Rethinking perceptual organization: The role of uniform connectedness

A principle of perceptual organization, calleduniform connectedness (UC), is described, and a theoretical approach to perceptual organization is proposed in which this principle plays a fundamental role. The principle of UC states that closed regions of homogeneous properties—such as lightness, chromatic color, texture, and so forth—tend to be perceived initially as single units. We demonstrate its effects and show that they occur even when opposed by powerful grouping principles such as proximity and similarity. We argue that UC cannot be reduced to such grouping principles, because it is not a form of grouping at all. We then propose a theoretical framework within which UC accounts for the initial (orentry level) organization of the visual field into primitive units. Classical principles of grouping operate after UC, creating superordinate units consisting of two or more basic-level units. Parsing processes also operate after UC, dividing basic-level units into subordinate parts. UC in the retinal image is proposed to be a necessary, but not a sufficient, condition for unit formation, since connected elements on the retina that are perceived to lie in separate depth planes fail to be perceived as units. This fact, together with other evidence that the Gestalt principles of grouping are based onperceived (rather than retinal) relations, suggests that the organization of visual stimulation into UC objects is ultimately achieved within a relatively late, postconstancy representation of environmental surfaces. The implications of this possibility are discussed in light of present theories of visual perception.     

The role of transparency in perceptual grouping and pattern recognition.

The shortest stimulus exposure time for which transparency can be seen was examined. In the first experiment, overlapping digits were presented for 120 ms and the luminance in the overlapping regions was varied. Subjects reported, in separate blocks of trials, either the apparent transparency of the digits or the identity of the digits. When the luminance was set so that one set of digits appeared to be seen through the other, recognition of the digits was high. When the luminance in the overlapping regions did not produce impressions of transparency, digit recognition was low. In the second experiment, digit identification at several stimulus durations was compared between stimuli that had luminance that was valid for transparency and stimuli that had invalid luminance. Performance was found to be higher in the valid luminance condition than in the invalid condition after as little as 60 ms exposure duration. This result suggests that the impression of transparency requires only relatively short exposure durations.     

On the figural after-effect

Two experiments were carried out on the figural after-effect. The first was intended to discover whether the figural after-effect did in fact take place with statistically significant universality. The method of scoring is relevant to the question of statistical significance, but at the best the figural after-effect appears to occur in only a slightly significant manner under the first conditions used. These involved the viewing of a single circle displaced to the left of a fixation point (the inspection-figure) and so placed that if it were superimposed on the second figure—which consisted of two squares on either side of the fixation-point—the circle completely encircled the left-hand square. The second figure is called the test-figure. The fixation point of the inspection-figure was fixated for 25 seconds with one eye, and then the test-figure was substituted and viewed with the opposite eye. A decision was then given by the observer as to the relative size of the squares. Eye-dominance did not appear to be connected with these after-effect processes.

In the second experiment, however, the statistical significance of the occurrence of the after-effects was undoubted. There were two changes in experimental conditions: the instructions to the observers were changed somewhat and a second circle was introduced into the inspection-figure. No difference of any kind was found to occur in the figural after-effect when the test-figure and inspection-figure were displaced horizontally and when they were displaced veitically, and there appeared to be a precisely opposite effect to that predicted when the test-figure and the inspection-figure were actually superimposed.

The most important finding was that, whereas in the first experiment the after-effect occurred with a frequency which was barely significant statistically, it occurred on every occasion under the different conditions of the second experiment.     

Toward a perceptual theory of transparency

Theories of perceptual transparency have typically been developed within the context of a physical model that generates the percept of transparency (F. Metelli's episcotister model, 1974b). Here 2 fundamental questions are investigated: (a) When does the visual system initiate the percept of one surface seen through another? (b) How does it assign surface properties to a transparent layer? Results reveal systematic deviations from the predictions of Metelli's model, both for initiating image decomposition into multiple surfaces and for assigning surface attributes. Specifically, results demonstrate that the visual system uses Michelson contrast as a critical image variable to initiate percepts of transparency and to assign transmittance to transparent surfaces. Findings are discussed in relation to previous theories of transparency, lightness, brightness, and contrast-contrast.     

The topological approach to perceptual organization

To address the fundamental question of “what are the primitives of visual perception”, a theory of topological structure and functional hierarchy in visual perception has been proposed. This holds that the global nature of perceptual organization can be described in terms of topological invariants, global topological perception is prior to the perception of other featural properties, and the primitives of visual form perception are geometric invariants at different levels of structural stability. In Part I of this paper, I will illustrate why and how the topological approach to perceptual organization has been advanced. In Part II, I will provide empirical evidence supporting the early topological perception, while answering some commonly considered counteraccounts. In Part III, to complete the theory, I will apply the mathematics of tolerance spaces to describe global properties in discrete sets. In Part IV, I will further present experimental data to demonstrate the global-to-local functional hierarchy in form perception, which is stratified with respect to structural stability defined by Klein's Erlangen Program. Finally, in Part V, I will discuss relations of the global-to-local topological model to other theories: The topological approach reformulates both classical Gestalt holism and Gibson's direct perception of invariance, while providing a challenge to computational approaches to vision based on the local-to-global assumption.     

