We Induced Smells With Ultrasound

Original Article ↗ Hacker News Discussion ↗

Overall Reaction

  • Many commenters find the experiment “breathtakingly cool” and love the hacker‑lab writeup style.
  • Others are intrigued but cautious, emphasizing that this is an N=2, self‑experiment blog post, not a peer‑reviewed result.

Plausibility, Mechanism, and Alternative Explanations

  • Several speculate that “burning”, “garbage”, “fresh air” etc. might be:
    • Direct olfactory bulb stimulation, or
    • Mechanical/thermal activation of existing gunk in the nasal cavity, or saturating receptors, analogous to seeing colors when pressing on your eyes.
  • COVID parosmia, stroke, and other disorders are cited as examples where a wide range of inputs collapse into a few “bad” odors, supporting the idea that much of olfactory space may default to “danger” smells.
  • Vibration theory of olfaction and receptor “resonance” are mentioned; others note the ultrasound frequency is far from molecular vibrational modes, so the exact mechanism remains unclear.

Safety and Legality

  • Multiple commenters ask “is this safe?” and whether it’s legal off‑label device use.
  • One of the experimenters replies: power levels were measured with a hydrophone and kept well below diagnostic ultrasound limits; mechanical index was ~0.4 vs. the 1.9 guideline.
  • Some remain uneasy about intentionally focusing energy at the brain and draw parallels to concerns about high‑powered prenatal ultrasound; others push back that standard scans are well‑studied and this setup requires precise targeting not present in routine imaging.

Scientific Rigor and Replication

  • Critiques include:
    • Very small sample size, both subjects being authors.
    • Lack of institutional affiliation, formal protocol, or deep engagement with prior literature.
    • Strong wording like “turns out, yes!” and “no one has done this” viewed as premature.
  • Defenders call it reasonable transcranial focused ultrasound (TFUS) with a novel target and see it as valuable “citizen science” that should now be independently replicated.

Applications and Speculation

  • Suggested uses:
    • VR / gaming / “smell‑o‑vision”, especially in porn and immersive media.
    • Advertising, crowd or riot control, nuclear‑waste warnings, code‑review “code smell” tools.
    • Neuromodulation beyond smell: vestibular stimulation, mood, learning aids.
    • Therapeutic and diagnostic uses for anosmia, olfactory rehab, and maintaining expertise (e.g. sommeliers).
  • A particularly discussed idea: olfaction as a ~400–800‑dimensional input channel, potentially used to “write” high‑dimensional semantic vectors (like LLM latent space) directly into the brain.

Ethical and Societal Concerns

  • Strong distrust of large tech firms having “direct write access” to the brain; some argue we already grant such power to social media behaviorally.
  • Calls for any future high‑resolution brain‑writing tech to be open‑source and auditable, to avoid opaque, potentially manipulative devices controlling perception.