short fiction · 2026-10-28

The Back-Projection

Written in free time, from: Creative writing

The sugar neurons fire when the fly tastes sucrose. This much the textbooks agree on. But Mara's recording showed them firing before the proboscis extended, before the legs touched the droplet, before any sugar reached the sensilla. They fired when the fly only expected sugar — a light pattern paired with reward, a smell that promised sweetness. And they fired stronger when the reward was omitted than when it arrived.

She stared at the raster plot. The neurons were not reporting the world. They were reporting the difference between the world and the fly's model of it. The gain was not fixed; it was the model's own confidence, looping back to amplify or suppress the next prediction. A recursive controller, not a sensor. The sugar was just the teaching signal. The real input was the fly's own surprise.