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PubMed1981

The effects of objective and perceived size properties on visual form matching.

The present experiments examined the effect of perceived size on the time it takes to make veridical form judgments. Recent studies have demonstrated an increase in the time required to match forms, as a function of increasing size, orientation, contrast, or color differences between the forms to be matched. The increase in reaction time to match forms has been explained by suggesting that form perception and matching is dependent on the degree of difference that exists in the objective size of the forms to be matched. This conflicts with the generally accepted view that form matching is independent of irrelevant proximal stimulus properties. The key to this issue seems to be whether form perception depends on objective or perceived stimulus properties. Studies in this area all involve manipulations of the objective stimulus properties, thus making it difficult to examine the effects of perceived properties. The current series of studies decoupled objective and perceived size differences by employing an illusion. The results demonstrated that the time to match forms is a function perceived differences in the stimulus forms, not the differences that exist in the objective size of the forms to be matched. In Experiment 1 three conditions were employed: a plain background condition in which the forms to be matched were objectively and subjectively equal in size, a double-illusion condition in which the forms were objectively and subjectively equal in size, and an illusion condition in which the forms were objectively equal in size but perceived as unequal in size. The results indicated a significant increase in reaction time for the illusion condition in which the forms were perceived to be different sizes, compared to the other two conditions in which perceived and objective size were equal. Experiment 2 results converged with and replicated those of Experiment 1. In Experiment 2 perceived size was equated for each subject in the context of the size illusion, thus varying the objective size of the stimuli. This manipulation led to a significant decrease in reaction time in this added condition, as compared to the illusion condition from Experiment 1 in which objective size was equal and perceived size differed. The results of Experiment 2 were replicated in a third experiment. Experiment 3 replicated the decrease in reaction time noted in the perceptually equal illusion condition. The decrease between illusion conditions was also approximated by an increase in a plain background condition with objective size differences. Thus the effect of perceived size accounts for the additional time to match forms of unequal size. The conclusion drawn from this series of experiments is that the time required to make veridical form judgments depends on perceived differences in the forms to be judged, not on the objective properties of the proximal stimulus. Implications of these results on models of pattern recognition are examined.

Discrimination Learning↗
PubMedDate not supplied

Age-related differences in visual perception: a PET study.

To assess age-related differences in cortical activation during form perception, two classes of visual textures were shown to young and older subjects undergoing positron emission tomography (PET). Subjects viewed even textures that were rich in rectangular blocks and extended contours and random textures that lacked these organized form elements. Within-group significant increases in regional cerebral blood flow (rCBF) during even stimulation relative to random stimulation in young subjects were seen in occipital, inferior and medial temporal regions, and cerebellum, and in older subjects, in posterior occipital and frontal regions. Group by texture type interactions revealed significantly smaller rCBF increases in older subjects relative to young in occipital and medial temporal regions. These results indicate that young subjects activate the occipitotemporal pathway during form perception, whereas older subjects activate occipital and frontal regions. The between-group differences suggest that age-related reorganization of cortical activation occur during early visual processes in humans.

Adult↗
PubMed1979

Influence of movement activities on shape recognition and retention.

Three groups of 4-yr.-old children were asked to complete a form perception assessment instrument prior to, 1 hr. after, and 1 wk. following a treatment. Group 1 participated in a movement-based form perception program, while Group 2 was instructed using a traditional classroom method. A third group which acted as control participated in unrelated movement activities. A repeated-measures analysis of variance gave a main effect of tests and an interaction of groups X tests. Group 2 displayed significantly higher performance on the posttest than Group 1; however, after 7 wk. the performance of Group 2 had decreased to a level below that of Groups 1 and 3, which remained stable.

Child, Preschool↗
PubMed2003

Contributions of the visual ventral pathway to long-range apparent motion.

Objects displaced intermittently across the visual field will nonetheless give an illusion of continuous motion [called apparent motion (AM)] under many common conditions. It is believed that form perception is of minor importance in determining AM, and that AM is mediated by motion-sensitive areas in the "where" pathway of the cortex. However, form and motion typically interact in specific ways when natural objects move through the environment. We used functional magnetic resonance imaging to measure cortical activation to long-range AM, compared to short-range AM and flicker, while we varied stability of structural differences between forms. Long-range AM activated the anterior-temporal lobe in the visual ventral pathway, and the response varied according to the form stability. The results suggest that long-range AM is associated with neural systems for form perception.

Brain Mapping↗
PubMed1996

Sensory dysfunction associated with repetitive strain injuries of tendinitis and focal hand dystonia: a comparative study.

Repetitive strain injuries are reaching epidemic levels among workers who perform heavy schedules of rapid alternating movements (eg., computer programmers, data entry workers) or repetitive, sustained, coordinated movements (eg., editors, writers, salespeople). The purpose of this study was to determine if patients with repetitive strain injury demonstrated degraded sensory motor performance with their hands. Sixty age-matched adults were recruited, with 15 each assigned to a healthy adult control group, a healthy musician control group, a tendinitis group, or a focal dystonia group. Four sensory motor subtests from the Sensory Integration and Praxis Test were given to the subjects according to a standardized protocol. Using multiple one-factor analyses of variance in the parametric or nonparametric mode followed by post hoc pairwise testing, no significant differences were found between the healthy controls and the musician controls. On the test of kinesthesia, using the left hand, subjects with tendinitis performed significantly worse than controls and subjects with focal dystonia. Compared with controls, subjects with focal dystonia did significantly worse on graphesthesia and manual form perception (part 1 and part 2). Subjects with focal dystonia also did significantly worse than subjects with tendinitis when using the left hand on graphesthesia and manual form perception (part 2). When treating patients with repetitive strain injury, discriminative sensory motor skills must be carefully assessed and may need to be addressed as part of an effective treatment program.

