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PubMed1998

Infants' perception of object unity in translating and rotating displays.

In 3 experiments, the authors examined the sensitivity of infants to the unity of a partly occluded moving rod undergoing translation, rotation, or oscillation. Four-month-old infants were sensitive to the unity of the partly occluded rod when it translated, but not when it rotated, behind an occluder. Six-month-old infants perceived the rotating rod as continuing behind the occluder, but they did not perceive the unity of a rod that oscillated back and forth behind the occluder. Finally, 6-month-old infants showed an ambiguous response to a rotating rod when the shape of the occluder was changed from rectangular to round. These findings suggest that all types of common motion are not equivalent for specifying infants' perceptions of occluded objects. Additional factors should be considered that take into account the information specified by different types of motion and by different conditions at the intersection of the occluder and the object.

Attention↗
PubMed1992

Global shape cannot be attended without object identification.

Whether the global shape of objects can be processed without accessing semantic or identity information was tested. Ss judged which of 2 fragmented forms had the same global shape as a reference stimulus. Matching stimuli could be physically identical, semantically related, or unrelated. The reference stimulus and nonmatching (distractor) form could be semantically related or unrelated. Similarity effects in the related condition were unconfounded with matches nameable and nonnameable forms. For nameable forms, related matching forms facilitated performance; a related distractor disrupted performance. Semantic interference was eliminated when nameable distractors were replaced with nonnameable partners; semantic similarity effects on matching were eliminated with a nonnameable reference stimulus and with inverted targets and distractors. Access to information concerning global shape does not normally occur without object identification.

Adult↗
PubMed1995

Competing global and local completions in visual occlusion.

In visual occlusion 2 amodal-completion tendencies occur frequently. One tendency leads toward the simplest completed shape (a global completion) and the other to a shape for which the completion itself is as simple as possible (a local completion). Two experimental paradigms were used to test the strengths of these completion tendencies: a drawing task and a simultaneous matching task. The experimental results support the notion that the preference for either a global or a local completion is the consequence of a competition between interpretations. Finally, the authors discuss how the preference for a completion can be predicted by a model that is based on a quantification of both global and local aspects.

Adult↗
PubMed1978

Perception and masking of wholes and parts.

These exerpiments show that the effects of masking on reports of target lines depend on the context in which the target lines appear. Subjects viewed brief presentations of target lines either alone or in drawings of three-dimensional objects, and each target display was preceded and followed by one of several different mask stimuli. There were two main findings: (a) A mask containing a haphazard array of lines interfered more with single lines than it did with lines in objects. (b) A mask containing drawings of the object displays interfered more with lines in objects than did either of two control masks containing relatively flat, less coherent patterns. In a control condition, the object mask interfered slightly less with reports of single lines than either of the control masks did. The discussion considers how the effects obtained here bear on models of the processing of wholistic stimuli and their component parts.

Discrimination, Psychological↗
PubMed1981

Coding theory of visual pattern completion.

It is possible to construct a line drawing that represents one object partly hidden behind another, and most subjects complete the interrupted figure and see the hidden object as whole. This article is addressed to two problems: (a) What are the necessary and sufficient conditions for such figural completion to occur, and (b) exactly what will be seen behind the occluding figure---that is, what completion will be made? Leeuwenberg's coding model for line drawings was used to analyze a number of such figures, along with the hypothesis that figural completion occurs whenever it results in a simplification of final code of the whole figure. Data from previous experiments along with results from two new experimental studies were collected and shown to agree with this hypothesis. Of various possible figural completions or "mosaic" interpretations, subjects chose the ones resulting in the simplest overall code. However, the above conclusions are correct only if "simple" is precisely defined as the smallest information load in a completely reduced code. Other possible theories of figural completion, both structuralist and Gestalt, may invoke familiarity, particular "cues," like T-shaped intersections, simplicity of the hidden figure, symmetry, and good continuation. All such possibilities were considered in the experiments and shown to fail, wrongly predicting at least one figure. The coding-theory analysis, on the other hand, made correct predictions for all of the 25 figures used.

Cues↗
PubMed1984

The effect of changes in visible area on facial recognition.

The proportion of a human face which needs to be visible for correct identification was investigated. Photographs of familiar public faces were presented under two conditions: (i) the facial photographs were original photographs with local information; and (ii) the facial photographs were blurred, with high spatial frequencies removed and with no local information. Subjects could scan the face as they wished through a moveable window generated by a TV system and had to identify the depicted person as quickly as possible. Window size was varied systematically. The main study showed that, in spite of including only its local features, a familiar facial photograph could be perfectly identified when the visual window covered one-fifth of the whole face, and that a global image of the whole face was obtained when nearly half of the whole face was processed simultaneously. The structure of the memory image of the face is discussed in the light of the results obtained.

Adult↗
PubMed1990

Sensitivity to the displacement of facial features in negative and inverted images.

