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PubMed1977

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↗
PubMed1987

Dichaptic-visual form matching in adults.

Although previous visuo-dichaptic matching studies report hemispheric asymmetries in spatial-form perception, more recent studies have failed to support these findings. Three cross-modal matching experiments examined hemispheric asymmetries in adult spatial-form matching. In the first experiment, subjects simultaneously felt two eight-point or 12-point tactile shapes patterned after Vanderplas and Garvin (1959) for four seconds and were then required to identify both shapes from a visual response array. Results showed subjects were significantly better identifying eight point shapes. A marginally significant feeling hand by pointing hand interaction indicated that recognition accuracy was higher when shape ipsilateral to the pointing hand was identified. In the second experiment, only one of the two tactile shapes had to be identified from the visual array. Results showed a significant interaction between complexity and feeling hand, where the left and right feeling hands were respectively better at identifying 12-point and eight-point shapes. The third experiment was an attempt to more directly examine the Witelson (1976) experiment using her spatial-form stimuli. Results showed no significant laterality nor stimulus-response compatibility effects. These findings are discussed in terms of cerebral asymmetry and stimulus-response compatibility models.

Adult↗
PubMed1986

Cortical mechanisms for local and global analysis of visual space in the cat.

The effects of lesions in the striate or extra-striate visual cortex of cats were evaluated using visual discrimination problems which required either local or global pattern processing. The results indicate that damage to areas 17 and 18 preferentially impairs local processes, while in addition they suggest that damage to the extra-striate cortex preferentially affects global processing. These findings may be related to the observations that cats with large lesions in the extra-striate cortex demonstrate deficits in form perception without reductions in visual acuity and those with lesions in areas 17-18 show elevations of acuity thresholds while maintaining excellent pattern and form vision.

Animals↗
PubMed1991

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↗
PubMed1982

Influence of vision on haptic encoding processes.

Sighted subjects (n = 15) assembled 6-piece jigsaw puzzles under four conditions of visual-haptic perception which both separated these perceptual systems and required the simultaneous use of vision and touch. The time required and haptic scanning strategies used to assemble the puzzles in each of the four conditions were examined to determine the influence of type of visual involvement upon haptic encoding processes and the degree to which the visual and haptic systems are linked. Results indicate that a cognitive component is involved during visual-tactual form perception which affects how the perceptual modalities work together and how information is selected, encoded, and processed. When vision and touch were used simultaneously to examine the same stimulus, and visual information was adequate for responding, vision dominated touch. However, in conditions of visual-haptic perception in which visual input was inadequate for responding or when haptic perception was independent of vision, subjects relied upon a form of information which was specifically tactual in nature and independent of visual or verbal recoding.

Discrimination Learning↗
PubMed1975

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↗
PubMed1983

Global and local precedence: selective attention in form and motion perception.

This study explores the perception of stimuli at two levels: local parts and the wholes that comprise these parts. Previous research has produced contradictory results. Some studies (e.g., Pomerantz & Sager, 1975) show local precedence, in which the local parts are more difficult to ignore in selective attention tasks. Other studies (e.g., Navon, 1977) have shown the opposite effect, global precedence. The present five experiments trace the causes of this discrepancy by exploring the effects of the relative discriminabilities of the local and global levels of the stimuli and the differences between two different measures of selective attention, namely, Stroop-type interference (attributable to incongruity on the irrelevant dimension) and Garner-type interference (attributable to variability on the irrelevant dimension). The experiments also examine whether the precedence effects previously examined in form perception generalize to motion perception. The results show that (a) some cases of global precedence are due solely to the greater perceptual discriminability of the global level and thus demonstrate only that more discriminable stimuli are harder to ignore; (b) instances of both local and global precedence can be demonstrated for certain types of stimuli, even when the discriminabilities of their local and global levels have been equated; and (c) the Stroop and Garner measures of selective attention are not equivalent but instead measure different types of interference. In addition, a distinction is made between two fundamentally different types of part-whole relationships that exist in visual configurations, one based only on the positions of the parts (Type P) and one based also on the nature of the parts (Type N). Previous research has focused on Type P, which appears to be irrelevant to the broader questions of Gestalt and top-down effects in perception. It is concluded that bona fide cases of both local and global precedence have been amply documented but that no general theory can account for why or when these effects will appear until we better understand both the nature of part-whole relationships and the perceptual processes that are tapped by different measures of selective attention.

