PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Form Perception”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,063 records · Page 59Linked to original sources
PubMed1982

Synesthesia. II. Psychophysical relations in the synesthesia of geometrically shaped taste and colored hearing.

The psychophysical function in two synesthetic subjects, one with geometrically shaped taste and the other with colored hearing, is investigated. Each synesthete is compared with three control subjects. Pilot studies are used to construct appropriate response domains. Compared to controls, synesthetes give a restricted set of responses that are also asymmetric with respect to the range of choices available in various subsets of the response domain. A combination of absolute and relative effects is also distinctive of synesthetic percepts. It is concluded that synesthesia is a distinct phenomenon unlike ordinary mediated associations, and occupies an intermediate position in the range of simple to complex brain mechanisms.

Adult↗
PubMed2005

The BOLD response during Stroop task-like inhibition paradigms: Effects of task difficulty and task-relevant modality.

Previous studies of the Stroop task propose two key mediators: the prefrontal and cingulate cortices but hints exist of functional specialization within these regions. This study aimed to examine the effect of task modality upon the prefrontal and cingulate response by examining the response to colour, number, and shape Stroop tasks whilst BOLD fMRI images were acquired on a Siemens 3T MRI scanner. Behavioural analyses indicated facilitation and interference effects and a noticeable effect of task difficulty. Some modular effects of modality were observed in the prefrontal cortex that survived exclusion of task difficulty related activations. No effect of task-relevant information was observed in the anterior cingulate. Future comparisons of the mediation of selective attention need to consider the effects of task context and task difficulty.

Adolescent↗
PubMed2005

Detecting continuity violations in infancy: a new account and new evidence from covering and tube events.

Recent research on infants' responses to occlusion and containment events indicates that, although some violations of the continuity principle are detected at an early age e.g. Aguiar, A., & Baillargeon, R. (1999). 2.5-month-old infants' reasoning about when objects should and should not be occluded. Cognitive Psychology 39, 116-157; Hespos, S. J., & Baillargeon, R. (2001). Knowledge about containment events in very young infants. Cognition 78, 207-245; Luo, Y., & Baillargeon, R. (in press). When the ordinary seems unexpected: Evidence for rule-based reasoning in young infants. Cognition; Wilcox, T., Nadel, L., & Rosser, R. (1996). Location memory in healthy preterm and full-term infants. Infant Behavior & Development 19, 309-323, others are not detected until much later e.g. Baillargeon, R., & DeVos, J. (1991). Object permanence in young infants: Further evidence. Child Development 62, 1227-1246; Hespos, S. J., & Baillargeon, R. (2001). Infants' knowledge about occlusion and containment events: A surprising discrepancy. Psychological Science 12, 140-147; Luo, Y., & Baillargeon, R. (2004). Infants' reasoning about events involving transparent occluders and containers. Manuscript in preparation; Wilcox, T. (1999). Object individuation: Infants' use of shape, size, pattern, and color. Cognition 72, 125-166. The present research focused on events involving covers or tubes, and brought to light additional examples of early and late successes in infants' ability to detect continuity violations. In Experiment 1, 2.5- to 3-month-old infants were surprised (1) when a cover was lowered over an object, slid to the right, and lifted to reveal no object; and (2) when a cover was lowered over an object, slid behind the left half of a screen, lifted above the screen, moved to the right, lowered behind the right half of the screen, slid past the screen, and finally lifted to reveal the object. In Experiments 2 and 3, 9- and 11-month-old infants were not surprised when a short cover was lowered over a tall object until it became fully hidden; only 12-month-old infants detected this violation. Finally, in Experiment 4, 9-, 12-, and 13-month-old infants were not surprised when a tall object was lowered inside a short tube until it became fully hidden; only 14-month-old infants detected this violation. A new account of infants' physical reasoning attempts to make sense of all of these results. New research directions suggested by the account are also discussed.

Cognition↗
PubMed2004

Perceptual biases in the interpretation of 3D shape from shading.