Subjects have previously been reported to show difficulties in recognising faces which are either inverted or in photographic negative. Experiments are reported in which a two-alternative forced-choice technique was used to measure sensitivity for distinguishing faces which have been modified by having the eyes moved vertically or horizontally. Subjects were less sensitive to such changes for inverted faces or negative faces, and were even less sensitive for faces that were both inverted and negative. No such effects were found for a control stimulus consisting simply of three solid circles in the same positions as the eyes and mouth of a face. When the stimuli consisted of eyes, nose, and mouth, but without a surround, no evidence of inversion or negation effects was found, which suggests that a facial surround is necessary. When the stimulus consisted of a facial surround with the eyes, nose, and mouth replaced by solid circles, effects of negation were found, but no effects of inversion. This dissociation of the effects of negation and inversion may suggest that they are the result of different underlying mechanisms.

Adult↗
PubMed1994

Local and global minima in visual completion: effects of symmetry and orientation.

The visual information that specifies three-dimensional objects is often incomplete because objects occlude parts of themselves and other objects. Yet people rarely have difficulty perceiving complete, three-dimensional forms. Somehow the visual system seems to 'complete' partially specified objects. The perceptual processes underlying this seemingly effortless and immediate completion are poorly understood. Sekuler and Palmer designed in 1992 the primed-matching paradigm for the objective study of completion effects and their microgenesis. Results from the paradigm suggest that global processes may play a role early in perceptual completion, and that local processes dominate only under limited conditions of figural regularity and orientation. These results are not consistent with purely local or purely global theories of completion. The findings have implications for object perception and representation.

Attention↗
PubMed1994

Angular induction as a function of the length and position of segments and gaps.

The perceptual distortions which are manifested in the Poggendorff illusion can be studied with the use of a more restricted set of stimulus elements. Experiments were designed in which angular induction effects between two line elements, known respectively as the test segment and induction segment, were evaluated. In some stimulus configurations the induction 'segment' consisted of a tandem pair of segments. Previous studies had shown that the induction segment will bias operant judgments of collinearity for a test segment, this effect being a function of the relative angle between the two. Six experiments are reported, in which the length and position of segments in relation to the tip of the test segment were varied. It was found that substantial induction is produced by a very short segment, and that this can bias judgment even when its displacement spans more than 10 deg of visual angle. Several aspects of the data suggest that the strength of effect is a log-linear function of segment position. However, the results from displacement of single or tandem segments do not conform to predictions based on length/response summation, and thus do not support a linear-systems approach. Neural substrates for these interactions are given brief attention.

Adult↗
PubMed1995

The theory of the curvature-constraint line for amodal completion.

Amodal completion of partly occluded figures is analyzed as natural computation. Here amodal completion is shown to consist of four subproblems: representation, parsing, correspondence, and interpolation. Second, each problem is shown to be basically solvable on the basis of the generic-viewpoint assumption. It is also argued that the interpolation problem might be the key problem because of mutual interdependence among the subproblems. Third, a theory is described for the interpolation problem, in which the generic-viewpoint assumption and the curvature-consistency assumption are presumed. The generic-viewpoint assumption entails that the orientation and the curvature should not change at the point of occlusion. The curvature-consistency assumption entails that the hidden contour should have the minimum number of inflections to maintain continuity in orientation and curvature. The shape of the interpolated contour represented qualitatively in terms of the number of inflections can uniquely be determined when the location of the terminators and local orientation and curvature of the visible contours at the terminators are given. Fourth, it is shown in an instant psychophysics that the theory is highly consistent with human performance.

Adult↗
PubMed1995

Solving occlusion indeterminacy in chromatically homogeneous patterns.

Overlapping figures can produce consistent depth stratification even when chromatically homogeneous. Since neither T-junctions nor X-junctions are present in these patterns, the problem arises of what rules determine the direction of depth stratification, ie which surfaces appear in front and which behind. In a series of demonstrations and formal experiments involving perception of stereopsis, motion, transparency, motion in depth, and reversible figures, the validity of the principle that the visual system tends to minimise the formation of interpolated modal contours was tested. The reason why larger surfaces tend to be seen modally in front, rather than behind, would reflect the geometrical property that when, in overlapping objects, larger surfaces are closer there will be shorter occluding boundaries than when smaller surfaces are closer. It is shown that this constraint is independent of the empirical depth cue of relative size. An example is also given of a simple computational strategy that extracts, from chromatically homogeneous patterns, occluding subjective contours corresponding to those perceived by human observers.

Attention↗
PubMed1996

Spatial context in recognition.

In recognizing objects and scenes, partial recognition of objects or their parts can be used to guide the recognition of other objects. Here, the role of individual objects in the recognition of complete figures and the influence of contextual information on the identification of ambiguous objects were investigated. Configurations of objects that were placed in either proper or improper spatial relations were used, and response times and error rates in a recognition task were measured. Two main results were obtained. First, proper spatial relations among the objects of a scene decrease response times and error rates in the recognition of individual objects. Second, the presence of objects that have a unique interpretation improves the identification of ambiguous objects in the scene. Ambiguous objects were recognized faster and with fewer errors in the presence of clearly recognized objects compared with the same objects in isolation or in improper spatial relations. The implications of these findings for the organization of recognition memory are discussed.

