fMRI

fMRI measures changes in the brain’s blood flow and identifies, with spatial precision, which regions are more active during a task, from the BOLD effect. When a region works, the blood delivers more oxygen than it consumes, and it is that surplus the machine reads. It is an indirect signal twice over, because it measures blood rather than neurons, and because it tracks what arrives at a region better than what leaves it. It requires sophisticated equipment and a laboratory setting, but it returns a detailed map, including of structures such as the prefrontal cortexprefrontal 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 → and the nucleus accumbensnucleus 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 →. In UX, it has been used for what traditional methods cannot reach, such as the aesthetic impact the person is unable to report: the 2021 review by RuiRuiReviewed the EEG and fMRI studies on aesthetic processing in interfaces, which hold up the Emotion and aesthetics page.One reference in this work:2021A review of EEG and fMRI measuring aesthetic processing in visual user experience researchSee in the bibliography → and Gu gathers the studies linking aesthetic appreciation to the orbitofrontal cortexorbitofrontal cortexIt sits right behind the eyes and assigns value: whether the thing is worth it, whether it is pleasant, how much it costs in effort. It answers before the person knows they asked.See it in Emotion →See in the glossary →, associated with affective processing, and to the reward circuit, along with the visual cortex, which accounts for shape and colour.

Imaging results are read with a methodological caveat that almost never travels with the headline. Knowing that a region lit up does not allow you to conclude, working backwards, which mental process took place there. The same region takes part in very different things, and the inverted reasoning has its own name in the literature: reverse inference (PoldrackRussell PoldrackNamed the problem of reverse inference: seeing an area light up does not allow concluding which mental process is under way.One reference in this work:2006Can cognitive processes be inferred from neuroimaging dataSee on Wikipedia ↗See in the bibliography →, 2006). The finding supports the claim that judging something beautiful mobilises the circuits that assign value. It does not license the claim that there was aesthetic pleasure every time the orbitofrontal cortex shows up on a map.