertices in a random order (all the constraints are absent). Experiments 2 and 3 tested the role of individual constraints. Results of these experiments show that shape constancy from novel views is reliable when the object has planar contours and when the shapes of the contours together with topological information about the relations among the contours constrain the possible interpretations of the shape. Symmetry of the object and the topological stability of its image also contribute to shape constancy.     

Impossible shadows and lightness constancy

The intersection between an illumination and a reflectance edge is characterised by the 'ratio-invariant' property, that is the luminance ratio of the regions under different illumination remains the same. In a CRT experiment, we shaped two areas, one surrounding the other, and simulated an illumination edge dividing them in two frames of illumination. The portion of the illumination edge standing on the surrounding area (labelled contextual background) was the contextual edge, while the portion standing on the enclosed area (labelled mediating background) was the mediating edge. On the mediating background, there were two patches, one per illumination frame. Observers were asked to adjust the luminance of the patch in bright illumination to equate the lightness of the other. We compared conditions in which the luminance ratio at the contextual edge could be (i) equal (possible shadow), or (ii) larger (impossible shadow) than that at the mediating edge. In addition, we manipulated the reflectance of the backgrounds. It could be higher for the contextual than for the mediating background; or, vice versa, lower for the contextual than for the mediating background. Results reveal that lightness constancy significantly increases when: (i) the luminance ratio at the contextual edge is larger than that at the mediating edge creating an impossible shadow, and (ii) the reflectance of the contextual background is lower than that of the mediating one. We interpret our results according to the albedo hypothesis, and suggest that the scission process is facilitated when the luminance ratio at the contextual edge is larger than that at the mediating edge and/or the reflectance of the including area is lower than that of the included one. This occurs even if the ratio-invariant property is violated.