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PubMed2001

Different effects of lorazepam and diazepam on perceptual integration.

Recent research has established the detrimental effect of lorazepam, a benzodiazepine, on both implicit and explicit memory. Furthermore, lorazepam is known to affect perceptual integration. Diazepam, on the other hand, though being a benzodiazepine too, only impairs explicit memory, leaving implicit memory fairly intact. Little is known about the effect of diazepam on perceptual integration. The present study aimed at filling in this gap, by comparing the effects of lorazepam and diazepam on the detection of discontinuities in random-shaped outlines. In line with previous findings, the results in a lorazepam-treated group were quite different from the results in a placebo-treated group. The results in a diazepam-treated group were analogous to the results in the placebo-treated group and different from the results in the lorazepam-treated group. This shows that lorazepam and diazepam differ, not only with respect to their effect on implicit memory, but also with respect to their effect on perceptual integration. It is argued that this bears important consequences for memory research that makes use of a pharmacological dissociation rationale.

Adult↗
PubMed2001

Surface color from boundaries: a new 'watercolor' illusion.

A colored line flanking a darker border will appear to assimilate its color onto the enclosed white area over distances of up to 45 deg (the Watercolor Effect). This coloration is uniform and complete within 100 ms. We found that thin (6 arcmin), winding inducing lines with different contrasts to the ground are generally more effective than thick, straight, and equiluminant lines. Blue and red lines induce the strongest effects, but watercolor spreading may also be seen with green and yellow. On a white background, color spreading is stronger than on chromatic, gray or black backgrounds. Little or no color is perceived when a narrow white zone (gap) is inserted in between the two inducing lines. However, chains of colored dots instead of continuous lines suffice to produce spreading. Edge-induced color is also observed when the two colored lines are presented dichoptically, suggesting a cortical origin. The Watercolor Effect described here may serve to enhance figure-ground segregation by imparting surface color onto the enclosed area, and to promote grouping between distant stimulus elements. As a grouping factor, watercolor coloration wins over proximity. Assimilative color spreading may arise in two steps: First, weakening of the contour by lateral inhibition between differentially activated edge cells (local diffusion); and second, unbarriered flow of color onto the enclosed area (global diffusion).

Color Perception↗
PubMed2001

Two competing mechanisms underlying neon color spreading, visual phantoms and grating induction.

Neon color spreading is closely related to the photopic visual phantom illusion, since these two completion phenomena are characterized by in-phase lightness induction, and the only difference in the stimulus configuration is the difference in the inducer height. This idea was supported by the present study. Neon color spreading showed almost the same function of critical spatial frequency as photopic visual phantoms (Experiment 1), and the critical spatial frequency was constant as the inducer height was changed (Experiment 2). We also examined the relationship between neon color spreading and grating induction (characterized by counterphase lightness induction) in critical spatial frequency (Experiment 3) and in magnitudes of lightness induction (Experiment 4) as a function of the inducer height. The inducer height at which in-phase (neon color spreading) appearance gave way to counterphase (grating) induction was approximately 0.1 deg. These results suggest that neon color spreading shares a common neural mechanism with the photopic visual phantom illusion and that this mechanism is different from, and competes with, the mechanism of grating induction.

Color Perception↗
PubMed2001

Texture fading correlates with stimulus salience.

Perceptual fading of texture targets on similarly textured backgrounds was studied in relation to stimulus salience using texture patterns defined by orientation contrast, shape contrast, and order contrast. In two independent experiments, perceptual salience of the targets was determined. In the first, the textural contrast of the stimuli was varied and their salience quantified using magnitude estimation; in the second, reaction time was measured for the same stimulus patterns. In a third experiment, stimulus fading time was determined. Whereas magnitude estimates and fading time increased, reaction time decreased with increasing textural contrast strength, the shape of the curves depending on the kind of texture pattern used. When fading time was plotted against target salience, the slopes of the regression lines for shape and order contrast were similar, while the slope for orientation contrast was steeper, indicating longer fading times at equal stimulus salience. A control experiment using short oriented bars instead of gratings revealed that this difference may be attributed to the abutting contour between the target and its surround. With this contour removed, the fading time was largely the same for all three kinds of texture patterns. In the absence of a border (no cancellation), the unconnected target areas appeared to change gradually in orientation, shape, and spatial arrangement, thereby assuming the properties of the background (substitution).

