Skip to content

Reference — photosensitivity literature

This is the evidence base behind the toolbox's flicker-safety warnings (src/ssvep/stim/flicker.py, surfaced in the Build run tab) and, for a deployment that operates under an ethics-board approval, behind that approval's photosensitivity sections too. Each entry states what the source says and what the toolbox does about it, so a reader can trace any threshold in the code to a citation.

Why there are no PDFs here. These are publisher-copyrighted works; redistributing them — including in a repository that will become public — is not permitted, and neither are the full-text web clippings that previously stood in for them. Every source below is cited by DOI or by its publisher's permanent link. Read them through your institutional subscription — no copy needs to live in this repository. Local copies of the governance documents that cite them belong on your institution's own secure storage, never in git.

All DOIs and bibliographic details below were verified against Crossref on 2026-09-12; the ITU Recommendation was verified against the ITU's own publication record.

The two thresholds the toolbox actually implements

flicker.py encodes exactly two facts from this literature, and nothing else:

Constant Value Source
PROVOCATIVE_LO_HZ / PROVOCATIVE_HI_HZ 3–30 Hz [2] sets the hazard floor at ≥3 Hz; [1] puts the provocative range at 1–65 Hz. The toolbox's 30 Hz ceiling is the study's own conservative bound, not a claim that 30 Hz is safe — see the caution below.
PEAK_LO_HZ / PEAK_HI_HZ 15–25 Hz [1]: "frequencies of 15–25 Hz are most provocative".

⚠️ The 30 Hz ceiling is a study design choice, not a literature finding. [1] reports a provocative range extending to ~65 Hz. The toolbox warns only up to 30 Hz because the approved protocol confines itself to 30–50 Hz stimulation, so anything above 30 Hz is out of scope for this study — not established as safe in general. Anyone adapting the toolbox for a different frequency range must revisit this constant against [1]; docs/REB_AMENDMENTS.md discusses the alpha-band (8–14 Hz) case, which sits below the peak but well inside the provocative band.

Risk in this literature is not frequency alone — it scales with luminance, contrast, the solid angle subtended, and pattern structure. [2] is the source of the quantitative limits, and the toolbox's warnings are deliberately advisory: they inform the designer, they do not gate the protocol, and the REB submission is where the full risk case is made.

References

[1] R. S. Fisher, G. Harding, G. Erba, G. L. Barkley, and A. Wilkins, "Photic- and pattern-induced seizures: A review for the Epilepsy Foundation of America Working Group," Epilepsia, vol. 46, no. 9, pp. 1426–1441, Sep. 2005, doi: 10.1111/j.1528-1167.2005.31405.x.

Relevance. The background review for the EFA consensus — the prevalence and dose-response evidence the toolbox's warnings rest on.

Key takeaways. - Photosensitivity (an abnormal EEG response to light or pattern) occurs in ~0.3–3% of the population; seizures from light stimuli ~1 per 10,000, or ~1 per 4,000 aged 5–24. People with epilepsy have a 2–14% chance of light- or pattern-precipitated seizures. - Frequencies of 15–25 Hz are most provocative; the range is 1–65 Hz. This is the direct source of PEAK_LO_HZ/PEAK_HI_HZ, and the reason the 30 Hz ceiling above is flagged as a study bound rather than a safety boundary. - Light–dark borders induce pattern-sensitive seizures; saturated red is an additional factor. - Photic or pattern stimulation provokes seizures in predisposed individuals but is not known to increase the chance of subsequent epilepsy — relevant to how risk is described on the consent form. - The Pokémon broadcast incident (685 children presenting to hospital) is the canonical case; notably 76% of those who seized had no prior seizure history, which is why screening cannot be the only control.

[2] G. Harding, A. J. Wilkins, G. Erba, G. L. Barkley, and R. S. Fisher, "Photic- and pattern-induced seizures: Expert consensus of the Epilepsy Foundation of America Working Group," Epilepsia, vol. 46, no. 9, pp. 1423–1425, Sep. 2005, doi: 10.1111/j.1528-1167.2005.31305.x.

Relevance. The operative one — the source of the quantitative hazard thresholds the toolbox's flicker limits derive from, and the closest thing this field has to a testable standard.

