Perceptual organization of moving stimuli modulates the flash-lag effect.

When a visual stimulus is flashed at a given location the moment a second moving stimulus arrives at the same location, observers report the flashed stimulus as spatially lagging behind the moving stimulus (the flash-lag effect). The authors investigated whether the global configuration (perceptual organization) of the moving stimulus influences the magnitude of the flash-lag effect. The results indicate that a flash presented near the leading portion of a moving stimulus lags significantly more than a flash presented near the trailing portion. This result also holds for objects consisting of several elements that group to form a unitary percept of an object in motion. The present study demonstrates a novel interaction between the global configuration of moving objects and the representation of their spatial position and may provide a new and useful tool for the study of perceptual organization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Switching attention within and between objects: The role of subjective organization.

Provided a direct assessment of object-based allocation of attention through comparing different Ss' responses to the same stimulus patterns under different perceptual organizations. Eight undergraduates participated in each of 4 experiments. Exps 1A and 1B employed 2-object stimulus patterns to evaluate attention switching within and between objects while equating the number of intervening contours across conditions. Exps 2A and 2B used the same stimulus patterns, but varied the Ss perceptual organization such that these patterns were perceived as 1 object rather than 2. An object effect was found if a stimulus pattern was seen as a single object. The study provides converging evidence to the existence of multiple levels of visual representations. It suggests that attention selects the internal representation of both space and the object, and that subjective organization is an important factor in the manifestation of the object effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual grouping and spatial distortion: A developmental study.

20 Ss in each of 5 age groups (kindergartners; 2nd, 4th, and 6th graders; and graduate students) estimated distances between elements in patterns illustrating the Gestalt grouping principles of proximity, similarity, closure, and good continuation. Ss of all age groups consistently judged distances between elements in the same perceptual group as smaller than physically identical distances between elements in different perceptual groups, which indicated that all Ss were sensitive to the structure of the Gestalt patterns. The magnitude of these distance distortions decreased significantly with age, which suggests that perceptual development includes improvements in the ability to disregard Gestalt groupings when the task requires selective attention to certain elements. Results are consistent with evidence that perceptual development moves from visual processing based primarily on global attributes of patterns to processing that can selectively analyze the component structure of patterns. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Separability and integrality of global and local levels of hierarchical patterns.

Used a constrained classification task to examine the perceptual relations between global and local levels in hierarchical patterns composed of many, relatively small elements and those composed of few, relatively large elements. In 4 experiments, 52 18–35 yr olds made classifications based on form or texture or according to the shape of the configuration or the elements. Results indicate that configural and elemental levels were perceptually separable for many-element patterns when processed as form and texture. Ss could attend to either level without being affected by variation along the irrelevant dimension. However, when the same many-element patterns were processed for global and local shape. Ss could not selectively attend to either level. For few-element patterns, global configuration and local elements appeared to be perceptually integral dimensions. Results are discussed in terms of the global precedence hypothesis and explanations of integral and separable dimensions. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Geometric psychology generates the visual Gestalt.

Discusses an appropriate theoretical structure for the gestalt principles of visual form perception that is consistent with anatomical and neurophysiological knowledge and builds positively on it. It is suggested that much is known about the detailed psychophysics and physiology of mammalian visual systems, but there has been little study of the ways local processes in the visual system work cooperatively to produce the global phenomena of perception. The gestalt psychologists demonstrated perceptual organization but were hindered in their theorizing by the primitive knowledge at that time of how the brain operates and an inadequate model of cortical function. Recent discoveries in visual anatomy and physiology suggest that brain functions can be modeled in terms of one or more differentiable topological structures. Discussed are the visual manifold; holonomy, integrability, and visual contours; transversality and the principle of transverse control; interlude; and relation to the visual gestalt. It is concluded that (1) all the elements of a differential geometric structure can be identified within the primary visual processing system and (2) the major gestalt laws of perceptual organization follow naturally from the mathematical structure. (French abstract) (4 p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual units in the acquisition of visual categories.

A series of experiments provided evidence that the representational structure of categories comprising dot patterns is based on pattern parts and pattern configuration rather than on pattern elements. Similarity judgments and postacquisition classification data could not be explained in terms of element-level perceptual units, even for categories of dot patterns with 7 of their 8 dots in the exact same relative location. The importance of higher order perceptual units was indicated by evidence that long-term retention of information specific to previously learned category exemplars, which is typical of natural objects, can also be obtained for artificial dot patterns, providing their structure reflects perceptual characteristics identified in Tversky and Hemenway's (1984) study of natural objects: Members of the same category had to be perceptually distinctive at the pattern configuration level and perceptually similar at the level of pattern parts. The level of within-category similarity for a set of categories (relative to between-categories similarity) did not predict whether item-specific information would be retained; long-term retention appears to require both within-category similarity and dissimilarity, but at different levels of perceptual structure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Against the likelihood principle in visual form perception.