Adult↗
PubMed2001

Filling-in of the foveal blue scotoma.

The blue-blindness (tritanopia) of the human foveola normally goes unnoticed but can be directly visualized by having observers view a flickering, monochromatic, short-wavelength field. The blue scotoma appears as a tiny dark spot in central vision, the visibility of which depends upon the wavelength of the field and the temporal frequency of modulation. Comparisons of fading times as a function of flicker frequency for the blue scotoma, foveal afterimages and optically stabilized images indicate a common time course, consistent with the hypothesis that perceptual filling-in of the foveal blue scotoma reflects the operation of neural processes similar to those involved in fading and regeneration of stabilized images.

Afterimage↗
PubMed2002

Contour completion through depth interferes with stereoacuity.

Local disparity signals must interact in visual cortex to represent boundaries and surfaces of three-dimensional (3D) objects. We investigated how disparity signals interact in 3D contours and in 3D surfaces generated from the contours. We compared flat (single disparity) stimuli with curved (multi-disparity) stimuli. We found no consistent differences in sensitivity to contours vs. surfaces; for equivalent amounts of disparity, however, observers were more sensitive to flat stimuli than curved stimuli. Poor depth sensitivity for curved stimuli cannot be explained by the larger range of disparities present in the curved surface, nor by disparity averaging, nor by poor sensitivity to the largest disparity in the stimulus. Surprisingly, sensitivity to surfaces curved in depth was improved by removing portions of the surface and thus removing disparity information. Stimulus configuration had a profound effect on stereo thresholds that cannot be accounted for by disparity-energy models of V1 processing. We suggest that higher-level 3D contour or 3D shape mechanisms are involved.

Form Perception↗
PubMed2003

Children's pursuit eye movements: a developmental study.

We examined the pursuit eye movements of adults and three groups of children 4-6, 8-10, 12-16 years of age. The first experiment compared tracking performance of a partially occluded target with that of a fully visible target. The second experiment examined pursuit abilities of children using a non-cognitive source of information for motion, i.e., proprioception. In this experiment, we compared the ability to track one's own strobe-illuminated finger with the tracking of the experimenter's finger. In the first experiment, only children 4-6 years of age had difficulty inhibiting the tendency to look towards the visible portion of the partially occluded target. They also had significantly fewer epochs of pursuit relative to teenagers and adults. The older children's pursuit eye movements (8-10) were neither significantly different from the youngest nor from the two older groups. In the second experiment, all participants pursued their own finger better than the experimenter's finger, but the youngest children had significantly fewer epochs of pursuit relative to adults. Pursuit of a partially occluded target and incorporation of proprioceptive signals to drive smooth pursuit eye movements are abilities present at four years of age that continue to develop with increasing age.

Adolescent↗
PubMed2003

Filling-in of retinal scotomas.

In this study we examined the perception of one- and two-dimensional patterns across central retinal scotomas, caused by age-related macular degeneration. In contrast with previous studies of disrupted visual input that used the blind spot and artificial scotomas, the current study used large central scotomas caused by physical retinal damage. Such damage is associated with atrophy and long-term cortical reorganization, and it was therefore unclear whether perceptual completion in the damaged system will be similar to that reported for artificial scotomas and the blind spot. In addition, the scotomas under study were much larger and more central than artificial scotomas for which perceptual completion has been reported. For 1-D line and grating patterns, we found perceptual completion across large central scotomas (up to radius of 7 degrees ), which is significantly beyond the range of perceptual completion in artificial scotomas. Gratings completion was better than that of a single line, and increased with bars density. The use of central scotomas allowed us to test the completion of 2-D patterns that are difficult to study in peripheral vision. We found completion of two-dimensional dot arrays over large regions that improved with pattern density and regularity. The results show that in the physically damaged system the range of perceptual completion is increased compared with artificial scotomas, they strongly support the view of an active filling-in process rather than simply ignoring the damaged location, and they show that perceptual completion of physical scotomas is likely to involve cortical processing at multiple levels. We finally discuss implications of the results to the possible use of image enhancement techniques to facilitate the perception of low-vision individuals.

