Body reading
Functional near-infrared spectroscopy
fNIRS
Measures: The cortex’s oxygen consumption during the task, outside the laboratory
It is the brain imaging that fits in a cap and copes with the person sitting in their usual place, using their own phone. If an imaging study is ever run on your actual product, rather than on a mock-up inside a tube, it will be with this one.
fNIRS shines infrared light onto the scalp and measures how much light comes back. Because oxygenated and deoxygenated blood absorb that light differently, it is possible to track the cortex’s oxygen consumption, the same phenomenon fMRI measures, by a much cheaper route. The difference that matters here is practical: the equipment is wearable, tolerates movement and works with the person standing, walking, driving or using the product in its real context, things fMRI forbids (PintiReviewed the use of fNIRS in cognitive neuroscience, the method that allows measuring the brain with the person standing and moving.One reference in this work:2020The present and future use of functional near-infrared spectroscopy (fNIRS) for cognitive…See in the bibliography → et al., 2020). The first price is reach. The light travels only a few centimetres and reaches only the cortex, so deep structures such as the amygdalaTwo small structures in the temporal lobe that decide, in milliseconds, whether something is a threat or an opportunity. They respond to your screen before any conscious judgement about it.See it in Emotion →See in the glossary → and the nucleus accumbensThe centre of the reward circuit. When something goes right — a button that responds, a task that closes — it is what records “worth it, do it again”.See it in Emotion →See in the glossary → remain invisible. For cognitive load in the prefrontal cortexThe region behind the forehead, where the person decides, plans and sustains attention. It keeps one thing in focus at a time and inhibits the rest: it is where the bottleneck of conscious decision usually tightens.See it in Memory →See in the glossary →, which is the most common question in design, that is usually enough.
And there is a second price, which matters more to this site. The signal depends on the light reaching the scalp, and coily or dense hair and more melanated skin attenuate the reading, which in practice has been excluding Black participants from studies. Of 87 fNIRS papers published between 2017 and 2022, none reported skin tone (KwasaOne reference in this work:2023Demographic reporting and phenotypic exclusion in fNIRSSee in the bibliography → et al., 2023).
SeesHaemodynamic imaging in the field, with the person free to move.
Does not seeIt only reaches the surface, and sees coarsely: it resolves in the range of two to three centimetres, against millimetres in fMRI, and with no anatomical image underneath.