Sensory write via TMS-induced phosphene

The canonical non-invasive write channel for human BBIs delivers a bit by inducing a phosphene — a flash of perceived light — with transcranial magnetic stimulation (TMS) over the receiver's occipital (visual) cortex. A supra-threshold pulse produces a visible phosphene the receiver reports as 1; a sub-threshold or off-target pulse produces none, read as 0. Because the percept is conscious, the receiver knowingly participates, which is ethically and experimentally cleaner than covert stimulation.

This channel is deliberately minimal: it conveys essentially one discriminable event, its reliability depends on individually calibrated phosphene thresholds and coil placement, and it says nothing about the content of the sender's thought — only whether the pre-agreed symbol arrived. A different TMS target changes the write modality entirely: stimulating motor cortex evokes an involuntary movement instead of a percept (Rao and Stocco 2014), which bypasses the receiver's awareness and raises distinct agency concerns.