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PubMed1989

Perception of three-dimensional structure from optic flow without locally smooth velocity.

A common assumption in several analyses of optic flow is that the velocity field must be locally smooth in order to recover relative depth and the structure of surfaces in the environment. This study investigated the appropriateness of this constraint to human perception. In the first experiment, subjects were asked to identify the number of planes present in a display simulating one, two, three, four, or five overlapping, transparent planes. Subjects were able to detect the presence of up to three planes accurately for both horizontal and depth translations. In the second experiment, subjects' judgments of the depth separation of two transparent, overlapping planes increased with the simulated separation. In Experiment 3, subjects were able to determine accurately the sign of depth for two overlapping, transparent surfaces. These results suggest that a smoothness constraint is not required for the analysis of optic flow by human observers. Alternative approaches to the analysis of optic flow are discussed.

Acceleration↗

PubMed1990

Moon illusion in pictures: a multimechanism approach.

The existence of the moon illusion in pictorial representations was demonstrated in 6 experiments. Ss either judged the size of the moon in pictures, depicted as on the horizon or high in the sky, or drew horizon and elevated moons. The horizon moon was consistently judged to be larger than the elevated moon, independent of the angle at which the pictures are viewed. The distance paradox usually observed with the moon illusion (horizon moon apparently closer than the elevated moon) also exists in pictures. The magnitude of both size and distance effects depends on the salience of depicted depth cues. The pattern of results suggests that the moon illusion is caused by several interacting mechanisms and that use of pictorial stimuli may allow the separation of various cognitive from physiological contributions to the illusion.

Attention↗

PubMed1994

Time course of inhibition in color-response and word-response versions of the Stroop task.

Translation models of the Stroop effect predict inhibition when the relevant stimulus type does not match the response type, but a lack of inhibition when it matches. All 4 combinations of relevant stimulus type (color or word) and response type (color or word) were evaluated at several stimulus onset asynchronies (SOAs) in a button-pressing version of the Stroop task to assess this prediction. Inhibition was greatest when the relevant stimulus type did not match the response type. However, in contrast to predictions of translation models, color and word responses produced different patterns of inhibition and facilitation over SOA, implying differences in the word-to-color and color-to-word translation mechanisms, and inhibition was obtained in both of the color-response tasks. A modification of the translation model is proposed that incorporates a translation mechanism and accommodates special characteristics of word processing.

Color Perception↗

PubMed1997

On the statistical independence of color and shape in object identification.

M. J. Nissen (1985) showed that color and shape are processed independently. M. A. Monheit and J. C. Johnston (1994) argued that dependence of color and shape in these experiments was reduced due to random guessing. They conducted 4 experiments in which they attempted to reduce the effect of random guessing. A strong dependence of color and shape reports was observed. In this article the effects that random guessing can have on statistical (in)dependence are analyzed. The authors argue that Monheit and Johnston's analysis is incorrect and inconsistent with the data they report and that random guessing can be the cause of statistical dependence of color and shape reports.

Attention↗

PubMed1997

Dependence by any other name smells just as sweet: reply to van der Velde and van der Heijden (1997)

The hypothesis that people selectively attend to entire objects predicts that all attributes of an object will be reported either very accurately (if the object was attended) or very inaccurately (if it was unattended). Hence, reports of object attributes should show positive dependence. M. Monheit and J. Johnston (1994) have confirmed this prediction. F. van der Velde and A. H. C. van der Heijden (1997), however, have argued that dependence in the overall data is spurious. They advocate a model that partitions the data into 2 subsets, 1 for perception trials and 1 for guessing trials, each of which separately exhibits independence. Here, the authors argue that this treatment of guessing is misguided because, in effect, guesses are discarded rather than treated as failures of perception. The Monheit and Johnston analysis, on the other hand, is fundamentally sound and demonstrates precisely the kind of dependence predicted by the spatial attention hypothesis.

Attention↗

PubMed1998

Connectedness and the integration of parts with relations in shape perception.

