Test-retest reliability and Practice Effect of the Leuven Perceptual Organisation Screening Test

Visual diagnostic tests must have a high degree of consistency in its measurements (high reliability) to ensure accurate assessment of perceptual abilities. The current study assessed test-retest reliability and practice effects in Leuven Perceptual Organisation Screening Test (L-POST) in 144 healthy volunteers with time intervals between 0 and 756 days. We used correlation analysis, Bland-Altman analysis, and multi-level modelling. Results from our three analyses converged and supported an adequate reliability of L-POST. Multi-level modelling demonstrated an absence of practice effect, suggesting that the LPOST is suitable for repeat administration. This study suggests that Leuven Perceptual Organisation Screening Test has adequate reliability and is suitable for repeat administration even at short intervals. This study provides the basis for a more systematic evaluation for neuropsychological assessments, which can lead to the development of more reliable assessment batteries

Psychophysical and neuropsychological perspectives on perceptual organization with a focus on texture and contour processing

Organizing a visual scene in meaningful perceptual units, for example objects, is a necessary task for the visual system. Two important component processes of perceptual organization are texture segregation and contour integration. Texture segregation refers to the process by which two adjacent regions differing in texture become segregated from each other, as a result of which they are perceived as distinct texture patterns, often with a clear border between them. For instance, two adjacent trees in a garden can be segregated based on differences in texture. In contour integration, elements of a contour can be grouped according to the Gestalt principle of collinearity by aligning the orientation of elements along a smooth path. This is for instance necessary to reconstruct the contour of a partly occluded object. We have investigated both processes in two psychophysical and one neuropsychological study to learn more about the underlying mechanisms. In addition, a screening test to measure perceptual organization deficits in brain-damaged patients was developed and validated in the context of this doctoral thesis.In the first study, we have manipulated spatial arrangement of the elements in textures and concluded that spatial arrangement plays a role in a texture segregation task (requiring a shape judgment of the texture border) but not in a texture discrimination task (in which it is sufficient to discriminate a regular region from a completely random display). In the second study, we investigated the role of element orientation in shape encoding of contours. We found that shape encoding of contours with parallel elements (comparable to parts of contours that make up two sides of a branch) differs from shape encoding of contours with collinear elements (comparable to parts of a contour that make up one side of a branch covered by a leaf). In addition to the psychophysical experiments, we investigated these topics in a neuropsychological study with extinction patients. Due to parietal brain damage, these patients are usually not aware of stimuli presented in the contralesional hemifield, especially not when two stimuli are presented simultaneously. However, under certain conditions both stimuli can be integrated by grouping. We investigated if grouping in the context of texture segregation and contour integration is still intact in extinction patients and related their performance to intact or damaged brain areas. Besides the experimental studies, we applied our knowledge of perceptual organization in the development of the Leuven Perceptual Organization Screening Test (L-POST), a neuropsychological test in which a wide range of processes of perceptual organization are measured in 15 subtests. In clinical practice the L-POST can be administered to differentiate between mid-level deficits in perceptual organization and high-level deficits like object recognition for diverse patient groups (e.g., brain-damage, schizophrenia and autism). In addition, it offers a useful tool for researchers in identifying patients for neuropsychological research and to study age and developmental effects in perceptual organization. Reliability and validity of the L-POST were evaluated and data of a large norm sample were collected.nrpages: 202status: publishe

Data for 2 and 4 alternative forced choice disparity detection task

Data of 49 children completing a 2-AFC disparity detection task of 80 trials and 43 children a 4-AFC task. Accompanying the paper <i>Two choices good, four choices better: for measuring stereoacuity in children, a four- alternative forced-choice paradigm is more efficient than two,</i> by Kathleen Vancleef, Jenny Read, William Herbert, Nicola Goodship, Maeve Woodhouse, and Ignacio Serrano-Pedraza

Task differences in snake and ladder perception

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Component processes in contour integration: A direct comparison between snakes and ladders in a detection and a shape discrimination task

