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At least 991 records · Page 55Linked to original sources
PubMed1995

Retinal, attentional, and causal aspects of illusory-motion directionality.

Extended objects presented instantaneously appeared to propagate or grow into their final shape. A strong bias was found toward perceiving straight lines to grow away from the observer's point of fixation. If attention and fixation were not directed to the same point of the visual field, both influenced illusory motion directionality, and if another small object was present on the screen at a location that was neither fixated nor attended to, the object that was instantaneously presented seemed to grow away from this point. Thus, three factors are involved in illusory-motion directionality: biases toward perceiving objects spreading away from the fixation point, away from an attended area, and away from preexisting objects. The experiments indicate that a satisfactory explanation of the illusion has to include bottom-up and top-down processes. They also challenge existing theories of motion detection.

Adult↗
PubMed1978

The relationship between perceptual dysfunction and language disorders: a case report.

The acquisition of language is discussed in relation to two specific perceptual processes: first, identification and discrimination of recurring aspects of an experience, and second, integration of the language form with the specific aspect of the event being represented. The analysis of the language of a child with perceptual and integrative deficits revealed expressive use of language without comprehension and limited knowledge of concepts. Explanations of these behaviors are presented in light of the child's perceptual and integrative dysfunctions. Implications for clinical management of a perceptually based language disorder are discussed.

Child↗
PubMed1998

Perceptual learning in visual search: some evidence of specificities.

To test a recent suggestion that perceptual learning in visual search is non-specific, two groups of subjects were trained on visual search tasks and tested for transfer of learning to new tasks. One group was trained on parallel ("pop-out") tasks and transferred to serial, conjunction tasks and the other group trained on conjunction and transferred to pop-out. Some (not all) tasks which are initially serial, rapidly became parallel. Some transfer occurred between the different types of tasks. Under some conditions transfer was either absent or even negative. The specificities observed may reflect the roles of the brain regions involved in learning.

Color Perception↗
PubMed2001

Neural response to perception of volume in the lateral occipital complex.

Projection of a 3D scene onto the 2D retina necessarily entails a loss of information, yet perceivers experience a world populated with volumetric objects. Using simultaneous behavioral and neural (fMRI) measures, we identify neural bases of volume perception. Neural activity in the lateral occipital cortex increased with presentation of 3D volumes relative to presentation of 2D shapes. Neural activity also modulated with perceived volume, independent of image information. When behavioral responses indicated that observers saw ambiguous images as 3D volumes, neural response increased; when behavioral data revealed a 2D interpretation, neural response waned. Crucially, the physical stimulus was identical under both interpretations; only the percept of volume can account for the increased neural activity.

Adult↗
PubMed2003

P3a from visual stimuli: typicality, task, and topography.

A visual three-stimulus (target, nontarget, standard) paradigm was employed in which subjects responded only to the target. Nontarget stimulus properties were varied systematically to evaluate how stimulus typicality (non-novel vs. novel) across task discrimination (easy vs. difficult) conditions affects P3a scalp topography. Nontarget stimuli consisted of letters, small squares, large squares, and novel patterns; discrimination difficulty between the target and standard was varied across conditions. When the discrimination was easy, P300 amplitude was larger for the target than the nontarget with parietal maximums for both. In contrast, when the discrimination was difficult, nontarget amplitude (P3a) was larger and earlier than the target P300 over the frontal/central electrode sites, whereas target amplitude (P3b) was larger parietally and occurred later. P3a was largest when elicited by either the large square or novel pattern stimuli. The findings suggest that stimulus context as defined by the target/standard discrimination difficulty rather than stimulus novelty determines P3a generation.

Adolescent↗
PubMed1989

Visual gap and offset discrimination and its relation to categorical identification in brief line-element displays.