Seven experiments investigated whether part connectedness would facilitate the perception of spatial relations among object parts. Experiments 1-4 showed that objects composed of connected parts are easier to distinguish from distractors in rapid serial visual presentation sequences than objects composed of separated parts and that this effect cannot be attributed to the presence of local features in the connected images. Experiments 5 and 6 revealed that image-based connectedness is neither necessary nor sufficient for the connectedness effect, and Experiment 7 showed that the connectedness effect is not a simple feature conjunction effect (i.e., it does not hold in a shape-color conjunction search task). These findings are consistent with the claim, central to the structural description theories, that the visual system not only decomposes objects into parts but also explicitly integrates those parts with their spatial relations.

Adult↗

PubMed2001

Visual representation of malleable and rigid objects that deform as they rotate.

Most studies and theories of object recognition have addressed the perception of rigid objects. Yet, physical objects may also move in a nonrigid manner. A series of priming studies examined the conditions under which observers can recognize novel views of objects moving nonrigidly. Observers were primed with 2 views of a rotating object that were linked by apparent motion or presented statically. The apparent malleability of the rotating prime object varied such that the object appeared to be either malleable or rigid. Novel deformed views of malleable objects were primed when falling within the object's motion path. Priming patterns were significantly more restricted for deformed views of rigid objects. These results suggest that moving malleable objects may be represented as continuous events, whereas rigid objects may not. That is, object representations may be "dynamically remapped" during the analysis of the object's motion.

Analysis of Variance↗

PubMed2002

Ideomotor compatibility in the psychological refractory period effect: 29 years of oversimplification.

Four experiments examined whether the psychological refractory period (PRP) effect can be eliminated with ideomotor compatible (IM) but not stimulus-response compatible (SR) tasks, as reported by A. G. Greenwald and H. G. Shulman (1973). Their tasks were used: a left or right movement to a left- or right-pointing arrow (IM) or to the word left or right (SR) for Task 1; saying "A" or "B" (IM) or "1" or "2" (SR) to an auditory A or B for Task 2. The stimulus onset asynchronies were 0, 100, 200, 300, 500, and 1,000 ms in Experiment 1, and only 0, 100, 200, and 1,000 ms in Experiments 2-4. The arrow was in the center of the screen in Experiments 1-3 and to the left or right in Experiment 4. As in Greenwald and Shulman's Experiment 2, the instructions stated that most often the 2 stimuli would be presented simultaneously. A PRP effect was obtained in all conditions, most likely because response-selection decisions are required even for IM tasks.

Acoustic Stimulation↗

PubMed1978

An investigation of the cues responsible for figure impossibility.

Two different perceptual confrontations produced by two different cues (sides that seem to twist and apparent levels of depth), which were thought to influence the perception of the degree of possibility of impossible torus figures, were examined in two experiments. In Experiment 1 it was found that net change in depth experienced with one scan around the figure was inversely related to magnitude estimates of possibility, whereas the number of apparently twisted sides was not. These results were verified in Experiment 2, a replication of Experiment 1 using stereograms of the figures, in which an interpretation of multiple levels of depth was more difficult.

Cues↗

PubMed1978

Visual images preserve metric spatial information: evidence from studies of image scanning.

Four experiments demonstrated that more time is required to scan further distances across visual images, even when the same amount of material falls between the initial focus point and the target. Not only did times systematically increase with distance but subjectively larger images required more time to scan than did subjectively smaller ones. Finally, when subjects were not asked to base all judgments on examination of their images, the distance between an initial focus point and a target did not affect reaction times.

Distance Perception↗

PubMed1978

Organizational factors in perceived dimensionality.

The hypothesis that perceived dimensionality of projection drawings is influenced by perceived organization was tested in two experiments. Organization was biased by coloration: The drawings were (a) uncolored, (b) colored in ways that emphasized plausible three-dimensional parts of the represented objects, or (c) colored in ways that emphasized two-dimensional (2D) parts of the drawings themselves. In Experiment 1, subjective ratings of three-dimensionality (3D) were greater for the 3D-biased stimuli than for the unbiased stimuli, and ratings for the 2D-biased stimuli were lower than for the unbiased stimuli. Similar results were obtained in Experiment 2 in which latencies to perceive the drawings three-dimensionally were measured. The 3D-biased stimuli were seen in depth more quickly than the unbiased stimuli, and the 2D-biased stimuli were seen in depth more slowly than the unbiased stimuli. Additional results on the relation between ratings and latencies suggest that latencies are affected more strongly by object complexity than are ratings.

