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Is the middle between both halves?: midpoint location and segment size estimation in neglect.
Alonso R Riestra1, Kyle B Womack, Gregory P Crucian
1National Center for Environmental Health of the National Institute of Public Health, Mexico City, Mexico. alonso_riestra@intramedios.com.mx
Neurology
|November 27, 2002
Summary
Patients with hemispatial neglect show greater errors in determining a line's midpoint ("where" task) than in comparing segment lengths. This suggests postperceptual deficits, not just size distortions, cause line bisection bias.
Area of Science:
- Neuroscience
- Cognitive Psychology
- Visual Perception
Background:
- Line bisection errors in neglect are often linked to perceptual size distortions.
- Accurate line bisection requires estimating a midpoint to compare line segments.
Purpose of the Study:
- To investigate if estimating a line's midpoint is dissociable from comparing segment lengths in neglect.
- To determine the relative contribution of these tasks to perceptual bias in neglect.
Main Methods:
- Two patients with right-hemisphere lesions causing hemispatial neglect were studied.
- Participants identified the location of bisection marks and compared adjacent line segment lengths on prebisected lines.
Main Results:
- A greater bias was observed in judging the position of bisection marks ('where' determination).
- The bias in 'where' determination was stronger than in comparing segment sizes.
Conclusions:
- Perceptual size distortion alone does not fully explain line bisection bias in neglect.
- Postperceptual deficits in 'where' computations, potentially involving attention and the dorsal stream, may better account for midpoint localization errors.