A Developmental Study of Size Constancy for Two-Versus Three-Dimensional Stimuli

1971 ◽  
Vol 42 (2) ◽  
pp. 633 ◽  
Author(s):  
Philip E. Kubzansky ◽  
Freda Rebelsky ◽  
Lynn Dorman
Keyword(s):  
Three Dimensional ◽  
Developmental Study ◽  
Size Constancy

scholarly journals Quantitative measurement of syndesmophyte volume and height in ankylosing spondylitis using CT

2013 ◽  
Vol 73 (3) ◽  
pp. 544-550 ◽  
Author(s):  
Sovira Tan ◽  
Jianhua Yao ◽  
John A Flynn ◽  
Lawrence Yao ◽  
Michael M Ward
Keyword(s):  
Ankylosing Spondylitis ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Reliability And Validity ◽  
Intervertebral Disk ◽  
Ct Scans ◽  
Developmental Study ◽  
Coefficients Of Variation ◽  
Spine Ct ◽  
Computer Based

ObjectiveSyndesmophyte growth in ankylosing spondylitis can be difficult to measure using radiographs because of poor visualisation and semiquantitative scoring methods. We developed and tested the reliability and validity of a new computer-based method that fully quantifies syndesmophyte volumes and heights on CT scans.MethodsIn this developmental study, we performed lumbar spine CT scans on 38 patients and used our algorithm to compute syndesmophyte volume and height in four intervertebral disk spaces. To assess reliability, we compared results between two scans performed on the same day in nine patients. To assess validity, we compared computed measures to visual ratings of syndesmophyte volume and height on both CT scans and radiographs by two physician readers.ResultsCoefficients of variation for syndesmophyte volume and height, based on repeat scans, were 2.05% and 2.40%, respectively. Based on Bland–Altman analysis, an increase in syndesmophyte volume of more than 4% or in height of more than 0.20 mm represented a change greater than measurement error. Computed volumes and heights were strongly associated with physician ratings of syndesmophyte volume and height on visual examination of both the CT scans (p<0.0001) and plain radiographs (p<0.002). Syndesmophyte volumes correlated with the Schober test (r=−0.48) and lateral thoracolumbar flexion (r=−0.60).ConclusionsThis new CT-based method that fully quantifies syndesmophytes in three-dimensional space had excellent reliability and face and construct validity. Given its high precision, this method shows promise for longitudinal clinical studies of syndesmophyte development and growth.

Apparent Depth and the Müller—Lyer Illusion

Perception ◽  
1973 ◽  
Vol 2 (2) ◽  
pp. 225-234 ◽  
Author(s):  
M A Georgeson ◽  
C Blakemore
Keyword(s):  
Three Dimensional ◽  
Apparent Depth ◽  
Size Constancy ◽  
Comparison Line ◽  
Perspective View ◽  
Lyer Illusion ◽  
Classical Size

The Müller–Lyer illusion was presented stereoscopically as either a flat or a three-dimensional figure. When the flat figure was made to appear closer or further than a comparison line, the illusion persisted along with large changes in overall size due to classical size constancy. When the fins of the figure were tilted in depth the illusion was somewhat reduced for both forward and backward tilts. It is argued that the size-constancy theory of illusions should predict an enhancement when stereopsis and the typical perspective view' reinforce each other, and abolition or reversal of the illusion when they are in opposition. These results therefore pose some problems for the theory.

The Cylinder Configuration: When is a Distortion an Illusion?

Perception ◽  
1983 ◽  
Vol 12 (5) ◽  
pp. 581-587 ◽  
Author(s):  
Michel Treisman
Keyword(s):  
Three Dimensional ◽  
Object Orientation ◽  
Perceptual System ◽  
The Other ◽  
Size Constancy ◽  
Lyer Illusion ◽  
Direct Association

A figure with one end rounded and the other concluding in an ellipse (the ‘cylinder configuration’) may appear longer than a rectangle of the same true length. It is proposed that when this configuration is processed as a three-dimensional body, it provides a cue for object orientation which causes the perceptual system to make an adjustment in the direction appropriate for maintaining size constancy. This effect may be considered a normal perceptual adjustment, appropriately applied. When the cylinder configuration is embedded in a context which does not favour its being processed as three-dimensional, a weaker adjustment in length may still occur. It is suggested that this effect, which may properly be classified as an illusion, may arise through direct association of the critical pattern of lines with the process of lengthening produced by the size-constancy mechanisms. Some relations of the present configuration to the Müller-Lyer illusion, and implications for the latter, are also discussed.

The Leaning Tower Illusion

2017 ◽  
Author(s):  
Frederick A. A. Kingdom ◽  
Ali Yoonessi ◽  
Elena Gheorghiu
Keyword(s):  
Three Dimensional ◽  
Size Constancy ◽  
Two Dimensional ◽  
The Relationship ◽  
Two Dimensional Images

The Leaning Tower Illusion is the illusion in which two identical images of the Leaning Tower of Pisa photographed from below, placed side by side, appear to rise at different angles. The illusion is not restricted to the Pisa tower however; it occurs in any pair of identical images of objects that appear to recede into the distance. This chapter argues that the illusion results from the misapplication of the visual system’s in-built mechanisms for correcting the distortions due to perspective in two-dimensional images of three-dimensional scenes. The relationship between the Leaning Tower illusion and size constancy illusions is discussed, and it is concluded that they are likely to be closely related.

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