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PubMed1991

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↗
PubMed1992

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↗
PubMed1975

[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↗
PubMed1992

[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↗
PubMed1992

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↗
PubMed1991

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↗
PubMed1989

Mental representation and hypothetico-deductive reasoning: the case of the THOG problem.

This article reports three experiments that deal with the source of the difficulty of Wason's (1977) THOG problem. The solution of this problem demands both the postulation of hypotheses and a combinatorial analysis of their consequences. Experiment 1 showed that the generation of the hypotheses is not in itself sufficient to solve the problem. Experiment 2 showed that a version presenting a plausible context for separating the level of data from that of hypotheses produced a better performance than both the original abstract version and a thematic version lacking the plausible context separating the levels. Experiment 3 gave evidence that this context can produce facilitation even with the geometric material of the classic version. This experiment also showed that a pictorial presentation of data and a verbal presentation of hypotheses affect performance negatively. The results demonstrate the role of problem representation in problem solving, and, in particular, the role of homogeneity in representing data and hypotheses in hypothetico-deductive reasoning.

Adult↗
PubMed1992

Prehension movements directed to approaching objects: influence of stimulus velocity on the transport and the grasp components.

In this investigation we studied the influence of object velocity on the transport and on the grasp components of prehension movements directed to approaching objects. Three experiments were carried out. In the first experiment six subjects were required to reach and grasp a sphere that approached them with a constant velocity. The effects of four velocities were studied. The results showed that the end point of the arm movement changed with object velocity: nearer the body with higher than with lower object velocities. Transport velocity increased with movement amplitude and the deceleration phase decreased in duration with higher object velocities. On the contrary the grasp component was not affected by object velocity. The second experiment was a control experiment carried out in order to verify whether a possible influence of object velocity on the grasp could be revealed in an experimental condition in which grasp planning relies without doubt on visual computation of all object features. In this experiment object velocity and object size were randomly varied. The results showed that the grasp was not influenced by object velocity, whereas it was sensitive to changes of object size. The third experiment had the two-fold aim of establishing (1) whether transport velocity was influenced by object velocity once the location in space at which the object had to be grasped was fixed and (2) whether the grasp kinematics differed for prehension movements directed respectively to stationary or to moving objects. Results showed that the first part of the transport is affected only by distance, whereas the deceleration phase decreased with increasing object velocity. This last result suggests that subjects minimized object displacements in order to grasp the sphere correctly. The grasp component differed between the conditions of stationary and moving stimuli only in the relative timing between finger aperture and closure phases. The closure phase decreased in the condition of moving stimuli. The results of the three experiments indicate the dependence of transport parameters on object velocity, whereas grasp parameters appear to be unaffected.

Acceleration↗