Two experiments are reported in which observers judged the sign and magnitude of surface curvature from shaded images of an indoor scene. The depicted surfaces were illuminated by an area light in the ceiling or floor, and the illumination was attenuated with distance in a physically correct manner. The displays were presented both with and without cast shadows, specular highlights and surface inter-reflections in all possible combinations. The overall pattern of results revealed a strong perceptual bias to interpret the images as convex rather than concave, and a weaker bias to prefer illumination from above rather than from below, though there were large individual differences in the relative strengths of these biases. For displays that did not contain cast shadows or specular highlights, the accuracy of observers' judgments about the sign of surface curvature was no greater than chance, but performance was significantly improved when those aspects of normal shading were included in the rendering model. An analysis of the apparent depth magnitudes revealed that convex surfaces produce much greater perceived depth than concave surfaces with comparable relief.

Depth Perception↗
PubMed2004

Attentional effects on sensory tuning for single-feature detection and double-feature conjunction.

When humans scan their visual environment, relevant objects are selectively attended for enhanced processing. It is still unclear in what ways processing is modified by attention, and whether attentional selection operates on an individual feature (such as colour, orientation or motion) or on binding together different features. In the experiments reported in this paper, these two stages were characterized using psychophysical reverse correlation. Subjects viewed eight patches, briefly flashed and symmetrically arranged around fixation. Each patch consisted of segments that could vary in both colour and orientation. One of the patches ('target') differed from the remaining 'distractor' patches with respect to either its orientation, colour, or both (in three different experiments). Subjects were asked to detect the target patch. The stimulus was preceded by a cue. On some trials ('cued' trials), the cue informed observers that the target patch could only appear at two of the eight possible locations. On remaining ('uncued') trials, all eight positions were valid. Psychophysical reverse correlation was then applied to derive linear estimates of sensory filters for orientation only, colour only, and their conjunction. In line with the properties of single neurons in cortex, attentional cueing did not affect sensory tuning for detecting individual features. However, it affected the way in which features were subsequently (and very inefficiently) combined in a multiplicative fashion. The results are consistent with a model in which attention recalibrates internal responses to the statistics of the stimulus by having signals from different features mutually control each other through reciprocal inhibition.

Attention↗
PubMed2005

The interaction of shape- and location-based priming in object categorisation: evidence for a hybrid "what + where" representation stage.

The relationship between part shape and location is not well elucidated in current theories of object recognition. Here we investigated the role of shape and location of object parts on recognition, using a classification priming paradigm with novel 3D objects. In Experiment 1, the relative displacement of two parts comprising the prime gradually reduced the priming effect. In Experiment 2, presenting single-part primes in locations progressively different from those in the composite target had no effect on priming. In Experiment 3, manipulating the relative position of composite prime and target strongly affected priming. Finally, in Experiment 4 the relative displacement of single-part primes and composite targets did influence response time. Together, these findings are best interpreted in terms of a hybrid theory, according to which conjunctions of shape and location are explicitly represented at some stage of visual object processing.

Adolescent↗
PubMed1997

Color processing in object verification.

This study examined the effect of different object verification tasks on perceptual and conceptual color processing. Participants decided whether two successively presented stimuli (two pictures or a word then a picture) referred to the same object. Although the task did not require object-color processing, prototypical object-color was semantically activated and influenced verification decisions. This automatic conceptual color processing was more powerful than perceptual processing of the surface color presented in the picture. Moreover, conceptual color processing occurred in tasks involving only two pictures, implying that activation of prototypical color does not depend on verbal processing. Rather, activation of prototypical color depends on whether pictures are semantically encoded during verification, which in turn, occurs when verification cannot proceed from structural object information.

Cognition↗
PubMed1978

The effects of cuing on picture naming in aphasia.

This study compared the facilitative values of six types of cue for eliciting picture naming responses from Brocas, Wernickes, and anomic aphasics. Degree of responsivity to cues was inversely related to severity of naming disorder. Type of cue, severity of naming disorder, and diagnostic category contributed significantly to the results obtained, though the diagnostic groups did not show differential patterns of response to the cues. First Sounds and Completion sentences were the most effective cues. The finding of diagnostic group differences in degree of responsivity to cues, without differential sensitivity to type of cue, was interpreted as indicating that a single factor might account for group differences in ability to benefit from cuing.

