A comparison of the BOLD fMRI response to achromatic, L/M opponent and S-cone opponent cardinal stimuli in human visual cortex: I. perceptually matched vs contrast matched stimuli
Bibliographic record
Abstract
Aims: Our primary aim was to compare the responsiveness of the different visual cortical areas to stimulation of the two cone opponent systems and the achromatic system. The appropriate contrast metric for the comparison of color and luminance sensitivity is unknown, however, and so our secondary aim was to investigate whether equivalent fMRI responses of each cortical area could better be predicted from perceptual matches (in multiples of detection threshold) or a direct contrast match (in cone contrast). Methods: MR images were acquired on a 4T Bruker MedSpec. Stimuli were sinewave counter-phasing rings (2Hz, 0.5cpd) cardinal for the selective activation of the L/M cone opponent (RG), S cone opponent (BY) and achromatic (Ach) systems. In different scans, stimuli were matched either at 25x detection threshold or in cone contrast (6%). We performed both stereotaxic and region of interest analyses on early visual areas (V1–V4v, and hMT+). Results: For stimuli presented in multiples of detection threshold, BOLD responses in areas V1, V2, V3/VP and V4v are greatest for BY stimuli and weaker for both RG and achromatic stimuli, with the BY response significantly higher than the RG. For the same stimuli matched in cone contrast, the RG and BY response is similar in these areas. The averaged color response (RG & BY) was no different from the achromatic response with the exception of V1, which had a greater averaged color than achromatic response. Conclusions: Perceptual visibility is not a good indicator of cortical activity across the RG, BY and achromatic mechanisms. fMRI BOLD signals are better predicted by cone contrast. Regardless of the metric, our data suggest a similar response to color (averaged RG & BY) and achromatic stimuli in V2, V3, VP and V4v. V1 shows a greater response to color, particularly with the cone contrast metric. Areas hMT+ and V3A do not follow these patterns and are discussed in a related abstract (Dumoulin et al).
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".