The likelihood principle, originally formulated by Helmholtz, states that the preferred perceptual organization of a sensory pattern reflects the most likely object or event. This principle of perceptual organization is compared with the minimum principle, which has its origin in the Gestalt tradition. This principle states that we see the simplest possible interpretation of a pattern, given the constraints inherent to the perceptual system. We argue that, as far as perception of visual form is concerned, the likelihood criterion is untenable as a criterion on which the preference for one interpretation over another could be based. Our main argument is that the likelihood principle implicitly starts from interpretations of patterns, whereas it is supposed to explain the existence of those interpretations in the first place. In our view, the likelihood of an interpretation is merely one consequence of the simplicity of the interpretation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual organization of two-dimensional patterns.

The perceptual organization of image patterns is considered from 2 standpoints. First, a theoretical framework is presented from which computational models of perceptual organization can be constructed and tested. Second, a specific computational model for perceptual organization of line images is described. In this model, input images are first processed by a dense array of neurons that have properties consistent with recent analyses of single-neuron responses in primary visual cortex. Then, complex image structure is discovered by interleaved pattern-matching and grouping processes constrained by a generalized uniqueness principle. A series of 3-pattern grouping experiments was performed to test a restricted version of the model and to estimate critical parameters. Using the estimated parameters, an extended version of the model was tested by generating predictions for a series of "textbook" perceptual organization demonstrations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual organization in schizophrenia: The processing of symmetrical configurations.

The hypothesis that the perceptual organization dysfunction of patients with poor premorbid schizophrenia is due to a deficit in global visual sensory store processing was tested by assessing their ability to process symmetrical configurations that develop early and have strong prepotent structures. Two same–different judgment tasks in which performance varies as a function of the symmetrical organization and task demands were administered to participants with good and poor premorbid schizophrenia, those with mood disorders, and normal controls. Like the other groups, poor premorbid schizophrenics' latency and error response patterns closely paralleled the a priori model of adequate processing. The results support their competence in perceptually processing symmetrical configurations and disconfirm the hypothesis that their input deficiencies represent a general deficiency in all forms of perceptual organization. The implications for specifying their early input dysfunction are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Organization of visual short-term memory.

The authors examined the organization of visual short-term memory (VSTM). Using a change-detection task, they reported that VSTM stores relational information between individual items. This relational processing is mediated by the organization of items into spatial configurations. The spatial configuration of visual objects is important for VSTM of spatial locations, colors, and shapes. When color VSTM is compared with location VSTM, spatial configuration plays an integral role because configuration is important for color VSTM, whereas color is not important for location VSTM. The authors also examined the role of attention and found that the formation of configuration is modulated by both top-down and bottom-up attentional factors. In summary, the authors proposed that VSTM stores the relational information of individual visual items on the basis of global spatial configuration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distributed and focused attention: Neuropsychological evidence for separate attentional mechanisms when counting and estimating.

Evidence is presented for 2 modes of attention operating in simultanagnosia. The authors examined visual enumeration in a patient, GK, who has severe impairments in serially scanning across a scene and is unable to count the numbers of items in visual displays. However, GK's ability to judge the relative magnitude of 2 displays was consistently above chance, even when overall luminosity did not vary with the number of items present. In addition, several variables had a differential impact on GK's counting and magnitude estimation. Magnitude estimation but not counting was facilitated by using elements that grouped more easily and by presenting the elements in regular configurations. In contrast, counting was facilitated by placing the elements in different colors while magnitude estimation was disrupted. Also GK's performance on magnitude estimation tasks was disrupted by asking him to count the elements present. The data suggest that GK can process visual stimuli in either a focused or distributed attention mode. When in a focused attention mode, performance is limited by poor serial scanning of attention due to an impaired explicit representation of visual space. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How visual imagery interferes with vision.

Mental visual imagery interferes with vision: the Perky (1910) effect. Is the effect optical, sensory, perceptual, attentional, or just a response bias? Acuity was measured (in undergraduates and graduates) using target lines, with and without images (of lines). Optics (fixation, pupil size, accommodation), response bias, global attention (effort, diversion of attention to imagery), perceptual assimilation (target incorporation by imagery) and perceptual masking (of target by imagery) all fail to explain the effect. Foveally, local attention plays a limited role, as the Perky effect in divided attention is half that in focused attention, but this interaction vanishes with extrafoveal targets. Images produce primarily sensory interference, mimicking a reduction in target energy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of taxonomic organization of named and pictured categories.

Examined 160 3-, 4-, 6-, and 8-yr-old children's preferences for the organization of objects referred to by name only as compared to the organization of depicted objects. On each trial, Ss were shown or told to think about an anchor object and 2 alternative objects, one sharing a perceptual feature and the other from the same superordinate category. Ss were asked which alternative went better with the anchor, and why. After completing the set of triads, Ss were presented with them again and asked whether the unselected alternative could also go with the anchor, and if so, why. For both depicted and named objects, the youngest Ss used and justified both perceptual and taxonomic groupings. With age, Ss came to prefer taxonomic organization and became increasingly aware of both possibilities. The only effect of depiction was to facilitate articulation of perceptual justifications. Thus, it is argued that perceptual organization in young children cannot be attributed to an inability to ignore visual information but seems to be based on the centrality of perceptual features to the representation of objects. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distinguished scientific awards for an early career contribution to psychology: Steven Yantis.