Aged↗
PubMed2003

Visual field anisotropy revealed by perceptual filling-in.

Four experiments were performed to investigate how the time required for perceptual filling-in varies with the position of the target in the visual field. Conventional studies have revealed that filling-in is facilitated by a target with greater eccentricity, while no systematic studies have examined the effect of polar angle. Experiment 1 examined the effect of polar angle when the target and surround differed in luminance. Filling-in was facilitated as the target position changed from the horizontal to the vertical meridian. This dependency was more prominent in the upper field than in the lower, although no asymmetry was found between the left and right visual fields. These features were observed in both monocular and binocular viewing. These results were replicated in a modified stimulus configuration, in which the surround was a circular region concentric with the target (Experiment 2). Moreover, it was confirmed that the asymmetry was not due to fluctuation in the retinal image (i.e., eye movement) (Experiment 3). Finally, Experiment 4 examined whether this anisotropy was observed when two differently oriented gratings were presented in the target and surround regions. Again, filling-in was facilitated for a target close to the vertical meridian, irrespective of the relationship between the target and surround orientations. The underlying mechanism of this anisotropy is discussed from the viewpoints of cortical magnification and neural connections in the visual cortex.

Analysis of Variance↗
PubMed1999

Visual completion of partly occluded grating in infants under 1 month of age.

Four groups of eight infants (3 weeks of age on average) were each habituated to one of four displays consisting of a grating of either low (0.4 cpd) or high (1.2 cpd) spatial frequency, whose central portion was covered up with a horizontal occluder which was either narrow (1.33 degrees) or broad (4.17 degrees). These habituation displays are referred to as LN (low spatial frequency grating and narrow occluder), LB (low and broad), HN (high and narrow), and HB (high and broad) displays. Posthabituation-test displays consisted of a complete grating (CG) of the same frequency as the habituated grating along with a separate grating (SG) whose central portion was replaced with a black gap of the same height as the occluder in the habituation displays. Infants habituated to the LN display looked significantly longer at the SG than the CG display during posthabituation-test trials. Infants habituated to the LB and HN displays looked at the CG and SG displays, almost equally. In contrast, infants habituated to the HB display looked longer at the CG than the SG display. These results show that infants under 1 month of age can perceive the continuation of the grating behind the occluder, and that their visual completion on habituation displays can be evoked according to the interaction between the spatial frequency of the grating and the occluder height.

Evoked Potentials, Visual↗
PubMed1999

The role of convexity in perceptual completion: beyond good continuation.