Adult↗
PubMed2006

Surface assignment modulates object formation for visual short-term memory.

Recent results have suggested that the operational units of visual short-term memory (VSTM) are whole objects, rather than features or the total amount of information to be remembered. Here, for the first time, the influence of surface assignment on object formation for VSTM was investigated. The observers had to memorize the features of four briefly presented (300 ms) two-part objects, followed by a mask and a cue indicating which object to report on. The experiments contrasted whether there were any apparent depth differences between the two parts of each object, and whether observers had to report on only one or both features of the post-cued target object. Depth differences induced with stereoscopic disparity, and with a pictorial depth cue (simple interposition of object features), interfered strongly with performance when both features of an object needed to be memorized, but aided performance when only a single feature needed to be remembered. Furthermore, there was considerable within-feature interference consistent with some previous findings, but contradicting others. The potential implications for conceptions of VSTM are discussed in the light of two hypothesized stages: an early feature-based stage, as well as a higher-level object-based stage where the depth manipulations exert their effects. The results argue for a strong modulatory influence of surface assignment on object formation for a VSTM task.

Attention↗
PubMed1979

The influence of stroke on visual illusion magnitude.

In an attempt to resolve contradictory reports about the effect of right-versus left-hemisphere damage on perception of the Mueller-Lyer illusion, the present study examined judgments of stroke patients using this and several other visual illusions. The results provide some indication of abnormal perception of the Mueller-Lyer by patients with left-hemisphere damage. But the overall magnitude of illusion was normal in both groups of patients. It is possible that stroke damage did not affect the brain areas that are responsible for "gestalt" synthesis. However other recent studies using the Mueller-Lyer suggest that actual or incipient eye movements play an important role in the perception of this illusion, and under some conditions of testing, it is the activity of the left hemisphere that determines illusion magnitude.

Brain Mapping↗
PubMedDate not supplied

Object recognition by component features: are there age differences.

This study extended aspects of Biederman's (1987) recognition-by-components (RBC) theory to the analysis of age differences in the recognition of incomplete visually-presented objects. RBC theory predicts that objects are recognizable or recoverable under conditions of fragmentation if a sufficient amount of essential structural information remains available. Objects are rendered nonrecoverable by the omission or obstruction of essential structural features at vertices and areas of concavity. Fifteen young adults and 15 older adults participated in a study of the effects of amount (25%, 45%, 65%) and type of fragmentation (recoverable, nonrecoverable) on object naming. Age-related declines in recognizing incomplete objects were associated with the amount of fragmentation, but type of fragmentation did not affect the performance of older adults. For the young adults, accuracy of performance was affected by both amount and type of fragmentation, consistent with Biederman's RBC theory. These results were interpreted as suggesting that age-related declines in perceptual closure performance have to do with non-structural factors such as the ability to inferentially augment degraded or missing visual information.

Adolescent↗
PubMed2003

Global transsaccadic change blindness during scene perception.

Each time the eyes are spatially reoriented via a saccadic eye movement, the image falling on the retina changes. How visually specific are the representations that are functional across saccades during active scene perception? This question was investigated with a saccade-contingent display-change paradigm in which pictures of complex real-world scenes were globally changed in real time during eye movements. The global changes were effected by presenting each scene as an alternating set of scene strips and occluding gray bars, and by reversing the strips and bars during specific saccades. The results from two experiments demonstrated a global transsaccadic change-blindness effect, suggesting that point-by-point visual representations are not functional across saccades during complex scene perception.

Adult↗
PubMed2002

Ecological statistics of Gestalt laws for the perceptual organization of contours.

Although numerous studies have measured the strength of visual grouping cues for controlled psychophysical stimuli, little is known about the statistical utility of these various cues for natural images. In this study, we conducted experiments in which human participants trace perceived contours in natural images. These contours are automatically mapped to sequences of discrete tangent elements detected in the image. By examining relational properties between pairs of successive tangents on these traced curves, and between randomly selected pairs of tangents, we are able to estimate the likelihood distributions required to construct an optimal Bayesian model for contour grouping. We employed this novel methodology to investigate the inferential power of three classical Gestalt cues for contour grouping: proximity, good continuation, and luminance similarity. The study yielded a number of important results: (1) these cues, when appropriately defined, are approximately uncorrelated, suggesting a simple factorial model for statistical inference; (2) moderate image-to-image variation of the statistics indicates the utility of general probabilistic models for perceptual organization; (3) these cues differ greatly in their inferential power, proximity being by far the most powerful; and (4) statistical modeling of the proximity cue indicates a scale-invariant power law in close agreement with prior psychophysics.

Form Perception↗