Color, light, and the perception of form.
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Results for “Form Perception”
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[Dynamics of the amplitude change in the acoustic reflex of the stapedius muscle in various forms of perceptive hypoacusis].
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Acoustic Impedance Tests↗
[The significance of the CNS for the physiology of hearing (author's transl)].
Some general aspects of auditory perception (funnelling, contrast, pattern recognition, form perception, methodological limitations) are discussed in the first part of this presentation. The modern concept of the hydrodynamics of the inner ear, including electronic modelling of the function of the basilar membrane is their dealth with. For the encoding and decoding processes of the auditory system the different grades of intensity function at the different neuronal levels is compared with that of the envelope of the basilar membranes deflection. The influence of the efferent system is discussed. In a third section of the paper some new results from our department are reported concerning the single unit activity at geniculate level recorded from the awake cat by means of a telemetric system. Neurophysiological correlates to vowel- and consonant detectors and their relations to be the phonem recognition of speech could be demonstrated. Finally, the most recent state of objective audiometry is discussed (DC-potentials, simultaneous records of electrocochleogram and cortically evoked activity, relations to EEG's power spectrum, and brains changes in vigilance) with a view of future approaches to ERA.
Animals↗
Defective processing of motion-defined form in the fellow eye of patients with unilateral amblyopia.
The following three measurements were made on a group of 20 pediatric and 5 adult patients with unilateral amblyopia: (1) speed threshold for recognizing motion-defined dotted letters; (2) recognition acuity for isolated solid letters of 4% contrast; and (3) Snellen line acuity for high-contrast letters. Normal limits were established with a group of 30 pediatric and 10 adult control subjects. The main finding was that, in amblyopic children, a high percentage (83%, 15 of 18) of fellow eyes showed a degraded ability to recognize motion-defined letters, even though Snellen acuity and 4% letter acuity were normal for age. The fellow eyes of all nine patients with strabismic amblyopia showed this pattern of loss, as did four of six fellow eyes of patients with anisometropic amblyopia and two of three fellow eyes of patients with anisometropic plus strabismic amblyopia. Only two clinically unaffected eyes were normal for motion-defined letters. These eyes belonged to patients with anisometropic amblyopia. Eighteen of the 19 previously amblyopic eyes tested were abnormal for motion-defined letters even though Snellen acuity was within normal limits for 6 of these eyes. In adults, only one of five fellow eyes failed the motion-defined letter test. It was concluded that the degradation of form perception associated with amblyopia can be different for luminance-defined and motion-defined form and that defective processing of motion-defined form is common in the fellow eyes of children with unilateral amblyopia.
Adolescent↗
Global detection of symmetry.
Two experimental approaches examined observers' ability to characterize shape symmetry based upon the information obtained within a single fixation. Exp. I tested observers' ability to discriminate among three levels of symmetry on the basis of a 25-msec. presentation. Results indicated that identification accuracy was higher for symmetrical and asymmetrical shapes than for mixed shapes, which contained both symmetrical and asymmetrical components. Exp. II tested observers' ability to detect a given level of symmetry by means of a signal-detection approach. Symmetrical shapes were detected better than asymmetrical shapes. Detectability of mixed shapes was lower than that for both symmetrical and asymmetrical shapes. The results of Exps. I and II demonstrate that observers can characterize shape symmetry on the basis of information available within a single fixation. The data are supportive of the hypothesis that a global response to the over-all configuration of the shape serves to facilitate form perception.
Discrimination, Psychological↗
Pictorial and motion-based information for depth perception.
When computer-generated objects approached the viewpoint in midair, a large far object appeared to be nearer than a small near object and appeared to hit the viewpoint before the small object, which was specified by time-to-contact information to arrive sooner. These judgements were consistent with relative size and occurred even when motion-based information was potentially above threshold. The effects of relative size persisted with higher resolution animated films of approaching objects, were weakened by ground-intercept information, and were not as robust with laterally translating objects. Although it is often asserted that the kinds of information that have traditionally been called static depth cues are superseded by motion-based depth information, this article attempts to show that the reverse also can occur in distance perception, as has been shown in form perception.
Adult↗
Newborn infant attention to form of contour.
Human neonates selectively fixated patterns with curved rather than straight contours when the outermost contours differed in this form variable and when quantitative variables were controlled. The presence from birth of a discrimination ability basic to later form perception was evidenced.
Attention↗
Visual acuity functions and pattern discrimination in the destriate cat.
The study provides evidence that the cat is capable of processing visual information of some detail after removal of area 17 and most of area 18. This postoperative discrimination of complex spatial stimuli is not based on the use of such cues as luminance differences or local flux cues. From the deficits which follow extensive lesions of areas 17-18, it appears as though these cortices participate in the detection of fine details. We found a modest increase in the threshold of grating acuity, moderate loss in orientation acuity and extensive deficit in a task requiring topographic alignment of contours (vernier offset). Further evidence for the substantial preservation of spatial vision in the destriate cat is provided by experiments which show that perceptual grouping of rectilinear arrays of figural elements (dots or line segments) into obliquely oriented rows is largely unaffected by the lesion, even when the grouping is initiated by near-threshold proximity cues. Since grouping effects are felt to be involved in the organization of the visual field into the figure-ground dichotomy, these results indicate that the neural mechanisms subserving the initial stage of form perception lie outside of areas 17 and 18. Consistent with the increased acuity thresholds of destriate cats, these animals have deficits in several pattern discriminations that require fine-grained spatial analysis The results suggest that areas 17-18 serve as a high-spatial frequency analyzer, but are not essential to pattern and form recognition.
