Spatial distortions in localization and midline estimation in hemianopia and normal vision

Area of Science:

• Neuroscience
• Visual Perception
• Ophthalmology

Background:

• Individuals with hemianopia often demonstrate a bias in line bisection tasks, directing the bisection towards their blind visual field.
• A leading theory posits that this hemianopic line bisection error (HLBE) results from a perceptual distortion, specifically an expansion of central visual space.

Purpose of the Study:

• To investigate whether perceptual expansions of central visual space occur in the intact hemifield and are observable across different tasks.
• To validate novel tasks for assessing perceptual asymmetries in healthy individuals and those with visual field loss.

Main Methods:

• Neurologically healthy participants completed a peripheral localization task and a novel midpoint assessment task.
• Two patients with hemianopia were tested using the peripheral localization task across horizontal and vertical axes.
• The peripheral localization task involved judging a target dot's position relative to the perceived visual field boundary.

Main Results:

• Individual biases in line bisection and midpoint estimation were consistent in healthy participants.
• Results indicated that the hemianopic line bisection error is associated with an expansion of perceived space along the spared temporal axis.
• The study validated the peripheral localization and midpoint assessment tasks for exploring visual field perception.

Conclusions:

• The hemianopic line bisection error is likely caused by an expansion of perceived visual space along the spared temporal axis.
• The developed tasks are effective tools for studying perceptual asymmetries in visual field loss and healthy individuals.