Brain or Skin? Experiments That Can Settle the Question Around Deepinder Goyal's Temple Wearable

A temple-worn wearable shows a Brain Flow number from a light sensor. A public argument asks whether such a sensor can see blood flow inside the brain, or only in the skin and the artery outside the skull. The studies posted so far show that the number rises and falls with blood flow when a person stands up, lies down or cycles. But skin blood flow also moves in these tests, so a match does not show where the signal comes from. This note sets out five experiments that can settle the question. They are: pressing the artery that feeds the skin, a second sensor that reads only the skin, a supervised change in the carbon dioxide of the breath, records of blood pressure and breathing, and a same-side Doppler check on more kinds of people. The note adds one more check that needs no secret from the maker. The same recording is read at several of the device's own settings, and the spread of the numbers tells whether the number is firm. Because skin, hair and the fit of the sensor differ from person to person, the right setting for each person is found in the first few hours of use, or at most the first two days, by a computer-decided shunting action. This action moves the device from one setting to another, without waiting for a person, until the spread is narrow. The same action finds a new setting if something changes later. If the spread is wide, the wearer sees a calm message instead of a confident number. The note also asks how fast the number returns to normal after a change of posture, and explains in plain words how this differs from Bayesian networks and Monte Carlo dropout. Patent pending. Keywords: wearable, brain blood flow, near-infrared sensing, superficial temporal artery, firmness of a reading, spread across settings, shunting action