Animals↗
The computation of perceptual structure from collinearity and closure: normality and pathology.
Three experiments tested how structural information affects the processing of fragmented forms, using evidence from both normal subjects and an agnosic patient. The stimuli were either (a) outline drawings of objects; (b) "well" or "poorly" structured fragmented forms derived from outline drawings (Experiments 1 and 2) or (c) "well" or "poorly" structured fragmented forms derived from outline drawings of meaningless forms (Experiment 3). "Well" and "poorly" structured forms varied on the properties of collinearity and closure of the elements. Subjects decided if two simultaneously presented forms had the same orientation or were mirror-reversed. Three levels of discriminability were examined: (a) for "symmetrical" forms the decision had to be based on the detection of a small feature appearing on the same or the opposite side in the two forms; (b) for "asymmetrical" forms the decision had to be based on a large part located on the same or the opposite side of each object; and (c) for "oblique" forms, matching could be based on the global orientation of the shapes. Normal subjects performed equivalently on outline drawings and "well" structured fragmented forms and worse on "poorly" structured forms. This effect was strongest on "asymmetrical" stimuli, both with meaningful (Experiments 1 and 2) and meaningless forms (Experiment 3). This indicates that the segmentation of forms into parts, for judgements with "asymmetrical" stimuli, is affected by the structural properties of collinearity and closure. For the agnosic patient, performance was similar for "well" and "poorly" structured forms, and there was better performance in the "oblique" condition. This suggests that the patient could use global shape information, but that this coexists with a selective deficit in computing local perceptual structure, based on collinearity and closure between form elements. The implications of the results for understanding form perception and the clinical use of fragmented forms, are discussed.
Adult↗
Irrelevance of figural identity for resolving ambiguities in apparent motion.
In order to examine the degree to which form perception affects the formation of apparent-motion experience, subjects were presented with nine ambiguous apparent-motion situations, where the elements of each single flash were various figures. One of the interpretations of each situation preserved the figural identity of the figures across flashes. It was found that figural identity does not have any effect on determining the type of motion experienced, except when the figural analysis involved is relatively simple.
Form Perception↗
Sensory integrative processing in delinquent-prone and non-delinquent-prone adolescents.
The purposes of this study were to obtain a preliminary description of the sensory integrative and practic abilities of 114 non-delinquent-prone adolescents aged 12 through 18 years and to compare their performances with those of 12 delinquent-prone adolescents with learning problems. Ten of the 17 subtests of the Sensory Integration and Praxis Tests (SIPT) (Ayres, 1989) as well as the Finger Posture Imitation Test (Druker, 1980) and the MacQuarrie Test for Mechanical Ability (MacQuarrie, 1925/1953) were administered to both groups. It was hypothesized that performance on some tests would correlate with age in the non-delinquent-prone adolescents. It was also hypothesized that some delinquent-prone adolescents with learning problems would perform significantly worse on the tests of sensory integrative and practic abilities than would the non-delinquent-prone adolescents. A data analysis indicated that performance on the praxis tests, Manual Form Perception, Graphesthesia, and Bilateral Motor Coordination showed a significant age correlation. The results of this study indicated a difference between the two groups, and it was concluded that the delinquent-prone group performed more poorly on all of the praxis-related tests and on the absolute values of the tests of Postrotary Nystagmus, Standing and Walking Balance, and Bilateral Motor Coordination. Some of the vestibular- and praxis-related tests, therefore, may still provide useful information on children older than 8 years of age.
Adolescent↗
Image enhancement for the visually impaired. Simulations and experimental results.
Digital image enhancement has been proposed as an aid for the visually impaired. The capability of two enhancement techniques to improve recognition of images by patients with central scotoma or cataracts was evaluated using image-processing simulations and direct patient testing. Enhancements and simulations were based on measurements of contrast sensitivity loss for patients with macular disease. Contrast sensitivity loss was measured using Gabor-type localized stimuli and paradigms that are appropriate for analyzing form perception. The simulations using the contrast sensitivity data suggested that patients with moderate visual loss (20/70-20/200) may have difficulty recognizing faces and may benefit from enhancement by both of the techniques used. Ability to recognize celebrities from enhanced images improved for 39 of the 46 patients tested. The improvement was significant (P less than 0.05) for 16 of the 38 patients with central visual loss and for 3 of 8 patients with anterior segment media opacities tested. The simulations suggest that the benefits of image enhancement may be similar or even greater for recognition of other types of images.
Adult↗
Neural mechanisms of tactual form and texture perception.
