Evidence for a functional and anatomical dissociation in the use of size constancy for perceptual report and goal-directed grasping
Bibliographic record
Abstract
On a moment-to-moment basis, we experience the visual world as permanent and unchanging despite the fact that the retinal image size of objects in the scene change with changes in viewing distance. After all, to the ‘naked eye’, the real size of objects rarely changes over short time scales and our visual system faithfully delivers this experience in terms of visual object-size constancy. Arguably, visual size constancy operates during prehension as well: objects can vary in retinal image size at different positions within reachable space and yet the visuomotor system codes grasping movements on the basis of the target’s real size. Previous evidence from our laboratory, however, suggests that visual size-constancy for perception and for goal-directed grasping are not unitary. Here, we demonstrate conclusively that visual size constancy for perception and for grasping are functionally and anatomically dissociable. We tested a cortically blind patient, MC, who has large bilateral lesions encompassing almost the entire occipital lobe. We first demonstrate that MC's verbal and manual reports of target size depend entirely on retinal image size. Next, we show that despite MC’s reliance on retinal image size for explicit reports of target size, her grasps are tuned to trial-to-trial changes in the real size of the targets – even when their retinal image size remain constant. Critically, for both perceptual report and grasping, the targets were presented at eye level in the absence of any environmental cues. We conclude that MC’s spared size-constancy for prehension depends on the dorsal visual pathway’s privileged access to shifts in horizontal gaze angle and/or accommodation to calibrate her grasps. Meeting abstract presented at VSS 2015
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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 | 0.001 | 0.008 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.002 | 0.000 |
| Science and technology studies | 0.000 | 0.006 |
| Scholarly communication | 0.001 | 0.002 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.002 | 0.002 |
| Insufficient payload (model declined to judge) | 0.006 | 0.000 |
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".