Touchpoints reveal sensitivity to object shape in an individual with visual agnosia and in another who is cortically blind
Bibliographic record
Abstract
Object shape is exploited for object recognition and object-directed actions like reaching and grasping. Classic work has shown that information about object shape is expressed in the grasp kinematics and surface-contact points of individuals with compromised shape perception that followed damage to ventral-stream structures (e.g., Goodale et al. 1991). These studies constitute a cornerstone of the two visual systems hypothesis (Goodale & Milner, 1992) and its multi-visual-system descendants. Recent work with normally-sighted populations has shown that the freely chosen end points from point-to-touch movements directed at targets reveal the target-shape's medial axis – a type of shape 'skeleton' (Blum, 1973; Firestone & Scholl, 2014). Moreover, this occurs without participants' having any explicit knowledge of what a medial axis is or what it looks like (Firestone & Scholl, 2014). Here we ask whether or not this medial-axis phenomenon extends to exclusively dorsal-stream representations of shape, by testing DF, who has visual form agnosia resulting from lesions that encompass the shape-sensitive ventrolateral cortical area (LOC) bilaterally, and MC, who is cortically-blind following lesions that also encompass area LOC bilaterally. Each patient touched pebble-like shapes shown on a touchscreen in random positions and orientations. DF and MC could not reliably discriminate amongst the shapes in same/different, oddball, and 1-back tasks, confirming their deficits in visual shape perception. Nevertheless, both DF and MC manually localized the shapes with a high degree of accuracy, showing intact shape localization by the preserved dorsal stream. Moreover, DF's and MC's touchpoints each fell significantly closer to the centre-of-mass and the medial axis of each of the shapes, when compared to sampling distributions for squared- and absolute-mean-deviation metrics derived from random points. These findings indicate that, in addition to the centre-of-mass, other shape metrics such as the medial axis inform dorsal-stream mediated action in the absence of ventral-stream input. Meeting abstract presented at VSS 2018
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.003 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 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".