Key takeaways. - A flash is a potential hazard if it has luminance ≥20 cd/m², occurs at ≥3 Hz, and occupies a solid angle of ≥0.006 steradians (~10% of the central visual field, or ~25% of screen area at typical viewing distances). Source of PROVOCATIVE_LO_HZ. - Transition to or from saturated red is an independent risk factor. - A provocative pattern has more than five light–dark stripe pairs in any orientation, when it subtends >0.006 sr, the lightest stripe exceeds 50 cd/m², and it is shown for ≥0.5 s. If the pattern oscillates, flashes, reverses contrast or changes direction the limit is five stripe pairs; if unchanging or smoothly drifting, eight. - All three of frequency, area, and luminance must be exceeded together for the flash criterion to trip — which is the argument the protocol makes for small, frequency-multiplexed targets: subtended area, not frequency alone, is the lever the design pulls. - The consensus notes these principles are far easier to apply to fixed media than to interactive displays. An SSVEP experiment is fixed media in this sense — the stimulus is fully specified by the manifest before it runs, which is exactly why design-time validation is possible at all.

[3] A. J. Wilkins, C. E. Darby, and C. D. Binnie, "Neurophysiological aspects of pattern-sensitive epilepsy," Brain, vol. 102, no. 1, pp. 1–25, 1979, doi: 10.1093/brain/102.1.1.

Relevance. The primary work establishing that spatial pattern, independent of flash, provokes epileptiform discharge — the basis for the toolbox warning on checkerboard and grating stimuli, not just on luminance flicker.

Key takeaways. - Epileptiform response to gratings depends on spatial frequency, with a broad maximum near ~2–4 cycles/degree, and increases with the area of retina stimulated and with pattern contrast. - Binocular presentation is substantially more provocative than monocular. - Pattern sensitivity and photosensitivity overlap heavily in the same individuals, which is why the toolbox treats a patterned flickering target as carrying both risks rather than evaluating flicker alone.

[4] A. Wilkins et al., "A neurological basis for visual discomfort," Brain, vol. 107, no. 4, pp. 989–1017, 1984, doi: 10.1093/brain/107.4.989.

Relevance. The discomfort/aversion literature — the evidence that stimuli well below any seizure threshold still reliably cause headache, eyestrain and illusions. This is what the post-condition symptom questionnaire (docs/QUESTIONNAIRES.md) exists to capture, and it is the reason adverse-symptom monitoring is not optional in a long SSVEP session.

Key takeaways. - Striped patterns provoke illusions of colour, shape and motion in the general (non-epileptic) population, with the same spatial-frequency tuning that maximises epileptiform EEG response — suggesting a shared cortical mechanism. - Discomfort rises with contrast, duration, and the area of the visual field stimulated. - Susceptibility to pattern-induced discomfort is elevated in people prone to migraine, an exclusion/monitoring consideration for participant screening.

[5] International Telecommunication Union, "Guidance for the reduction of photosensitive epileptic seizures caused by television," Recommendation ITU-R BT.1702-3, Geneva, Switzerland, Nov. 2023. [Online]. Available: https://www.itu.int/rec/R-REC-BT.1702/en (PDF)

Relevance. The broadcast-industry codification of [2], and the standard commonly cited by ethics protocols covering this kind of flicker risk; useful mainly because it turns the consensus thresholds into measurable, testable acceptance criteria. ITU Recommendations have no DOI.

Key takeaways. - Restates the [2] limits as broadcast guidance and asks broadcasters to make producers aware of the risk of seizure-inducing content. - Recommends adaptive temporal filtering to attenuate frame-to-frame stimuli in the 10–30 Hz region, typically ≥20 dB at temporal frequencies of 10 Hz and above. - Annexes 1–5 carry the measurement methodology — the practical route to verifying a display's output rather than trusting the nominal design, which is the same job the flik-o-meter does for this toolbox. - ⚠️ Superseded revisions exist (BT.1702-1, -2). Cite -3 (11/2023); the ITU page above always resolves to the in-force version.

Governance sources (not reproduced here)

The ethics-board, TCPS2 and FOIPOP documents that bind this project are institutional records, not repository content — they live on this lab's own secure storage per its SOP, never in git. docs/COMPLIANCE.md (internal) states the enforceable rules derived from them for this deployment, and docs/REB_AMENDMENTS.md tracks divergences.

  • An ethics-board approval, where one governs this deployment — the approved protocol and its amendments, if applicable. Approval is evidenced only by the institution's own current record, never by a row in a markdown file.
  • TCPS2 (2022) — Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans. [Online]. Available: https://ethics.gc.ca/eng/policy-politique_tcps2-eptc2_2022.html
  • Nova Scotia Freedom of Information and Protection of Privacy Act. [Online]. Available: https://nslegislature.ca/sites/default/files/legc/statutes/freedom%20of%20information%20and%20protection%20of%20privacy.pdf