Visual processing was investigated in judgments of relative line position. Stimulus continua were generated by bisecting a straight line and displacing the segments. Experiment 1 measured discrimination of pairs of longitudinally displaced segments at equal steps along the continuum. At long (2 s) durations discrimination fell smoothly, but at short (100 ms) durations it was sharp-peaked. In Experiment 2 the short-duration stimuli were labeled with subsets of the labels no gap, just a gap, and more than just a gap. Theoretical discrimination performances were computed and the one based on no gap and just a gap closely fitted observed performance. Experiments 3 and 4 were similar to 1 and 2, with lateral replacing longitudinal displacement. Similar "categorical" performance was obtained. It was concluded that there are discrete mechanisms for early detection of relative line position and that 2 labels can be used to characterize performance in each direction.

Adult↗
PubMed1977

Semantic and perceptual processes in symbolic comparisons.

This article studies the processing of pictures and words as symbols. Pictures lead to faster and more accurate responses than words when the task is to decide which member of a pair of pictures or words denotes the larger or smaller object. The present experiments show that the superiority of pictures results from the fact that pictures are interpreted more quickly than words, but that after the interpretation is made, processing is the same. These experiments also give evidence that pictures and words are both processed in terms of linguistic codes rather than mental images. The results are well accounted for by an information-processing model that is based on two general assumptions: (a) The stimuli and the instructions are represented as discrete codes, and (b) processing proceeds until one and only one of the stimulus codes is the same as the code for the instructions.

Discrimination, Psychological↗
PubMed1981

Individual differences in the classification of stimuli by dimensions.

In two experiments, adults differing in general mental abilities ("intelligence") were given multidimensional classification tasks: aural and visual free-classification tasks that allowed grouping of triads or trends by conflicting criteria of dimensional identity or overall similarity, and a speeded classification task that required the filtering of variation in an irrelevant dimension. Four principal results are reported: (a) Individual differences in the tendency to use similarity criteria in free classification were systematic across modalities and stimulus dimensions; (b) filtering performance, measured as the effect of irrelevant variation on speeded classification, did not correlate with free-classification performance (percent similarity responses); (c) the tendency to use similarity criteria in free classification was not correlated with intelligence; and (d) the amount of interference in speeded classification was correlated negatively with intelligence. The results taken together suggest that there are two dimensions of individual differences in perceptual analysis, one having to do with ability and the other with style or preference. This suggestion was supported by an additional analysis. The results also raise questions about the convergence of measures of multidimensional stimulus processing.

Discrimination Learning↗
PubMed1984

Modelling the stages of the identity theory of object-concept development in infancy.

A computational model is presented for the three stages of development of the object concept in infancy identified by Bower and Wishart in their research. The stages are described by sets of PROLOG clauses that interpret object structures representing the perceptual phenomena interpreted by the infants themselves. The infant's changes between developmental stages can be described by differences between the rules modelling each stage. Three experiments are presented and the behaviour of the PROLOG model is described for each stage of development. Motion, rest, and boundedness of objects constitute the theoretical underpinning of the running PROLOG model and are hypothesized as the invariant aspects of perception that explain the behaviour of the infant at each stage of development. A possible explanation for transitions between stages is offered and justified in part by the output of the model, which in turn is used to predict the behavioural outcome of an experiment.

Child Development↗
PubMed1988

Real and subjective contour Poggendorff illusions: no differences based on eye color.

Measures of illusion magnitude for a real contour and two subjective contour Poggendorff figures were obtained from a large number of dark-eyed and light-eyed undergraduates. Illusion magnitude varied as a function of figure type. However, eye color neither had a significant overall effect on illusion magnitude, nor did it interact with the figure-type variable. These data indicate that the presence of intersecting lines is not the basis of the iris-pigmentation effect reported by Coren and Porac.

Adult↗
PubMed1989

An orientation anisotropy in induced brightness.

It is shown that an orientation anisotropy exists for the magnitude of induced brightness in a cruciform stimulus consisting of a grey test patch positioned at the intersection of two inducing bars, one black and one white, oriented at right angles to each other. When the cruciform was oriented such that the white bar was horizontal, the grey patch appeared darker than when the same cruciform was oriented such that the white bar was vertical. The contribution of the black and white inducing bars towards the brightness of the test patch was investigated. A simple mathematical function, which took into account both the contribution of the two component inducing bars and the orientation anisotropy, was fitted to the data. No consistent orientation anisotropy was found with inducing stimuli at oblique orientations.

Attention↗