Adult↗
PubMed1984

Perturbing line pictures for identification of visual features and their syntax.

Experiments are reported in which line pictures were perturbed by omission or displacement of a combination of single pixels, fragments of lines, contours, and whole figures. Different effects of perturbation were expected by selectively violating visual syntactic rules or by impeding the contribution of certain feature detectors. The deterioration of the perturbed picture was measured according to standard psychophysical methods by rating on a 5-point scale. Multivariate methods were used to single out the relative effects of perturbation by, respectively, a set of single pixels, line fragments, contours and whole figures. Lines, as opposed to loose pixels, are clearly powerful descriptors of the pictures; contours or whole figures do not add significantly to what lines already describe. Different effects were observed if perturbations were dislocations rather than removals. Then contours and whole figures showed a typical disrupting effect compared to line fragments. These results have consequences for the development of a syntax of visual form perception. The perturbation method seems appropriate for identifying features or syntactic rules, although the results are dependent on a number of environmental and contextual factors.

Form Perception↗
PubMed1979

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↗
PubMed1992

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↗
PubMed1987

Finding parts within figures: a developmental study.

Preschool children, primary school children, and unschooled adults were tested on the part-probe task designed by Palmer. Relatively high scores were obtained with all groups on parts which had a 'good' relationship with the figure. However, the ability to find more deeply embedded segments was not present in the preschool children or in the unschooled adults. This indicates that the processes of postperceptual analysis necessary to find a part in a figure are neither built-in nor the consequence of mere cognitive growth, but depend on the instruction or experience usually provided in school. Such processes should not be confused with those that lead to form perception. Inspection of the part-figure pairs and of the corresponding detection scores suggests the importance of several stimulus properties.

Adult↗
PubMed1976

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↗
PubMed1985

Measurement and prediction of diagnostic performance during radiology training.

Faculty evaluations of residents' diagnostic performance in radiology subspecialty rotations were examined in two studies in order to ascertain whether the relative capabilities of residents change during training and to predict residents' diagnostic performance using a three-dimensional form perception test. In the first study, numeric ratings by faculty members were averaged to provide interpretive/diagnostic scores for each of 16 residents in each of 5 consecutive half-years. Sixty-seven percent of the relative differences among residents' diagnostic proficiencies persisted during training. The magnitude of these unchanging differences between individuals in diagnostic performance strongly favors resident selection based upon diagnostic potential. An additional 22% of the relative differences correlated with an abrupt change in the rank order of residents in diagnostic performance at the beginning of the second year of residency. This rearrangement of ranks may have resulted from an abrupt change in the tasks and expectations assigned to residents. In the second study, correlations between scores on a recently described Form Test and monthly faculty ratings of diagnostic performance were computed. An average diagnostic performance score for each resident was generated for all rotations combined, each of eleven subspecialties, and all rotations completed within a given half-year. Scores on the Form Test correlated well with these combined diagnostic scores, further substantiating results reported previously. Form Test scores were highly correlated with subspecialty diagnostic performance scores in subspecialties using cross-sectional imaging methods, such as neuroradiology. Although Form Test scores were poorly correlated with half-year diagnostic performance during the first year, they were highly correlated with performance beginning in the second year.

Educational Measurement↗
PubMed1990

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↗
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↗
PubMed1981

Perceptual processing strategies in the cross-modal transfer of form discrimination: a developmental study.

Groups of Grad 1, high school students, and elderly subjects were tested for their ability to discriminate tactile forms. The performance of control subjects who received no prior training was compared with that of subjects who received prior visual training under normal viewing conditions (Vw), or prior visual training with special goggles restricting form perception to a series of part impressions (Vp). Both the visual and tactile versions of the task involved comparisons of standard figures matched either with themselves or with transformation figures. There was no evidence of transfer for the children, regardless of previous experience. Specific as well as nonspecific cross-modal transfer was found in the high school and elderly groups following Vp training. Positive transfer was also found for the high school students in the Vw condition, although there is some question whether this was the result solely of cross-modal effects. Whereas all age groups performed equally well on standard versus transformation comparisons, standard versus standard matches were highest in the high school students, lowest in the children, and intermediate in the elderly. The generally poor performance of the children and the inability on the part of the elderly to benefit from Vw training are discussed in terms of task difficulty and inefficient perceptual processing strategies.

Adolescent↗