Steven Yantis has explored both stimulus-driven and goal-directed determinants of attention. This work has shown that the sudden appearance of new perceptual objects captures attention in a way that very few other visual events do. It has also revealed how mechanisms of perceptual organization interact with attention to yield efficient dynamic selectivity. This article discusses Yantis's life and contributions to psychology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postattentive vision.

Much research has examined preattentive vision: visual representation prior to the arrival of attention. Most vision research concerns attended visual stimuli; very little research has considered postattentive vision. What is the visual representation of a previously attended object once attention is deployed elsewhere? The authors argue that perceptual effects of attention vanish once attention is redeployed. Experiments 1–6 were visual search studies. In standard search, participants looked for a target item among distractor items. On each trial, a new search display was presented. These tasks were compared to repeated search tasks in which the search display was not changed. On successive trials, participants searched the same display for new targets. Results showed that if search was inefficient when participants searched a display the first time, it was inefficient when the same, unchanging display was searched the second, fifth, or 350th time. Experiments 7 and 8 made a similar point with a curve tracing paradigm. The results have implications for an understanding of scene perception, change detection, and the relationship of vision to memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory dominance in temporal processing: New evidence from synchronization with simultaneous visual and auditory sequences.

Evidence that audition dominates vision in temporal processing has come from perceptual judgment tasks. This study shows that this auditory dominance extends to the largely subconscious processes involved in sensorimotor coordination. Participants tapped their finger in synchrony with auditory and visual sequences containing an event onset shift (EOS), expected to elicit an involuntary phase correction response (PCR), and also tried to detect the EOS. Sequences were presented in unimodal and bimodal conditions, including one in which auditory and visual EOSs of opposite sign coincided. Unimodal results showed greater variability of taps, smaller PCRs, and poorer EOS detection in vision than in audition. In bimodal conditions, variability of taps was similar to that for unimodal auditory sequences, and PCRs depended more on auditory than on visual information, even though attention was always focused on the visual sequences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How do we select perceptions and actions? Human brain imaging studies

The selective nature of human perception and action implies a modulatory interaction between sensorimotor processes and attentional processes. This paper explores the use of functional imaging in humans to explore the mechanisms of perceptual selection and the fate of irrelevant stimuli that are not selected. Experiments with positron emission tomography show that two qualitatively different patterns of modulation of cerebral blood flow can be observed in experiments where non-spatial visual attention and auditory attention are manipulated. These patterns of modulation of cerebral blood flow modulation can be described as gain control and bias signal mechanisms. In visual and auditory cortex, the dominant change in cerebral blood flow associated with attention to either modality is related to a bias signal. The relation of these patterns of modulation to attentional effects that have been observed in single neurons is discussed. The existence of mechanisms for selective perception raises the more general question of whether irrelevant ignored stimuli are nevertheless perceived. Lavie's theory of attention proposes that the degree to which ignored stimuli are processed varies depending on the perceptual load of the current task. Evidence from behavioural and functional magnetic resonance imaging studies of ignored visual motion processing is presented in support of this proposal.     

Attentional control of spatial scale: effects on self-organized motion patterns

Prior to the presentation of a test stimulus, subjects' attentional state was either narrowly focused on a particular location or broadly spread over a large spatial region. In previous studies, it was found that broadly spread attention enhances the sensitivity of relatively large spatial filters (increasing the perceiver's spatial scale), thereby diminishing spatial resolution and enhancing sensitivity to global stimulus structure. In this study it is shown that attentional spread also affects the self-organization of unidirectional versus oscillatory motion patterns for the directionally ambiguous, counterphase presentation of rows of evenly-spaced visual elements (lines segments; dots); i.e. qualitatively different motion patterns can be formed for the same stimulus at different spatial scales. Although the degree to which attention is spread along a spatial axis can be controlled by the perceiver, the effects of spread attention are not limited to a single axis. These results, as well as previously observed effects of attentional spread on spatial resolution, are accounted for by a neural model involving large, foveally-centered receptive fields with co-operatively interacting subunits (probably at the level of MST or higher).     

On the continuity of perceptual experience: Implications for perception and attention.

When an observer views a real-world scene, some objects in the scene are partly occluded by intervening surfaces. Similarly, as the observer moves through the environment, some objects are temporarily occluded and revealed. Yet, although the retinal image is fragmented in space and time, perceptual experience is coherent and continuous. Continuity of experience is achieved by perceptual organization mechanisms, which have their effect before attention. Several experiments are described to illustrate the close interaction between perceptual organization and attention. This interaction determines the representational basis for selection, and is therefore a crucial precursor to understanding object-based mechanisms of visual selection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)