The perceptual organization of dot lattices

Bravais (1850/1949) demonstrated that there are five types of periodic dot patterns (or lattices): oblique, rectangular, centered rectangular, square, and hexagonal. Gestalt psychologists studied grouping by proximity in rectangular and square dot patterns. In the first part of the present paper, I (1) describe the geometry of the five types of lattices, and (2) explain why, for the study of perception, centered rectangular lattices must be divided into two classes (centered rectangular andrhombic). I also show how all lattices can be located in a two-dimensional space. In the second part of the paper, I show how the geometry of these lattices determines their grouping and their multistability. I introduce the notion ofdegree of instability and explain how to order lattices from most stable to least stable (hexagonal). In the third part of the paper, I explore the effect of replacing the dots in a lattice with less symmetric motifs, thus creating wallpaper patterns. When a dot pattern is turned into a wallpaper pattern, its perceptual organization can be altered radically, overcoming grouping by proximity. I conclude the paper with an introduction to the implications of motif selection and placement for the perception of the ensuing patterns.     

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.     

Pyramid algorithms for perceptual organization

Multiresolution (orpyramid) approaches to computer vision provide the capability of rapidly detecting and extracting global structures (features, regions, patterns, etc.) from an image. The human visual system also is able to spontaneously (orpreattentively) perceive various types of global structure in visual input; this process is sometimes calledperceptual organization. This paper describes a set of pyramid-based algorithms that can detect and extract these types of structure; included are algorithms for inferring three-dimensional information from images and for processing time sequences of images. If implemented in parallel on cellular pyramid hardware, these algorithms require processing times on the order of the logarithm of the image diameter.     

Attention enhances apparent perceptual organization

Perceptual organization and selective attention are two crucial processes that influence how we perceive visual information. The former structures complex visual inputs into coherent units, whereas the later selects relevant information. Attention and perceptual organization can modulate each other, affecting visual processing and performance in various tasks and conditions. Here, we tested whether attention can alter the way multiple elements appear to be perceptually organized. We manipulated covert spatial attention using a rapid serial visual presentation task, and measured perceptual organization of two multielements arrays organized by luminance similarity as rows or columns, at both the attended and unattended locations. We found that the apparent perceptual organization of the multielement arrays is intensified when attended and attenuated when unattended. We ruled out response bias as an alternative explanation. These findings reveal that attention enhances the appearance of perceptual organization, a midlevel vision process, altering the way we perceive our visual environment.     

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.     

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.     

Optical defocusing reverses perceptual organization.

At a certain point during the defocusing of a reversible figure, the organization of the figure reversed unexpectedly, and the reversal seemed more abrupt than a spontaneous reversal. The critical point is approximately constant over time for a given subject, and a similar point occurs during refocusing. This phenomenon is discussed in terms of inhibition between competing neural structures.     

Color aftereffects contingent on perceptual organization

The present experiment demonstrated that (a) cognitive organizational factors influence an orientation-contingent color (McCollugh) aftereffect, and (b) adaptation to colored gratings affected the perceptual organization of a reversible figure. Following adaptation to colored gratings, color aftereffects were reported in only one of two organizations of a reversible figure, and the colors conformed to the subjective contours of the test pattern rather than exclusively to the regions defined by horizontal and vertical pattern elements. In addition, an organization of the reversible figure that segregated vertical and horizontal pattern elements was dominant subsequent to adaptation.     

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.     

