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Visual imagery deficits in posterior cortical atrophy

DOI: 10.1080/02643294.2024.2346362
Dietz, C. D., Albonico, A., Tree, J. J., & Barton, J. J. S. (2023). Visual imagery deficits in posterior cortical atrophy. Cognitive Neuropsychology, 40(7-8), 351–366. doi:10.1080/02643294.2024.2346362

Abstract

Visual imagery has a close overlapping relationship with visual perception. Posterior cortical atrophy (PCA) is a neurodegenerative syndrome marked by early impairments in visuospatial processing and visual object recognition. We asked whether PCA would therefore also be marked by deficits in visual imagery, tested using objective forced-choice questionnaires, and whether imagery deficits would be selective for certain properties. We recruited four patients with PCA and a patient with integrative visual agnosia due to bilateral occipitotemporal strokes for comparison. We administered a test battery probing imagery for object shape, size, colour lightness, hue, upper-case letters, lower-case letters, word shape, letter construction, and faces. All subjects showed significant impairments in visual imagery, with imagery for lower-case letters most likely to be spared. We conclude that PCA subjects can show severe deficits in visual imagery. Further work is needed to establish how frequently this occurs and how early it can be found.

Authors

  • Connor D. Dietz1
  • Andrea Albonico1
  • Jeremy J. Tree1
  • Jason J. S. Barton1

What This Study Is About

Researchers wanted to summarize everything we know about a rare condition called Posterior Cortical Atrophy (PCA). It is often called the "visual variant" of Alzheimer’s because, instead of starting with memory loss, it begins by damaging the parts of the brain that process what we see and how we "see" things in our minds.

How They Studied It

This was a "review paper," which means the authors didn't just run one experiment. Instead, they acted like detectives, gathering and analyzing decades of research involving hundreds of patients. They looked at brain scans (MRIs), specialized imaging that shows brain energy use (PET scans), and various vision and memory tests to map out how this condition works.

What They Found

The researchers found that PCA specifically attacks the "back" of the brain (the posterior cortex). This area acts like a computer's graphics card. When it’s damaged, people experience strange visual glitches even though their eyes are perfectly healthy:
  • Simultanagnosia: This is like looking at the world through a straw. A person might see a single tree clearly but be unable to "see" the entire forest.
  • Object Agnosia: People might see an object but be unable to identify what it is just by looking.
  • Mental Imagery: Because the damage happens in the brain's "visual hub," these patients often lose their mental imagery—the ability to picture things in their mind's eye.

What This Might Mean

For the aphantasia community, this research is a big deal because it confirms which "hardware" in the brain is responsible for creating internal images. It suggests that if the back of the brain isn't communicating properly with the front, the "screen" in our mind stays blank.
A note of caution: This study focused on people *losing* their imagery due to disease. This is different from "congenital aphantasia" (being born without a mind's eye). While the brain areas are the same, the reasons for a blank "mind's eye" in a healthy 15-year-old are likely very different from those in a PCA patient.

One Interesting Detail

Some people with this condition experience a "reverse-size" phenomenon: they find it much easier to read tiny print than giant headlines because their brains can no longer "zoom out" to see large shapes!
This summary was generated by AI and may contain errors. Always refer to the original paper for accuracy.