Posterior cortical atrophy: The effects on perception and action
Bibliographic record
Abstract
Posterior cortical atrophy (PCA) is a rare progressive neurodegenerative disorder that can target the occipital, temporal and parietal lobes. In early stages, PCA is characterized by impairments in higher level visual processing, while memory, language, and reasoning remain relatively intact. Symptoms can include problems in colour perception, face and object recognition, visually guided action, reading, writing, and problems seeing multiple objects in an array — depending on the location of atrophy. Here we present data from a 74-year-old woman, RB, who has been experiencing progressively worsening visual disturbances over the last 3 years. RB shows severe deficits in recognizing faces (including gender and race) and line drawings of common objects and, despite being a talented artist, she now has difficulty reproducing even simple line drawings. In particular, her deficits involve problems with integrating factors into a concept of the whole — she focuses her attention on one aspect or one detail of the visual form and then is unable to use additional features to form a holistic representation. RB has also experienced colour “hallucinations” where, for example, she has seen walls as different colours after closing and reopening her eyes, or sees colour in black and white pictures. Combined with MRI cortical analysis, these behavioural results suggest atrophy to the inferior temporal cortex, extending to the angular gyrus in the right hemisphere. Despite these severe perceptual difficulties, RB shows a relatively preserved ability in her visually guided action — properly scaling her grasp for object size and selecting stable grasp points on objects she is impaired at distinguishing perceptually. This case of “ventral” PCA reinforces the findings that there are separate visual pathways for visual perception and the visual control of action.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.012 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".