The ecological approach to perception: the place of perceptual content

The kind of perceptual systems that human beings possess enables each of us to respond in highly adaptive deliberate ways that take into account the suitability of particular behaviors to what we are aware of ourself as experiencing perceptually here and now. In deciding what to do next under the perceived circumstances, content is the dimension of perceptual experience that we consult. For perceptual content is how whatever the perceiver is now having perceptual experience of is given in or taken by the respective perceptual experience. Perceptual content includes presentational content, which is all the ways that what you are perceptually experiencing may be appearing to you, and intentional content, which is all the ways that your stream of perceptual experience may take to be that of which you have perceptual awareness in the environment or self. Therefore, perceptual content must be distinguished from the intentional object of perceptual awareness, which is that property, event, or entity of which you have perceptual awareness. Gibson proposed that there is no perceptual content independent of the particular intentional objects that one perceptually apprehends, which are always part of the ecological environment. This externalization of perceptual content was due, no doubt, to Gibson's conception of perceptually apprehending anything at all as not mediated by awareness of anything else, such as something immanent in perceptual experience itself. However, perceptual content need not be, theoretically, a replacement for what the perceiver has perceptual awareness of. During straightforward perceiving, the perceiver does not have awareness of perceptual content but of parts of the ecological environment including the perceiver. Perceptual content is how the external intentional object perspectivally appears from moment to moment and how it is perceptually taken to be, veridically or not. Perceptual taking of an ecological property is always in one or another of the latter's instantiations, and perceptual taking of an ecological entity or event is always with properties. The perceptual intentional object's appearing in a particular manner is distinct from perceptually taking the intentional object. For example, an ecological property may be taken quite veridically yet through a flow of varying appearance. And even when the property appears in a constant way, perceptual awareness may take it differently from one moment to the next. For example, a perceiver may have visual awareness of a surface without noticing the surface's color-texture, though the color-texture may appear to the perceiver throughout looking at the surface, before and after he or she stops noticing the color-texture.(ABSTRACT TRUNCATED AT 400 WORDS)     

Sequential priming of 3-D perceptual organization

In four experiments, the effects of sequential priming on the perceptual organization of complex three-dimensional (3-D) displays were examined. Observers were asked to view stereoscopic arrays and to search an embedded subset of items for an odd-colored target while 3-D orientation of the stimuli was varied randomly between trials. Search times decreased reliably when 3-D stimulus orientation was unchanged on consecutive trials, indicating substantial sequential priming by 3-D stimulus layout. The priming was nonsensory and was independent of priming by additional stimulus characteristics. Finally, priming by 3-D layout was unaffected by observers' foreknowledge of display orientation. Results indicate that perceptual organization of 3-D stimuli is guided by a short-term trace of 3-D spatial relationships between stimuli.     

Object-based visual selective attention and perceptual organization

We report the results of four experiments that were conducted to examine both the representations that provide candidate entities available for object-based attentional selection and the influence of bottom-up factors (i.e., geometric and surface characteristics of objects) and top-down factors (i.e., context and expectancies) on the selection process. Subjects performed the same task in each of the experiments. They were asked to determine whether two target properties, a bent end and an open end of a wrench, appeared in a brief display of two wrenches. In each experiment, the target properties could occur on a single wrench or one property could occur on each of two wrenches. The question of central interest was whether a same-object effect (faster and/or more accurate performance when the target properties appeared on one vs. two wrenches) would be observed in different experimental conditions. Several interesting results were obtained. First, depending on the geometric (i.e., concave discontinuities on object contours) and surface characteristics (i.e., homogeneous regions of color and texture) of the stimuli, attention was preferentially directed to one of three representational levels, as indicated by the presence or absence of the same-object effect. Second, although geometric and surface characteristics defined the candidate objects available for attentional selection, top-down factors were quite influential in determining which representational level would be selected. Third, the results suggest that uniform connectedness plays an important role in defining the entities available for attention selection. These results are discussed in terms of the manner in which attention selects objects in the visual environment.     

Checkerboard-specific color aftereffects: A failure to find effects of perceptual organization

Two experiments investigated the effects of differing perceptual organizations of reversible figures on McCollough aftereffects. Experiment 1 used colored checkerboard inducing stimuli and achromatic grating test stimuli. While some subjects tended to organize the checkerboards into rows and/or columns and others to organize them into obliques, these variations did not result in differences in aftereffect direction or magnitude. Experiment 2 induced an aftereffect with colored gratings and tested with checkerboards, gratings, and a reversible concentric octagon pattern. Perceptual organization had no effect on results for checkerboards, but was related to aftereffect strength for the octagon pattern. Indirect evidence suggests that, in the latter case, differences in aftereffect strength may have influenced the perceived organization, rather than vice versa. Finally, regardless of the specific organization perceived, spontaneous viewing of all test stimuli produced stronger aftereffects than were found when subjects reorganized the pattern. This may have resulted from a viewing strategy associated with reorganization, since similarly small aftereffects were found when subjects concentrated their attention on a single pattern element.