No description available.

No description available.

A forced-choice reaction time (RT) task was used to examine the development of visual filtering. Specifically, this study examined whether visual filtering is more efficient in smaller spatial ranges, and the extent to which age-related changes in filtering efficiency could be attributed to improvements in the ability to expand and contract an attentional focus. Participants included 20 children in each of four age groups (4, 5, 7, and 9 years), as well as 20 adults aged between 20 and 29 years. Conditions varied with regard to the location or presence of distracters, and the presence of a window within which target stimuli were presented. RT's were slower in the presence of distracters located within one 1 degree of visual angle from target stimuli than when distracters were presented 5.7 degree of visual angle away. In addition, young children were less capable than either older children or adults to filter task-irrelevant stimuli. With regard to the window, RT's were faster in the presence of a window than in its absence. Finally, the window was most effective in improving the filtering efficiency of 4 year old children. These results are discussed in terms of the zoom-lens metaphor of visual attention, and the development of the ability to vary the size of an attentive zoom-lens in response to task requirements.

The change blindness phenomenon, which is described as changes in the environment that are missed under natural viewing conditions because they occur simultaneously with another visual disruption, was studied from a developmental perspective. Participants included a total of 65 children in 3 age groups, 6, 8, and 10 years, and 20 adults, who were administered a version of the flicker paradigm, a technique in which blank screen is inserted between presentations (Rensink, O'Regan, & Clark, 1997). Participants responded to multiple presentations of 2 objects, positioned side by side, displayed on a computer screen. In each presentation, a distracter object remained unchanged, whereas the target object changed in 1 of 3 ways, color switch, missing part, and rotation. Stimuli consisted of inanimate objects, photographs and drawings, and were displays in either 50 milliseconds or 250 milliseconds. Results revealed that 6 years old participants displayed the highest degrees of change blindness.

A single case study of a brain damaged patient with a category-specific visual agnosia for living things is described. The patient's deficit is manifested as a profound inability to identify, label or classify biological visual objects at the basic level. Most similar cases in the literature have been described as due to damage to a pre-categorical structural description system. However, all these cases also displayed content-specific impairments in activating knowledge from words. ELM's ability to activate basic-level knowledge from pictures and words is investigated using accuracy-based and chronometric measures. The pattern of ELM's category-specific visual agnosia is concomitant with his failure to show priming and typicality effects for words. This suggests that ELM's deficit resides within the semantic memory system. Tests of the integrity of structural descriptions reveal that this patient retains implicit access to pre-categorical structural knowledge.

Since Miskin and Forgays, lateralized differences in visual information processing has largely been explained by models consistent with theories of hemispheric specialization. The present study offers an alternative explaination to account for visual half field asymmetries while elucidating past methological inadequacies characteristic of many visual half field studies.Response times and accuracy scores were examined as a function of visual half fields and visual encoding strategies. All subjects responded manually to unilateral tachistoscopic stimulus presentation. Subjects were tested under two strategy conditions: (1) subjects responded to verbal stimuli using a verbal (linguist) encoding strategy, and (2) subjects responded to verbal stimuli using a non-verbal (visio-spatial) encoding strategy.Results were consistent with earlier studies which report a right visual half field superiority to unilateral presentation of verbal stimuli. Significant differences were noted between visual half field presentation and strategy conditions. Results are discussed in terms of an alternative explaination to account for visual half field asymmetries, based heavily upon methodological considerations and visual stimulus information encoding strategy.

There is no abstract available for this thesis.

No description available.

No description available.

The effect of perceptual load and target-flanker proximity on developmental patterns of filtering efficiency was examined among children 5-12 years and a group of adults. The participants were asked to respond to a centrally presented arrow surrounded by congruent or incongruent flanker arrows. Filtering was operationalized in terms of the flanker congruency effect (FCE) and measured as the response latency difference between trials with incongruent flankers versus trials with congruent flankers. Conditions varied with regard to target-flanker distances and levels of perceptual load. Developmental changes in susceptibility to the FCE did not appear to be related to target-flanker proximity, but were related to a perceptual load manipulation that involved varying the response associated with the target. The FCE was larger in magnitude for 7-10 year old children than for 11-12 year old children and adults under low perceptual load conditions. However, these developmental differences in susceptibility to the effects of interference were no longer apparent under high perceptual load conditions. This finding suggests differential developmental trajectories for filtering efficiency based on the processing demands involved in the task, and can be understood within the framework of the perceptual load model of selective attention.