Aphasia↗
PubMed1996

Congenital visual agnosia and prosopagnosia in a child: a case report.

We present an eight years old child, L.G. with congenital agnosia and prosopagnosia. This is a special case of perceptual deficits in a child which are discrete and exist in the context of a very high verbal intelligence. L.G. was administered an extensive battery of tests of cognitive functioning. He has intact basic visual skills, although his visual analysis is sometimes slow. L.G. can read, write and do math at age level or above. Four normal eight years old boys were used as controls on a selection of the perceptual tests, administered to L.G., which did not have normative data. L.G.'s object recognition skills bear the hallmarks of adult apperceptive agnosia. His visual memory and imagery are normal. Tests of face processing skills reveal, unlike adult prosopagnosics, severe deficits in addition to the familiar face recognition problem. L.G.'s agnosia and prosopagnosia are compared to the relevant literature.

Agnosia↗
PubMed2000

What limits the contribution of second-order motion to the perception of surface shape?

Both motion and stereopsis can be derived from contrast as well as luminance defined stimuli. It is currently assumed that these two different sources of information about objects feed into one common stage. Thus it would not be expected that their role in visual perception would be different. Here we show that although motion can be carried by contrast-defined elements, such motion is not used to define three-dimensional (3D) surfaces. A similar effect has been reported in stereopsis; although such contrast-defined elements can give signed disparity signals they nevertheless do not contribute to the percept of shape. We show that the reason for this lies in the inability of the second order signals to cohere or bind across space/spatial scales rather than a characteristic of the elementary motion signals per se.

Contrast Sensitivity↗
PubMed2000

Surface integration influences depth discrimination.

Image fragments arising from partial occlusion may be perceptually unified by a surface integration process on the basis of similar color or texture. In a new objective measure pitting surface feature similarity against binocular disparity, observers discriminated whether a colored circle had either crossed or uncrossed disparity relative to a surrounding gray rectangle. Sensitivity to disparity was impaired only when (1) the configuration of the other surface fragments in the display supported the integration of a surface behind the rectangle and circle, and (2) matched the color of the central circle. Results were consistent with the hypothesis that a surface integration process integrated similarly-colored surface fragments into a smooth surface, even when those fragments were at different depths. Surface integration caused small and reliable effects on depth perception despite unambiguous disparity information. Perceived depth does not depend solely upon disparity, and may be determined after three-dimensional figural unity is established.

Color Perception↗
PubMed2001

Size-based selection in rapid serial visual presentation.

Several recent studies [Farell, B., & Pelli, D. (1993). Can we attend to large and small at the same time? Vision Research, 33, 2757-72; Shih, S., & Sperling, G. (1996). Is there feature-based attentional selection in visual search? Journal of Experimental Psychology: Human Perception and Performance, 22, 758-79] have found that visual selection based on the size of stimuli is impossible when the stimuli are presented in rapid succession in overlapping positions (RSVP paradigm). In the present study effective size-based selection is demonstrated in several conditions with RSVP stimuli. Attention to specific size is highly efficient when stimuli are presented in a single location (at fixation point) and may be possible also with a few (2-4) locations. When overlapping small and large characters are presented without abrupt onsets, then selection by size is effective at least over six locations. The results are explained by certain mandatory properties of spatial attention.

Adult↗
PubMed2003

Effects of pictorially-defined surfaces on visual search.

Three experiments of visual search for a cube (for a square pillar in Experiment 3) with an odd conjunction of orientation of faces and color (a cube with a red top face and a green right face among cubes with a green top face and a red right face, for example) showed that the search is made more efficient by arranging cubes (or square pillars) so that their top faces lie in a horizontal surface defined by pictorial cues. This effect shows the same asymmetry as that of the surface defined by the disparity cue did [Perception and Psychophysics, 62 (2000) 540], implying that the effect is independent of the three-dimensional cue and the global surface structure influences the control of attention during the search.