Since the seminal work of the Gestalt psychologists, there has been great interest in understanding what factors determine the perceptual organization of images. While the Gestaltists demonstrated the significance of grouping cues such as similarity, proximity and good continuation, it has not been well understood whether their catalog of grouping cues is complete--in part due to the paucity of effective methodologies for examining the significance of various grouping cues. We describe a novel, objective method to study perceptual grouping of planar regions separated by an occluder. We demonstrate that the stronger the grouping between two such regions, the harder it will be to resolve their relative stereoscopic depth. We use this new method to call into question many existing theories of perceptual completion (Ullman, S. (1976). Biological Cybernetics, 25, 1-6; Shashua, A., & Ullman, S. (1988). 2nd International Conference on Computer Vision (pp. 321-327); Parent, P., & Zucker, S. (1989). IEEE Transactions on Pattern Analysis and Machine Intelligence, 11, 823-839; Kellman, P. J., & Shipley, T. F. (1991). Cognitive psychology, Liveright, New York; Heitger, R., & von der Heydt, R. (1993). A computational model of neural contour processing, figure-ground segregation and illusory contours. In Internal Conference Computer Vision (pp. 32-40); Mumford, D. (1994). Algebraic geometry and its applications, Springer, New York; Williams, L. R., & Jacobs, D. W. (1997). Neural Computation, 9, 837-858) that are based on Gestalt grouping cues by demonstrating that convexity plays a strong role in perceptual completion. In some cases convexity dominates the effects of the well known Gestalt cue of good continuation. While convexity has been known to play a role in figure/ground segmentation (Rubin, 1927; Kanizsa & Gerbino, 1976), this is the first demonstration of its importance in perceptual completion.

Cues↗
PubMed2006

The visual phantom illusion: A perceptual product of surface completion depending on brightness and contrast.

The visual phantom illusion was first discovered by Rosenbach in 1902 and named 'moving phantoms' by Tynan and Sekuler in 1975 because of its strong dependence on motion. It was later revealed that phantoms can be generated by flickering the grating (flickering phantoms) or by low-luminance stationary gratings under dark adaptation (stationary phantoms). Although phantoms are much more visible at scotopic or mesopic adaptation levels (scotopic phantoms) than at photopic levels, we proposed a new phantom illusion which is fully visible in photopic vision (photopic phantoms). In 2001, we revealed that the visual phantom illusion is a higher-order perceptual construct or a Gestalt, which depends on the mechanism of perceptual transparency. Perceptual transparency is known as a perceptual product based upon brightness and contrast. We furthermore manifested the shared mechanisms between visual phantoms and neon color spreading or between visual phantoms and the Petter effect. In our recent study, the visual phantom illusion can also be seen with a stimulus of contrast-modulated gratings. We assume that this effect also depends on perceptual transparency induced by contrast modulation. Moreover, we found that the Craik-O'Brien-Cornsweet effect and other brightness illusions can generate the visual phantom illusion. In any case, we explain the visual phantom illusion in terms of surface completion, which is given by perceptual transparency.

Contrast Sensitivity↗
PubMed2003

The brain generates its own sentence melody: a Gestalt phenomenon in speech perception.

Brain processes underlying spoken language comprehension comprise auditory encoding, prosodic analysis and linguistic evaluation. Auditory encoding usually activates both hemispheres while language-specific stages are lateralized: analysis of prosodic cues are right-lateralized while linguistic evaluation is left-lateralized. Here, we investigated to what extent the absence of prosodic information influences lateralization. MEG brain-responses indicated that syntactic violations lead to early bi-lateral brain responses for syntax violations. When the pitch of sentences was flattened to diminish prosodic cues, the brain's syntax response was lateralized to the right hemisphere, indicating that the missing pitch was generated automatically by the brain when it was absent. This represents a Gestalt phenomenon, since we perceive more than is actually presented.

Adult↗
PubMed2005

[Adaptation to central scotoma. Part II. Perceptual filling-in phenomenon].

The visual cortex may reorganize after occurrence of a scotoma. Different experimental studies have shown that there is an attempt to minimize the impact of the scotoma, the missing information being filled-in by surrounding information. The clinical consequences of this filling-in phenomenon have been extensively studied by Safran and co-workers. The present review summarizes the current literature on this phenomenon and its clinical consequences. Furthermore, the authors present their own experience with the filling-in phenomenon in patients with age-related macular degeneration. Their study shows that, with few exceptions, the phenomenon only occurs in patients with bilateral central scotoma, in their better eye.

Adaptation, Physiological↗
PubMed2000

Visual cortical mechanisms of perceptual grouping: interacting layers, networks, columns, and maps.

