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 1,207 records · Page 67Linked to original sources
PubMed1991

Dynamic demonstration of proximal vergence and proximal accommodation.

The complex interactions between accommodation and vergence have been described by dual interactive models which include influences of convergence accommodation and accommodative vergence. Using an SRI Eyetracker, we investigated changes in vergence and accommodation stimulated while looking through prisms or lenses, and while looking at real targets located at different distances. Our results suggest that both proximal accommodation and proximal vergence are stimulated when looking from a distant to a near real target. We suggest that models of convergence and accommodation interactions include proximal accommodation and proximal vergence before the crosslinks.

Accommodation, Ocular↗
PubMed1996

The neural regions sustaining object recognition and naming.

This positron emission tomography study dissociates the neural correlates of object recognition and naming. Stimuli comprised coloured outline drawings of objects and coloured nonsense shapes. Subjects either viewed or explicitly named objects, similarly they viewed or named the colour of the shapes. Activations common to object and colour naming were identified by contrasting the explicit naming conditions (objects and colours) with the control (viewing) conditions. Activations associated with object recognition were identified by contrasting both object conditions (naming and viewing) with both shape conditions and activations specific to object or colour naming were identified by contrasting object naming (relative to object viewing) with colour naming (relative to shape viewing). The results associate: (i) object recognition with left middle occipital and bilateral anterior temporal cortices; (ii) modality independent naming with left posterior basal temporal lobe and the left prefrontal cortex; (iii) areas specific to object naming with left temporal extrasylvian regions, left anterior insula and right cerebellum; and (iv) areas specific to colour naming with left posterior lingual and fusiform gyri and midline cerebellum. These results are discussed in relation to previous neuroimaging and neuropsychological findings.

Adult↗
PubMed1997

Temporal hierarchy of the visual perceptive systems in the Mondrian world.

Our earlier psychophysical work has shown that colour and motion are not perceived at the same time, with colour leading motion by about 50-100 ms. In pursuing this work, we thought it would be interesting to use a more complex colour stimulus, one in which the wavelength composition of the light reflected or emitted from surfaces changes continually, without entailing a change in the perceived colour (colour constancy). We therefore used a Mondrian figure--an abstract multi-coloured scene with no recognizable objects--against which squares (either red or green) moved up and down, changing colour from red to green in various phase differences with the change in direction of motion. The red and green squares changed continually in their spectral characteristics, as did every other patch on the Mondrian. The results showed that colour is still perceived before motion, by about 80 ms.

Adult↗
PubMedDate not supplied

Generalizing the dynamic field theory of the A-not-B error beyond infancy: three-year-olds' delay- and experience-dependent location memory biases.

Thelen and colleagues recently proposed a dynamic field theory (DFT) to capture the general processes that give rise to infants' performance in the Piagetian A-not-B task. According to this theory, the same general processes should operate in noncanonical A-not-B-type tasks with children older than 12 months. Three predictions of the DFT were tested by examining 3-year-olds' location memory errors in a task with a homogeneous task space. Children pointed to remembered locations after delays of 0 s to 10 s. The spatial layout of the possible targets and the frequency with which children moved to each target was varied. As predicted by the DFT, children's responses showed a continuous spatial drift during delays toward a longer term memory of previously moved-to locations. Furthermore, these delay-dependent effects were reduced when children moved to an "A" location on successive trials, and were magnified on the first trial to a nearby "B" location. Thus, the DFT generalized to capture the performance of 3-year-old children in a new task. In contrast to predictions of the DFT, however, 3-year-olds' responses were also biased toward the midline of the task space-an effect predicted by the category adjustment (CA) model. These data suggest that young children's spatial memory responses are affected by delay- and experience-dependent processes as well as the geometric structure of the task space. Consequently, two current models of spatial memory-the DFT and the CA model-provide incomplete accounts of children's location memory abilities.

Attention↗
PubMed1986

Young children's knowledge about visual perception: projective size and shape.

Although recent research indicates that an increased sensitivity to visual appearances develops around 4 or 5 years of age, evidence from perceptual studies suggests that certain types of appearances, that is, projective size and shape, are not noticed or understood until at least 7. 4 experiments investigated preschool children's knowledge of the projective size--distance and projective shape--orientation relationships. In Experiment 1, 3- and 4-year-olds were asked whether an object should be moved farther or nearer in order to increase or decrease its apparent size. 4-year-olds performed significantly better than chance, but 3-year-olds did not. Experiment 2 showed that 3-year-olds are able to perceive projective size changes, indicating that although they do not fully understand the projective size-distance relationship, the necessary perceptual information is potentially available to them. In Experiment 3, 3- and 4-year-olds were asked to indicate how a circular object should be rotated to make it appear either circular or elliptical. Again, 4-year-olds performed significantly better than chance, but 3-year-olds did not. Again also, the results of Experiment 4 indicate that although 3-year-olds are not aware of the projective shape-orientation relationship, they are capable of attending to changes in projective shape. Thus, the constraints on children's knowledge of the projective size-distance and projective shape-orientation relationships seem to be at least partly cognitive rather than wholly perceptual. These results are interpreted as further evidence for the acquisition of level 2 percept knowledge during early childhood.

Child Development↗
PubMed1989

Attention to color: an analysis of selection, controlled search, and motor activation, using event-related potentials.

