Looking at the Ebbinghaus illusion: differences in fixations fail to explain a classic perception-action dissociation
Bibliographic record
Abstract
Visual recognition and visually-guided action present an animal with different computational requirements. Take, for example, changes in the retinal image of an object that occur with changes in the spatial relationships between the object and the observer. This retinal variation matters when reaching for the object, because estimates of the spatial relationships that drive it are useful for coding appropriate limb motor commands. At the same time, this variation must be filtered-out to extract the object’s invariant features and associate those features with stored semantic correlates. An organism with multiple visual areas for object coding can afford specialized operations to suit different cognitive and behavioural endpoints. Pictorial size-contrast illusions like the Ebbinghaus display, which influences the perceived sizes of disks embedded in it, have offered behavioural vision scientists a controversial vehicle for exploring the functional organization of human vision; in a now classic dissociation, the hand’s in-flight grasp aperture, which normally scales to target size, resists the Ebbinghaus display's influence on perceived disk size. An alternative account posits that grasp aperture resists the illusion because participants fixate on the target disk and ignore the illusion-inducing context. To test this account, we tracked both hand movements and gaze while participants made forced-choice judgments of relative disk size in the Ebbinghaus display or did so in combination with grasping or perceptually estimating the sizes of the illusory disks. We replicated the classic dissociation: grasp aperture was refractory to the measured illusory effect on perceived size, while judgments and manual estimates of disk size were not. Importantly, the number of display-wide saccades per second and the percentage of total fixations directed at the selected disk (in time and number) failed to explain the dissociation. Our findings support the contention that object perception and goal-directed action rely on distinct and parallel coding for objects.
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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 | 0.005 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".