Color Perception↗

PubMed1978

Multidimensional same--different judgments: evidence against independent comparisons of dimensions.

Commonly discussed models of performance in the multidimensional same-different task are based on the assumption that independent same-different decisions are reached for each of the stimulus dimensions used in an experiment. In these models, a higher level mechanism examines th outcome of these independent decisions in order to determine whether the stimuli are the same or different overall. Previous evidence indicating that these models are inconsistent with results from same trials is summarized, and a new test of the above assumption using data from different trials is proposed. Detailed analysis of reaction times from different trials is shown, at least for some pairs of dimensions, to be incompatible with the view that separate same-different decisions are reached for each dimension. The major finding is that there are more relatively fast responses in a condition with two dimensions different, compared with the two conditions with only one of the dimensions different, than any processing model treating the dimensions separately could predict. The results suggest that partial information may be combined across dimensions in order to reach a "different" judgment.

Color Perception↗

PubMed1980

Mental imagery and the third dimension.

What sort of medium underlies imagery for three-dimensional scenes? In the present investigation, the time subjects took to scan between objects in a mental image was used to infer the sorts of geometric information that images preserve. Subjects studied an open box in which five objects were suspended, and learned to imagine this display with their eyes closed. In the first experiment, subjects scanned by tracking an imaginary point moving in a straight line between the imagined objects. Scanning times increased linearly with increasing distance between objects in three dimensions. Therefore metric 3-D information must be preserved in images, and images cannot simply be 2-D "snapshots." In a second experiment, subjects scanned across the image by "sighting" objects through an imaginary rifle sight. Here scanning times were found to increase linearly with the two-dimensional separations between objects as they appeared from the original viewing angle. Therefore metric 2-D distance information in the original perspective view must be preserved in images, and images cannot simply be 3-D "scale-models" that are assessed from any and all directions at once. In a third experiment, subjects mentally rotated the display 90 degrees and scanned between objects as they appeared in this new perspective view by tracking an imaginary rifle signt, as before. Scanning times increased linearly with the two-dimensional separations between objects as they would appear from the new relative viewing perspective. Therefore images can display metric 2-D distance information in a perspective view never actually experiences, so mental images cannot simply be "snapshot plus scale model" pairs. These results can be explained by a model in which the three-dimensional structure of objects is encoded in long-term memory in 3-D object-centered coordinate systems. When these objects are imagined, this information is then mapped onto a single 2-D "surface display" in which the perspective properties specific to a given viewing angle can be depicted. In a set of perceptual control experiments, subjects scanned a visible display by (a) simply moving their eyes from one object to another, (b) sweeping an imaginary rifle sight over the display, or (c) tracking an imaginary point moving from one object to another. Eye-movement times varied linearly with 2-D interobject distance, as did time to scan with an imaginary rifle sight; time to tract a point varied independently with the 3-D and 2-D interobject distances. These results are compared with the analogous image scanning results to argue that imagery and perception share some representational structures but that mental image scanning is a process distinct from eye movements or eye-movement commands.

Cues↗

PubMed1982

Density versus feature weights as predictors of visual identifications: comment on Appelman and Mayzner.

Appleman and Mayzner's application of the distance-density model to confusion data is compared with Keren and Baggen's application of the feature-matching model. In both applications, the distinctive features of two stimuli are predictors of the number of confusion errors. However, the models differ in that the feature-matching model assigns weights to the features and assumes that the shared feature weights also affect the probability of confusion. In contrast, the distance-density model assumes that the number of confusions between two stimuli is affected by the number of stimuli in the entire stimulus set that are similar to the two stimuli (density). The two models are compared in the context of a set of digit identification data.

Discrimination Learning↗

PubMed1982

Application of geometric models to letter recognition: distance and density.