The role of perceptual organization in the depth perception of kinetic lattice displays

College student subjects were asked to judge perceived depth in computer-generated displays. In all displays, one lattice of points moved through a stationary lattice in either a rowwise or columnwise direction. No points of the two lattices ever touched. Two display variables, strain and shear, each had a significant effect on depth ratings. Shear, however, was only effective at the level of strain for which depth ratings were high. The results confirm earlier studies in which “topological breakage” information was found to affect depth perception. The outcome of this study suggests that principles of perceptual organization can influence the nature of effective breakage information.     

The role of learning experience on the perceptual organization of Chinese characters

The effect of learning experience on the perceived graphemic similarity of Chinese characters was examined by comparing results of the constrained (Experiment 1) and unconstrained (Experiment 2) shape-sorting tasks obtained from various groups of participants with different learning experiences and ages. The results from hierarchical cluster analysis showed that both Taiwanese and Japanese undergraduates classified characters in relation to their configurational structures, whereas American undergraduates, Taiwanese illiterate adults, and kindergartners categorized characters based on strokes or components. Although a trend of developmental changes from local details to more globally defined patterns was found, the identification of structure as consistently perceived by skilled readers has to be nourished by learning experience and cannot be obtained solely through maturation.     

Orientation relative to the retina determines perceptual organization

Two experiments are reported which show that perceptual unit formation, as measured by Gillam’s method of using common reversals of ambiguous lines as an index of their coherence, depends strongly on the orientation of the configuration. Measurements under conditions of 90° head and body tilt show that the critical orientation is retinal, not physical. The results are discussed in relation to other findings and to possible explanations.     

Cognitive architecture of perceptual organization: from neurons to gnosons

What, if anything, is cognitive architecture and how is it implemented in neural architecture? Focusing on perceptual organization, this question is addressed by way of a pluralist approach which, supported by metatheoretical considerations, combines complementary insights from representational, connectionist, and dynamic systems approaches to cognition. This pluralist approach starts from a representationally inspired model which implements the intertwined but functionally distinguishable subprocesses of feedforward feature encoding, horizontal feature binding, and recurrent feature selection. As sustained by a review of neuroscientific evidence, these are the subprocesses that are believed to take place in the visual hierarchy in the brain. Furthermore, the model employs a special form of processing, called transparallel processing, whose neural signature is proposed to be gamma-band synchronization in transient horizontal neural assemblies. In neuroscience, such assemblies are believed to mediate binding of similar features. Their formal counterparts in the model are special input-dependent distributed representations, called hyperstrings, which allow many similar features to be processed in a transparallel fashion, that is, simultaneously as if only one feature were concerned. This form of processing does justice to both the high combinatorial capacity and the high speed of the perceptual organization process. A naturally following proposal is that those temporarily synchronized neural assemblies are “gnosons”, that is, constituents of flexible self-organizing cognitive architecture in between the relatively rigid level of neurons and the still elusive level of consciousness.     

Heterosocial perceptual organization: application of the choice model to sexual coercion

Luce's (1959, 1963) choice model was used to characterize individual differences in men's perception of women's affect as friendly, sexually interested, sad, or rejecting. Women's clothing styles were associated with differences in the model's parameters. Sensitivity to sadness, rejection, and friendliness declined when women were dressed provocatively, whereas sensitivity to sexual interest increased. Provocative clothing was also associated with an increased bias to assume that positive affect was sexual interest rather than friendliness. Men at risk for perpetrating sexual aggression were less sensitive to women's affect than low-risk men were. They were also more likely than low-risk men to associate provocative clothing with sexual interest, and conservative clothing with friendliness. Results indicate that heterosocial perception may help to predict sexually coercive behavior and may be an important target for intervention.     

Learning perceptual organization in infancy

It has been demonstrated that older infants (6- to 7-month-olds), but not younger infants (3- to 4-month-olds), use form similarity to organize stimuli consisting of X and O elements. We investigated whether utilization of form similarity is governed by maturation or experience by contrasting how infants perform when familiarized with a single exemplar versus multiple exemplars depicting a particular organization. In Experiment 1, 3- to 4-month-olds failed to organize alternating columns or rows of squares and diamonds or Hs and Is, respectively. In Experiment 2, same-aged infants familiarized with all three patterns (X-O, square-diamond, H-I) displayed evidence of organization. The results suggest that 3- to 4-month-olds can use form similarity to organize visual patterns in a concept-formation task. The findings imply that perceptual organization based on form similarity is learned through experience with multiple patterns depicting a common arrangement, rather than immediately apprehended in an individual pattern.     

Asynchrony tolerance in the perceptual organization of speech

Researchers have claimed that listeners tolerate large temporal distortion when integrating the spectral components of speech. In some estimates, perceivers resolve linguistic attributes at spectral desynchronies as great as the duration of a syllable. We obtained new measures of perceptual tolerance of auditory asynchrony, using sine-wave synthesis in order to require perceivers to resolve the speech stream dynamically. Listeners transcribed sentences in which the tone analogue of a second formant was desynchronized relative to the remaining tones of a sentence, with desynchrony ranging from a 250-msec lead to a 250-msec lag. Intelligibility declined symmetrically from 72% at synchrony to 7% at 6100 msec. This finding of narrow asynchrony tolerance indicates a time-critical feature of the auditory perceptual organization of speech