Contextual effects on the perception of stimulus dimensions
Bibliographic record
Abstract
A recent fMRI study has shown that the BOLD response to visual stimuli in human V1 is spatially nonlinear near the edge of the stimulated region (Shmuel et al, 2005, in Proceedings of the 11th Annual Meeting of the Organization for Human Brain Mapping, Toronto, 12 - 16 June). In particular, the activation extends significantly (ie about 1 mm) beyond the expected retinotopic mapping of the stimulus edge. However, it is unclear whether the corresponding increase in neuronal activity shows a similar nonlinearity and whether this nonlinearity biases our perception. Here, we have studied whether a visual stimulus that is spatially constrained by additional surrounding stimuli leads to a different percept than a stimulus that is presented on its own. We compared the perceived widths of bars with and without abutting flanks. High-contrast checker-bars flickering at 5 Hz were presented to four naive subjects. One bar flanked by bars flickering in counterphase and one non-flanked bar were shown simultaneously for 200 ms. The widths of both bars and flanks were varied randomly and the position jittered around an eccentricity of 6.8 deg. Subjects were instructed to fixate and to judge which one of the two bars had the larger width. A psychometric function was fit to the behavioural responses. Estimation of the point of subjective equality revealed that all subjects perceived the non-flanked stimulus as having a larger width. Over all subjects, the effect was about 0.3 deg of visual space, which corresponds to a cortical distance of about 1.3 mm (Brewer et al, 2002 Journal of Neuroscience 22 10416 - 10426). We conclude that the perceived dimensions of bars depend on the context of the visual stimulus. Whether this perceptual effect resembles previously found spatial nonlinearities in the BOLD response needs to be further studied.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| 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) | 0.007 | 0.003 |
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; both teacher heads agree on what is shown here.
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".