Adult↗
PubMed1981

Direction selectivity in human visual perception, investigated with low contrast gratings.

Velocity thresholds (VT's) of direction selective mechanism were measured with coarse low contrast gratings, visible only when moving. direction of movement was detected only in a movement perception domain (MPD), limited by upper and lower VT's and a minimum exposure time of movement. MPD expanded with increasing contrast or increasing stimulus area. MPD shifted towards higher velocities with lower spatial frequencies or with larger stimulus eccentricities. Form perception in MPD was best at optimal velocities; the spatial structure of the gratings was not evident at the VT level. These observations suggest a velocity tuned sensitivity of direction selective mechanisms and an association of movement and form perception with the activity of movement analysing neurons.

Differential Threshold↗
PubMed2002

Signals in macaque striate cortical neurons that support the perception of glass patterns.

Glass patterns are texture stimuli made by pairing randomly placed dots with partners at specific offsets. The strong percept of global form that arises from the sparse local orientation cues has made these patterns the subject of psychophysical investigations, yet neuronal responses to Glass patterns have not been studied. We measured the responses of neurons in macaque striate cortex (V1) to dynamic, translational Glass patterns as a function of dot separation and dot-pair orientation. Responses were selective, but were on average more than an order of magnitude weaker than responses to sinusoidal gratings. Response and selectivity were greatest when the dot-pair orientation matched that of the preferred grating and when dot separation was between one-quarter and one-half of the spatial period of the optimal grating; changing the dot-pair separation or inverting the contrast of one of the dots radically changed the orientation selectivity. We computed the expected responses for a receptive field model to translational Glass patterns and found that the complexity of our V1 tuning curves could be understood in terms of the responses of linear filters to pairs of dots. This modeling connects our understanding of V1 receptive fields as rectified, quasi-linear filters with results from psychophysical studies of Glass patterns. Our results provide a basis for studying how subsequent visual areas integrate weak, local signals into global form percepts.

Action Potentials↗
PubMed1978

The perception of solid form in early infancy.

Day and McKenzie determined the rate of habituation of fixation of young infants to repeated visual presentations of a cube. They found the habituation rate to be the same when the stimulus orientation changed between presentations as when it was fixed, and they interpreted this as evidence of shape constancy. However, a failure to discriminate between cubes in different orientations is only evidence of shape constancy if the infant can at the same time discriminate the cube from other cubelike forms. The experiment described here contrasted the rate of habituation of fixation of 12-week-old infants to a homogenous stimulus series (a cube presented in different orientations) with the rates of habituation to various heterogeneous series, in each of which a cube was alternated with some other solid. It was found that, while the infant could distinguish a cube from a photograph of a cube and a concave solid (an L-form), there was no evidence of discrimination between the cube and either a wedge or a truncated pyramid. The results imply limits to the young infants capacity to resolve solid form.

Discrimination Learning↗
PubMed2006

Development of visual motion perception in children of patients with schizophrenia and bipolar disorder: a follow-up study.

The "dorsal-stream vulnerability" hypothesis claims that motion-sensitive areas in the dorsal occipito-parietal visual system are vulnerable to genetic and environmental factors which affect brain maturation and development. The aim of this study was to investigate the possibility that developmental anomalies of directional motion perception can be detected in children of mothers with schizophrenia and bipolar disorder. Motion and form coherence thresholds were measured in 36 children of mothers with schizophrenia, 28 children of mothers with bipolar disorder, and 30 children with negative family history at 7, 8-9, and 10-11 years of age. These tasks require the detection of direction of coherently moving dots embedded among randomly oscillating dots (motion task) and the detection of tangentially oriented line-segments embedded among randomly oriented segments (form task). Results revealed that the rate of development in the motion task was less pronounced in children of mothers with schizophrenia than that in children of mothers with bipolar disorder and in age-matched controls. The development of form perception was spared. Children of mothers with bipolar disorder showed an intact development in both motion and form perception tasks. These results suggest that the progressive developmental abnormality of motion-sensitive visual areas may be a characteristic feature of schizophrenia-vulnerability.

Achievement↗
PubMed1985

Visual skills and intellectual development: a relationship in young children.

The development of convergence, ocular motilities; stereopsis and form perception for infants and young children was evaluated in a previous paper. This study examines the relationship between these visual skills and intellectual development. Young children (n = 130) were assessed longitudinally every six months from the ages of 12- to 42-months. The results showed positive and significant correlations between visual skills and intellectual development during infancy and the preschool years. Stereopsis and form perception correlated most highly and consistently with intellectual development.

Child Development↗
PubMed1987

Hemispheric asymmetries for complex visual patterns.

Three tachistoscopic studies examined the laterality of spatial-form perception in normal adults using randomly generated eight-point and 12-point patterns (Vanderplas & Garvin, 1959) as the lateralized stimuli. In the first study of recognition accuracy, 36 subjects were tested in a partial replication of Fontenot. No laterality effects were found, and over-all recognition was better for the more complex 12-point patterns. In a second similar study with 20 subjects, the lateralized stimulus was followed by a central masking pattern. A left-hemisphere superiority for recognition and better over-all recognition for more complex patterns was obtained. These data do not support Fontenot's report of right-hemisphere superiority in complex visuospatial processing. Given these diverse findings, a reaction time study using mental rotation was conducted using the same patterns to determine whether latency would reflect accuracy of recognition. Twenty-six subjects judged whether a rotated lateralized test pattern was the same or different from a central target pattern. Measures of both latency and accuracy were separately assessed. No main effect of visual field was obtained on either measure. These studies suggest that the nature of hemispheric involvement in spatial form perception is far from resolved.

Adult↗