In the last decade or so, there has been rapid movement toward the use of more complex stimuli in the study of perceptual function related to the hand. This review has focused on the neural mechanisms of form and texture perception. Evidence from neurophysiological and psychophysical studies in which static touch, scanning touch, and the Optacon were used indicate that the spatial acuity of the RA system may be as much as three times poorer than the SAI system, evidence that suggests that form perception is dominated by the SAI system. Pattern recognition behavior in a tactual letter recognition task appears to be directly related to the response properties of SAI afferent fibers. Psychophysical studies of roughness perception show that roughness magnitude is related to surface structure in an orderly manner. Because roughness varies along an intensive continuum, mean impulse rate in one or more of the afferent systems is the most obvious coding possibility. No satisfactory relationship between mean impulse rate and roughness has been observed, however. The strongest hypothesis is that tactual roughness perception is based on spatial variation in the SAI population response. The combined evidence from studies reviewed here suggests complementary roles for each of the afferent systems, which are presented as working hypotheses: The SAI system is the primary spatial system and is responsible for tactual form and roughness perception when the fingers contact a surface directly and for the perception of external events through the distribution of forces across the skin surface. The PC system is responsible for the perception of external events that are manifested through transmitted high-frequency vibrations of the kind that are critical in the use of objects as tools. The RA system is responsible for the detection and representation of localized movement between skin and a surface as well as for surface form and texture when surface variation is too small to activate the SAI afferents effectively.
Animals↗
[Functional hemispheric asymmetry in perception of random forms (author's transl)].
2 experiments were conducted in which Ss made the "same-different" judgement with respect to a pair of random forms which were serially presented to the right and the left VF tachistoscopically. In Exp. I, the stimulus materials were random form painted solidly, and in Exp. II they were contour forms. The major results of both experiments were essentially the same. The results indicated that right VF-lead condition produced more errors than the left VF-lead condition, and that the high complexity form group produced more errors than the low complexity form group. The tendency of left VF-lead superiority was more pronounced when the interval between the 2 stimuli was longer. These results suggest the possibility of the right hemisphere's superior function concerning the perception of random forms.
Adult↗
[Practical games--one of the forms of independent student work].
The games imitating a clinical pathology conference and a session of the therapeutical-control commission are an efficient method of student learning during the biopsy-sectional course. They favour activation of perception, form clinico-anatomical thinking, facilitate the learning of the diagnosis concept and the role of physicians of various profile (therapeutist, surgeon, pathologist, gynecologist, etc.).
Education, Medical↗
Information compression in dynamic radiological studies.
The large volumes of digital image data from radiological examinations demand further research and practical solutions in image compression before PACS solutions in large radiological departments are plausible. But another type of compression of image information is also possible, which has, in fact, been somewhat utilized already in analog form, but which has far better possibilities in the digital world. The number of essential images in dynamic X-ray, nuclear medicine, examinations etc. can be greatly reduced. These examinations producing image series are reviewed in terms of compression of information. 3-D displays are very useful in slice imaging, because they provide a means to see easier inside the human body than a number of slice images side by side. We also provide a new method, dynamic pulmonary imaging with digital fluoroscopy, as an example of the digital possibilities to compress a number of images into parametric images, numbers, histograms and curves. These processes also have other positive consequences information is transformed into a more easily perceptible form.
Diagnostic Imaging↗
Orientation discrimination in the cat: its cortical locus. I. Areas 17 and 18.
An elementary unit of visual pattern and form perception is thought to be the orientation of edges; this element has been studied extensively by neurophysiologists using oriented line segments or bars. These same stimuli have been used in the present study to measure threshold discriminations in cats before and after cortical lesions of areas 17 and/or 18. Control experiments showed that the discriminations were made by using a single cue, orientation, and that other stimulus parameters, width, length and contrast of the bar, were optimized. The extent of the lesions was evaluated anatomically from cell and fiber stained sections through cortex and thalamus, matched to retinotopic maps of Tusa et al. (Cortical Sensory Organization, Vol. 2, Humana Press, pp. 1-31, '81) and Sanderson (Journal of Comparative Neurology 143:101-118, '71), and physiologically from visual field position of receptive fields of cells recorded in areas neighboring the lesions. Lesions involving area 17 and large parts of area 18 produced a marked deficit in orientation discrimination which included a loss in retention, and after retraining a substantial increase in thresholds for up to 3 years when tested with long bars. There was no recovery of discrimination when the animals were tested with short bars. Lesions which involved area 17 plus small parts of 18, or lesions of areas 18 and 19, produced no retention deficit and resulted in an increase in thresholds only at low contrast and narrow width. These experiments revealed an excellent correlation between lesion locus and size and behavioral deficit. They indicate that the cortical representation of bar orientation used for discrimination is distributed within and across areas 17 and 18. The spread of the distribution depends on other stimulus parameters such as bar width and length. Furthermore the experiments show that neither the most narrowly tuned cells nor the X-cell system is required for fine orientation discrimination of a long bar.
Animals↗
A vector model for perceived object rotation and translation in space.
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Depth Perception↗