This article reviews studies in which a single letter is visually presented under adverse conditions and the subject's task is to identify the letter. The typical results for such studies are (a) certain pairs of letters are more often confused than other pairs of letters; (b) certain letters are more easily recognized than others; and (c) confusion errors for a letter pair are often asymmetric, the number of errors differing depending on which letter of the pair is presented as the stimulus. A geometric model incorporating the properties of distance and spatial density (after Krumhansl) is presented to account for these results. The present application of the distance-density model assumes that each letter is constructed in a typical 5 X 7 dot matrix. Each letter is represented in 35-dimensional space based on its constituent dots. A central idea behind the model, embodied in the property of spatial density, is that an explanation of typical results must take into account the relationship of the entire stimulus set to both the presented letter and the responded letter. Specifically, according to the model, (a) pairs of letters that are close in geometric space are more often confused than pairs of letters that are distant; (b) letters that are in less spatially dense regions are more easily recognized than letters that are in more spatially dense regions; and (c) asymmetric confusion errors result when one member of a letter pair is in a denser region than the other member of the letter pair. The distance-density model is applied to published and unpublished results of the authors as well as published results from two other laboratories. Alternative explanations of the three typical letter recognition results are also considered. The most successful alternative explanations are (a) confusions are an increasing function of the number of dots that two letters share; (b) letters constructed from fewer dots are easier to recognize; and (c) asymmetries arise when one member of a letter pair is more easily recognized, since that letter then has fewer confusion errors to give to the other letter of the pair. The model is discussed in terms of the distinction between template matching and feature analysis. An alternative classification of letter recognition models is proposed based on the global versus local qualities of features and the spatial information associated with each feature. The model is extended to explain reaction time study results. It is suggested that the distance-density model can be used to create optimal letter fonts by minimizing interletter confusions and maximizing letter recognizability.

Discrimination Learning↗

PubMed1985

Size illusion, distance illusion, and terrestrial passage: comment on reed.

Two assumptions of Reed's (1984) terrestrial passage theory are questioned. First, Reed assumes that the moon's failure to increase in visual subtense while elevating is accounted for strictly by perceptual distancing. This allows a formal account of the moon distance illusion, but at the expense of a compelling explanation of the moon size illusion. Second, in order to explain the distance illusion, Reed assumes that all objects, regardless of their perceived altitude, are perceived to start from a common point at the horizon. Several alternative application of Reed's terrestrial-passage foundation to the actual illusions are suggested.

Astronomical Phenomena↗

PubMed1987

Piecemeal organization and cognitive components in object perception: perceptually coupled responses to moving objects.

In three experiments, observers who were instructed to perceive one of two alternative depth arrangements of a three-dimensional wire cube fixated near one of two intersections that differed in the degree to which they specified the cube's veridical depth organization. In order to separate perceptual effects from experimenter effects, we measured indirect reports about variables perceptually coupled to perceived depth rather than direct reports about perceived depth. In all three experiments, reversal durations at the two intersections differed, even though the two were parts of a single object. In addition, reversals varied with viewers' intentions. Thus, the unit of perceptual organization may be smaller than the entire object, and viewers' intentions can influence the perception of real moving objects. In additional analyses, reversal durations were separated into two components: nonelective instability and malleability; the question of whether these two components of ambiguity are functionally distinct could not be decided.

Depth Perception↗

PubMed1988

Minimodularity and the perception of layout.

In natural vision, information overspecifies the relative distances between objects and their layout in three dimensions. Directed perception applies (Cutting, 1986), rather than direct or indirect perception, because any single source of information (or cue) might be adequate to reveal relative depth (or local depth order), but many are present and useful to observers. Such overspecification presents the theoretical problem of how perceivers use this multiplicity of information to arrive at a unitary appreciation of distance between objects in the environment. This article examines three models of directed perception: selection, in which only one source of information is used; addition, in which all sources are used in simple combination; and multiplication, in which interactions among sources can occur. To monocular spatial information, using all combinations of the presence or absence of relative size, height in the projection plane, occlusion, and motion parallax. Visual stimuli were computer generated and consisted of three untextured parallel planes arranged in depth. Three tasks were used: one of magnitude estimation of exocentric distance within a stimulus, one of dissimilarity judgment in how a pair of stimuli revealed depth, and one of choice judgment within a pair as to which one revealed depth best. Grouped and individual results of the one direct and two indirect scaling tasks suggest that perceivers use these sources of information in an additive fashion. That is, one source (or cue) is generally substitutable for another, and the more sources that are present, the more depth is revealed. This pattern of results suggests independent use of information by four separate, functional subsystems within the visual system, here called minimodules. Evidence for and advantages of minimodularity are discussed.

Attention↗