The visual cortex has a laminar organization whose circuits form functional columns in cortical maps. How this laminar architecture supports visual percepts is not well understood. A neural model proposes how the laminar circuits of V1 and V2 generate perceptual groupings that maintain sensitivity to the contrasts and spatial organization of scenic cues. The model can decisively choose which groupings cohere and survive, even while balanced excitatory and inhibitory interactions preserve contrast-sensitive measures of local boundary likelihood or strength. In the model, excitatory inputs from lateral geniculate nucleus (LGN) activate layers 4 and 6 of V1. Layer 6 activates an on-center off-surround network of inputs to layer 4. Together these layer 4 inputs preserve analog sensitivity to LGN input contrasts. Layer 4 cells excite pyramidal cells in layer 2/3, which activate monosynaptic long-range horizontal excitatory connections between layer 2/3 pyramidal cells, and short-range disynaptic inhibitory connections mediated by smooth stellate cells. These interactions support inward perceptual grouping between two or more boundary inducers, but not outward grouping from a single inducer. These boundary signals feed back to layer 4 via the layer 6-to-4 on-center off-surround network. This folded feedback joins cells in different layers into functional columns while selecting winning groupings. Layer 6 in V1 also sends top-down signals to LGN using an on-center off-surround network, which suppresses LGN cells that do not receive feedback, while selecting, enhancing, and synchronizing activity of those that do. The model is used to simulate psychophysical and neurophysiological data about perceptual grouping, including various Gestalt grouping laws.

Animals↗
PubMed2001

Encoding and complex figure recall.

This study investigated the effects of type of encoding strategy (organized and disorganized) and of active versus passive encoding on memory for interrelated spatial material. Delayed recall performance for a complex, nonrepresentational two dimensional figure was measured in 120 normal young adults assigned to one of three groups that varied as to the approach used during the initial construction of the figure. Those applying self-generated strategies performed best. In addition, recall performances were significantly better for those applying a prescribed, organized strategy as compared with performances of those applying a prescribed, disorganized strategy. These effects were not attributable to differences on measures of IQ or spatial information processing. The findings indicated that, independent of memory ability, both the degree of organization and of active strategizing at encoding are determinants of recall ability for complex spatial information and suggest that these factors have implications for memory processes more generally.

Adult↗
PubMed1999

Accentuation and sensitization effects in the categorization of multifaceted stimuli.

Categorization affects perceptions in ways that are assumed to underlie social stereotypes. Research on categorization, however, has focused either on very simple stimuli or on judgmental tasks that focus attention only on single dimensions. To more fully understand the role of categorization in social perception, it is important to examine its effects in the case of multifaceted stimuli and holistic judgments. In 3 studies, participants formed an impression of a focal category of multifaceted stimuli either by itself or in the context of another category. They then judged the typicality of exemplars to the focal category. Results showed that categorization in the presence of a context produced both accentuation and sensitization effects: Participants accentuated between-category differences on relevant dimensions, and they were less sensitive to exemplar differences on irrelevant dimensions.

Adult↗
PubMed1987

Perceptual completion of surfaces in infancy.

Two experiments provide evidence that 4-month-old infants perceive background surfaces as continuous behind occluding objects. Infants were shown a partly hidden background surface either for a brief period of familiarization (Experiment 1) or until they met a criterion of habituation (Experiment 2). The infants were then tested with nonoccluded surfaces that were either continuous or interrupted by a gap where the occluder had been. The infants in each study looked longer at the interrupted than at the continuous surface, relative to infants in baseline controls, which suggests that the partly hidden surface was perceived as continuous. Contrasting findings were obtained in a third experiment, in which infants were habituated to a partly hidden surface that stood in front of a background so that its edges were visible: Infants gave no evidence of perceiving the foreground surface as continuous behind the occluder. These experiments provide evidence that infants perceive a surface as continuous only if it serves as the background of a scene. The results are discussed in relation to figure-ground perception in pictures and surface layouts.

Female↗