AbstractIn contour integration, a relevant question is whether snakes and ladders are processed similarly. Higher presentation time thresholds for ladders in detection tasks indicate this is not the case. However, in a detection task only processing differences at the level of element linking and possibly contour localization might be picked up, while differences at the shape encoding level cannot be noticed. In this study, we make a direct comparison of detection and shape discrimination tasks to investigate if processing differences in the visual system between snakes and ladders are limited to contour detection or extend to higher level contour processing, like shape encoding. Stimuli consisted of elements that were oriented collinearly (snakes) or orthogonally (ladders) to the contour path and were surrounded by randomly oriented background elements. In two tasks, six experienced subjects either detected the contour when presented with a contour and a completely random stimulus or performed a shape discrimination task when presented with two contours with different curvature. Presentation time was varied in 9 steps between 8 and 492ms. By applying a generalized linear mixed model we found that differences in snake and ladder processing are not limited to a detection stage but are also apparent at a shape encoding stage

Component processes in contour integration: A direct comparison between snakes and ladders in a detection and a shape discrimination task

In contour integration, a relevant question is whether snakes and ladders are processed similarly. Higher presentation time thresholds for ladders in detection tasks indicate this is not the case. However, in a detection task only processing differences at the level of element linking and possibly contour localization might be picked up, while differences at the shape encoding level cannot be noticed. In this study,we make a direct comparison of detection and shape discrimination tasks to investigate if processing differences in the visual system between snakes and ladders are limited to contour detection or extend to higher level contour processing, like shape encoding. Stimuli consisted of elements that were oriented collinearly (snakes) or orthogonally (ladders) to the contour path and were urrounded by randomly oriented background elements. In two tasks, six experienced subjects either detected the contour when presented with a contour and a completely random stimulus or performed a shape discrimination task when presented with two contours with different curvature. Presentation time was varied in 9 steps between 8 and 492 ms. By applying a generalized linear mixed model we found that differences in snake and ladder processing are not limited to a detection stage but are also apparent at a shape encoding stage.publisher: Elsevier articletitle: Component processes in contour integration: A direct comparison between snakes and ladders in a detection and a shape discrimination task journaltitle: Vision Research articlelink: http://dx.doi.org/10.1016/j.visres.2013.09.003 content_type: article copyright: Copyright © 2013 Elsevier B.V.status: publishe

Test-retest reliability and Practice Effect of the Leuven Perceptual Organisation Screening Test

Visual diagnostic tests must have a high degree of consistency in its measurements (high reliability) to ensure accurate assessment of perceptual abilities. The current study assessed test-retest reliability and practice effects in Leuven Perceptual Organisation Screening Test (L-POST) in 144 healthy volunteers using correlation analysis, Bland-Altman analysis, and multi-level modelling. Results from three analyses converged and supported an adequate reliability of L-POST. Additionally, multi-level modelling demonstrated an absence of practice effect, suggesting that the L-POST is suitable for repeat administration

Impaired texture segregation but spared contour integration following damage to right posterior parietal cortex

We examined the relations between texture segregation and contour integration in patients with deficits in spatial attention leading to left or right hemisphere extinction. Patients and control participants were presented with texture and contour stimuli consisting of oriented elements. We induced regularity in the stimuli by manipulating the element orientations resulting in an implicit texture border or explicit contour. Participants had to discriminate curved from straight shapes without making eye movements, while the stimulus presentation time was varied using a QUEST procedure. The results showed that only patients with right hemisphere extinction had a spatial bias, needing a longer presentation time to determine the shape of the border or contour on the contralesional side, especially for borders defined by texture. These results indicate that texture segregation is modulated by attention-related brain areas in the right posterior parietal cortex.status: publishe

Shortening the Leuven Perceptual Organization Screening Test With Item Response Theory and Confirmatory Factor Analysis

The Leuven Perceptual Organisation Screening Test (L-POST) is a test for mid-level visual perceptual deficits after brain injury. Previous research demonstrated reliable test scores and valid test score interpretations. However, the test’s duration (20-35 minutes) is too long for a screening approach for all patients in clinic practice. Our aim was to shorten L-POST to 10-15 minutes based on statistical criteria of the items. Data from 3391 participants who completed L-POST was analysed. L_POST consists of 15 subtests with 5 items each. Item Response Theory (IRT) was applied to guide the selection of the items. The highest correlation with full-scale subtest scores was observed when two items were selected for each subtest following an adaptive testing procedure. A pilot validation in a subsample of participants with low abilities demonstrated adaptive testing has reasonable sensitivity (80%) but limited specificity (55%) in classifying participants with impaired and unimpaired abilities. Subsequently, we reduced the number of subtests through factor analysis. We showed that the subtests using Radial Frequency Patterns as stimuli were redundant and could be combined in one subtest. We conclude that L-POST can be shortened to 26 items (7-14 minutes) and an adaptive item selection procedure could prove particularly useful for screening purposes