Discriminating Global Orientation of Two Element Sets.

Perceived global organization of visual patterns is based upon the aggregate contribution of constituent components. Patterns constructed from multiple sources cooperate or compete for global organization. An investigation was made here of interactions between two interspersed element sets on global orientation.

Remediation of perceptual organisation in schizophrenia.

Introduction Impaired perceptual organisation in schizophrenia has been repeatedly described in clinical and research literatures. It has also been associated with problems in more complex aspects of visual function, including visuospatial and visual cognitive test performance. Two therapeutic interventions were developed here that target perceptual organisation: (1) Computer-based training, which emphasized stimulus-driven processing (bottom-up approach), and (2) Instrumental Enrichment therapy, which is a therapist-guided interactive learning method (top-down approach).

Lateral masking effects on contrast sensitivity in rats.

Changes in target visibility may be produced by additional stimulus elements at adjacent locations. Such contextual effects may reflect lateral interactions of stimulus representations in early cortical areas. It has been reported that the organization of orientation preference found in primates and cats visual cortex differs from that found in rodents, suggesting functional distinctions across species.

Effects of pattern masks on the formation of perceptual grouping.

Mechanisms underlying perceptual grouping serve to bind stimulus components that are contained within grouped patterns. In order to examine the time course of grouping development, grids of spatially isolated dots were followed by pattern masks across a range of SOA. Subjects indicated the predominant perceived grouping of the dot patterns.

Visual training improves perceptual grouping based on basic stimulus features.

Training on visual tasks improves performance on basic and higher order visual capacities. Such improvement has been linked to changes in connectivity among mediating neurons. We investigated whether training effects occur for perceptual grouping.

Effects of contrast, spatial frequency, and stimulus duration on reaction time in rats.

Early visual processing in rats is mediated by several pre-cortical pathways as well as multiple retinal ganglion cell types that vary in response characteristics. Discrete processing is thereby optimized for select ranges of stimulus parameters. In order to explore variation in response characteristics at a perceptual level, visual detection in rats was measured across a range of contrasts, spatial frequencies, and durations.

Priming effects on the perceived grouping of ambiguous dot patterns.

For ambiguous stimuli, complex dynamics guide processes of perceptual grouping. Previous studies have suggested two opposing effects on grouping that are produced by the preliminary stimulus state: one that enhances grouping towards the existing structure, and another that opposes this structure. To examine effects of the preliminary state on grouping directly, measurements were made of perceived grouping of dot patterns that followed a visual prime.

Perceptual grouping across eccentricity.

Across the visual field, progressive differences exist in neural processing as well as perceptual abilities. Expansion of stimulus scale across eccentricity compensates for some basic visual capacities, but not for high-order functions. It was hypothesized that as with many higher-order functions, perceptual grouping ability should decline across eccentricity.

Speed of perceptual grouping in acquired brain injury.

Evidence exists that damage to white matter connections may contribute to reduced speed of information processing in traumatic brain injury and stroke. Damage to such axonal projections suggests a particular vulnerability to functions requiring integration across cortical sites. To test this prediction, measurements were made of perceptual grouping, which requires integration of stimulus components.

Effects of Ketamine on perceptual grouping in rats.

Ketamine is a selective NMDA glutamate receptor antagonist that disrupts cognitive and behavioral function. Evidence exists that NMDA receptors play a role in lateral cortical connections, suggesting involvement in integrating information across the cortex. To investigate NMDA receptors' role in cortical integration at a perceptual level, psychophysical measures were made of perceptual grouping, which requires global analysis of neural representations of stimulus elements.

Computer programming for generating visual stimuli.

Critical to vision research is the generation of visual displays with precise control over stimulus metrics. Generating stimuli often requires adapting commercial software or developing specialized software for specific research applications. In order to facilitate this process, we give here an overview that allows nonexpert users to generate and customize stimuli for vision research.

Effects of visual cortex lesions on perceptual grouping in rats.

Neural mechanisms mediating perceptual grouping serve to enhance associations among stimulus elements, thereby establishing unified forms. The goals of the present study were to identify cortical areas necessary to perceptually group spatially isolated elements, and to determine if these areas are distinct from regions necessary for the discrimination of simple, solid forms. Rats were trained to discriminate horizontal and vertical lines that were either solid or composed of disjunct elements in which discrimination required perceptual grouping by proximity.

Perceptual organization by proximity and similarity in schizophrenia.

Perceptual organization represents a basic and essential function that occurs at an intermediate level of visual processing. Much of the previous research on perceptual organization in schizophrenia employed indirect measurements, or included factors beyond sensory processing. The aims of the present study were to determine the integrity of perceptual organization in schizophrenia, as well as to determine the stimulus duration necessary to perform perceptual organization.

Spatial-temporal characteristics of perceptual organization following acquired brain injury.

Objective: To assess characteristics of perceptual organization following brain injury.

Research Design: A repeated measures between groups design.

Methods: Perceptual thresholds were compared between 10 persons with brain injury and 10 demographically matched healthy control subjects.

Effects of aging on perceptual organization: efficacy of stimulus features.

Perceptual organization represents an intermediate level of visual processing, subordinate to higher-order processes such as object recognition. Previous studies of perceptual organization in aging are inconclusive, varying in the cognitive capacities measured and the nature of the stimulus. To determine characteristics of perceptual organization in aging, young and elderly participants discriminated patterns organized by basic visual components: line-orientation, color, flicker, or motion.

Effects of quinpirole on operant conditioning: perseveration of behavioral components.

Quinpirole (QNP) is reported to elicit repetitive spontaneous behaviors as well as reduce extinction of operant responses. To determine whether these effects represent perseveration of learned behaviors, behavioral components were examined during the acquisition and extinction of operant responses. Rats, receiving either 0, 0.

Effects of quinpirole on behavioral extinction.

Behavioral effects of quinpirole (QNP), a dopamine D(2) receptor agonist, suggest it impacts neural mechanisms mediating goal-directed behaviors, as well as behavioral extinction following removal of a primary reinforcer. The present study investigated the effect of QNP on behavioral extinction following the omission of contingent reinforcement, and whether this effect is related to acquisition or processes specific to extinction. Rats were trained on a continuous reinforcement schedule to nose-poke for water reward.

Perceptual organization based upon spatial relationships in Alzheimer's disease.

Alzheimer's disease (AD) is often accompanied by impaired object recognition, thereby reducing the ability to recognize common objects and familiar faces. Impaired recognition may stem from decreased efficacy in integrating visual information. Studies of perceptual abnormalities in AD indicate an impairment in organizing elements of the visual scene, thereby confusing components of individual forms.

Perceptual organization in Alzheimer's disease.

The ability of 16 AD patients and 16 age-matched control Ss to discriminate degraded forms was compared. Also examined were the effects of aging on perceptual organization by comparison of performance of normal Ss ranging in age from 20 to 86 years. Ss discriminated 2 forms, a circle and a square, each composed of randomly distributed dots concurrently embedded in visual noise.