Adult↗
PubMed1999

An orientation anisotropy in the effects of scaling vertical disparities.

Gårding et al. (Vis Res 1995;35:703-722) proposed a two-stage theory of stereopsis. The first uses horizontal disparities for relief computations after they have been subjected to a process called disparity correction that utilises vertical disparities. The second stage, termed disparity normalisation, is concerned with computing metric representations from the output of stage one. It uses vertical disparities to a much lesser extent, if at all, for small field stimuli. We report two psychophysical experiments that tested whether human vision implements this two-stage theory. They tested the prediction that scaling vertical disparities to simulate different viewing distances to the fixation point should affect the perceived amplitudes of vertically but not horizontally oriented ridges. The first used elliptical half-cylinders and the 'apparently circular cylinder' judgement task of Johnston (Vis Res 1991;31:1351-1360). The second experiment used parabolic ridges and the amplitude judgement task of Buckley and Frisby (Vis Res 1993;33:919-934). Both studies broadly confirmed the anisotropy prediction by finding that large scalings of vertical disparities simulating near distances had a strong effect on the perceived amplitudes of the vertically oriented stimuli but little effect on the horizontal ones. When distances > 25 cm were simulated there were no significant differential effects and various methodological reasons are offered for this departure from expectations.

Adult↗
PubMed1999

Measuring perceived 3D shape at multiple spatial scales.

We present and test a novel multiscale representation of perceived 3D surface orientation: the orientation path. Using a multiscale probe, we measure perceived surface orientation at multiple spatial scales; linking the measurements for a given surface location yields that location's orientation path. The multiscale data obtained show that observers consistently see different surface orientations at different spatial scales. We demonstrate that such multiscale data can reveal multiscale differences between observers' percepts of a stimulus and the stimulus geometry. We also demonstrate the use of the orientation path in evaluating the multiscale effects of adding a depth cue to a 3D display.

Computer Graphics↗
PubMed2000

Global factors that determine the maximum disparity for seeing cyclopean surface shape.

A disparity gradient limit explains why the maximum amplitude of sinusoidal disparity gratings increases with decreasing disparity spatial frequency. It also explains why the largest disparity for binocular fusion (diplopia threshold) varies directly with stimulus element separation. Does a disparity gradient limit also apply to the detection of cyclopean shape? A previous study addressed this question and concluded that it does not. We examined this question by measuring the largest disparity amplitude (dmax) at which observers could judge the shape of cyclopean disparity gratings. We used trapezoidal, triangular, sinusoidal, and square wave gratings in order to dissociate the effects of disparity gradient and disparity spatial frequency. Gabor micropatterns were used to minimize potential scale-dependent interactions with luminance processing. Our results support a disparity gradient limit for cyclopean shape perception, with additional factors being involved at high disparity spatial frequencies. Combining the gradient limit hypothesis with lowpass disparity filtering describes the pattern of dmax for both smooth and discontinuous surface shapes.

Depth Perception↗
PubMed2001

Irrelevant digits affect feature-based attention depending on the overlap of neural circuits.

Feature-based attention was investigated by examining the effect of irrelevant information on the processing of relevant information. In all experiments, irrelevant information consisted of digits whose semantic information is known to be processed in parietal areas. Between experiments we varied the degree of parietal involvement in the processing of the relevant feature. The influence of the irrelevant digit on the binary manual response task on the relevant feature was measured by the SNARC effect, a spatial numerical association of response codes demonstrating faster left than right hand responses for small numbers and faster right than left hand responses for large numbers. When processing of the relevant feature depended on parietal cortex, as is the case for orientation processing (exps. 1 and 4), there was an effect of the digit's semantic value on response times. Conversely, there was no effect of the irrelevant digit on the processing of color (exps. 2 and 3) or shape (exp. 5), which rely only minimally on parietal resources. After ruling out alternative explanations we conclude that the efficiency of feature-based attention is determined by the degree of neural overlap of structures dedicated to process relevant and irrelevant information.

Adult↗