In this study the organization of information processing in a selective search task was examined by analyzing event-related potentials. This task consisted of searching for target letters in a relevant (attended) color. The ERPs revealed two different effects of attention: an early occipital negativity (+/- 150 ms) reflecting feature-specific attention, and a later, central N2b component (+/- 240 ms) reflecting covert orienting of attention. A later, prolonged negativity (search-related negativity) (+/- 300 ms), maximal at Cz, was related to controlled search to letters in the attended color. Detection of relevant targets resulted in a parietal P3b component. Depending on stimulus presentation conditions an earlier response to both attended and unattended targets was found: an N2 component (+/- 250 ms). In these same conditions, C'3-C'4 asymmetries (Corrected Motor Asymmetries--CMA) suggested motor activation at +/- 300 ms, in the same time range as search-related negativity. It was argued that N2 and CMA suggest the existence of a preattentive target detection system, operating in parallel with a slower serial attentive system, as reflected by N2b and search negativity.

Adult↗
PubMed1990

Interpersonal processes in dentistry. Part I.

An investigation of dentists' perceptions of their patients found that they were markedly similar to each other and to the perceptions other professional helpers have of their patients. It is suggested that this concurrence of perceptions reflects similar concerns about patients, in particular likeability, manageability, and prognosis. It has been established that several everyday person-perception processes work against forming favourable perception of patients and that this reduces the helpers' motivation to help them. In common with other professional helpers, these person-perception processes were evident in the perceptions of the dentists in this sample.

Adult↗
PubMed1975

Effect of length, density, and angel between arms of Gestalt grouping.

In three experiments, subjects viewed two lines (arms) of dots in which one dot was shared by both arms, then judged with which arm the shared dot appeared to group. Length of an arm, density of the dots in the arm, and angle between arms were manipulated. Increasing the density of an arm increased grouping with that arm regardless of the angle between arms. Increasing the length of an arm however, increased grouping when arms met at 30 degree but not at 180 degree; intermediate angles produced intermediate effects. Advantage of the present method's simplification of the stimulus display are discussed.

Distance Perception↗
PubMed1979

On the nature of difficulties in spatial-perceptual tasks: ethnic and sex differences.

The common claim that Africans exhibit a general weakness in handling spatial relationships is questioned, as is that of a general male superiority. The aim of the study was to identify some of the specific areas in which ethnic and sex differences may be located. A sample of 72 Ghanaian children evenly divided according to sex and early, middle and later stages of primary schooling were administered a series of tasks adapted from Piaget & Inhelder (1971); the same tasks were given to an equivalent group of Scottish children. On a block construction task involving memory the Ghanaians performed at the same level as the Scots when working from models, but not when the presentation consisted of photographs or line drawings (P less than 0.001). On two tasks requiring mental rotation of shapes and, subsequently, the actual assembly of shapes into regular figures, the Ghanaians again experienced more difficulty (P less than 0.001). Intercorrelation of scores on the various tasks suggested that the underlying structures of abilities may differ in Ghana and Scotland. The pattern of sex differences was exactly the same in both cultures. Girls did less well with the block construction (P less than 0.001), but there was no significant sex difference on mental rotation or shape assembly.

Adolescent↗
PubMed1979

Mental imagery and pictorial memory.

Previous research has failed to show consistent effects upon memory performance of individual differences in the use of mental imagery. A test of pictorial memory was devised which varied the ease with which the stimulus patterns could be verbally encoded. A factor analysis related performance in this task to a variety of other individual characteristics. The recall of material which could not be readily verbalized defined a factor within the solution which showed significant loadings of age and performance in the Progressive Matrices, but not of subjective ratings of the vividness of experienced imagery. The recall of material which could be readily verbalized did not contribute to the factorial structure of the results. It was concluded that the two sorts of pictorial material are remembered in quite different ways.

Adult↗
PubMed1979

Perception of simple figures: implicit-shape constancy and mental rotation.

Adults were shown simple figures either drawn on their own or on a face of a depicted cube. Under each of these conditions they were required to find identical figures in an array of stimuli of either the first or the second type. The response chosen determined the next stimulus used, the figures in both being identical. Four chains of 10 responses were thus obtained. Comparison of the choices reveals that the set consisting of 'plain' responses to 'cube' stimuli diverges significantly from the other three sets. This result is discussed in the context of other studies of implicit-shape constancy.

Adult↗
PubMed1994

Perceptual impulsions and unfamiliar solids: evidence from a drawing task.

Previous work (Dziurawiec & Deregowski, 1992) has shown that children's distorted drawings of animal models may be explained by the child's tendency to depict typical contours, the outlines of the surfaces which undergo pronounced change. The present paper investigates whether the typical contours notion can be extended to purely geometric solids. Results from a drawing task by children aged nine and eleven years, using unfamiliar models of varying complexity, indicate that the tendency to draw in perspective increases with the increase in figure complexity for both age groups, but younger children show a greater reliance on typical contours than older children. Recasting the data from previous drawing experiments (Bartel, 1928/1958; Cox, 1986) further confirms the utility of the typical contours approach. Finally, the advantages of such an approach over that of canonicity (cf. Palmer, Rosch & Chase, 1981) for the representation of solids are elaborated.

Child↗