A 66-year-old man, known as DN, experienced a sudden and dramatic change in his perception of the world after suffering a stroke in December 2017. The stroke caused an interruption in blood flow to the right posterior part of his brain, leading to a condition known as micropsia, where everything he saw appeared to be smaller by a third.
A World Shrunken by 30%
The impact of this condition on daily life was profound. DN found himself mistaking oversized shirts for his usual medium-sized ones. He perceived doors as smaller, potentially risking being trapped in the doorframe. He even thought his wife had washed the curtains with hot water, as they appeared to have shrunk.
By comparing familiar objects to his memory of their size, DN realized that everything around him had shrunk by approximately 30%.
A Rare Case of Right Posterior Brain Ischemic Stroke Leading to Micropsia
To understand why this happened, researchers at the University of Amsterdam, led by Nils van den Berg, conducted a series of tests on DN. One test involved DN estimating the size of 10 different cubes on a table in front of him. Based on his subjective experience, he estimated that each cube was about 30% smaller than what 11 other people saw.
This abnormal perception of size seemed to be related to DN’s left eye field of vision. For example, when he saw two adjacent and equally sized cubes, he believed the left one was smaller. Computer tests also showed that he had difficulties in identifying the shape, position, and movement of objects.
The Brain’s Attempt to Compensate for Damage
Van den Berg suggests that DN’s brain may be trying to balance the damaged left eye vision with the healthy right eye vision to compensate for the injury. So the result is a smaller, but uniform external world scene.
Other individuals with similar brain injuries have experienced seeing things smaller or larger than normal, or even upside down. However, the physiological mechanism behind this size distortion is still unclear.
Learning to Cope with Visual Distortion
DN has learned to cope with his visual distortion by comparing unknown objects to known ones. When he rides a bike or drives a car, he stays close to the side of the road to avoid colliding with oncoming vehicles. Van den Berg says, He gets easily tired, but on the other hand, his coping strategy is good.
This case illustrates how the brain uses information from various organs to create a coherent model of the external world.
The Theory of Size Distortion
Micropsia is a rare condition where patients perceive the world to be smaller than it actually is. It belongs to a group of disorders known as visual distortions, which may include seeing objects larger or smaller, perceiving straight lines as curved, distorted facial perceptions, or even upside-down vision.
Causes and Mechanisms
The causes of micropsia may be due to optical factors (such as wearing glasses), distortion of the eye image (such as corneal swelling or retinal shape changes caused by conditions like macular edema, age-related macular degeneration, or central serous chorioretinopathy), brain lesions (such as traumatic brain injury, epilepsy, migraines, prescription drugs, and illegal drugs), and psychological factors.
This condition is different from hallucinations or illusions, which occur when there is a temporary misunderstanding of a specific stimulus or situation in a complete perception. Visual distortions are the result of a missing or distorted sensory perception.
The Role of Brain Lesions and Visual Processing
Research has found that posterior temporal occipital lobe lesions are associated with micropsia. However, the exact location of the lesion in complete micropsia is still unclear.
The principle of size constancy requires that objects appear to be the same size regardless of the distance of observation. If this potential mechanism is disturbed in patients with microphthalmia, we hope they can perceive smaller objects at greater distances. However, this hypothesis currently lacks theoretical support.
The findings suggest that micropsia is more likely a high-level processing issue, especially when both hemispheres are affected.
The Role of Functional Competition
Another theory suggests that a unilateral brain injury leads to a conflict between the damaged right hemisphere and the healthy left hemisphere, causing a visual microparadox in the visual perception network. However, the details of this paradox’s potential mechanisms are still unclear.
The Research on DN’s Case
To quantify the degree of micropsia and study the patient’s grasp behavior, van den Berg and his team conducted three experiments. They also tested the visual function of both eyes to determine whether this condition affects both visual fields.
Finally, they found that although DN’s left eye field symptoms were more obvious at first, the symptoms seemed to involve both visual fields. Therefore, they concluded that DN’s unilateral posterior occipital lobe injury caused visual sensory
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