A model of proximity measurement by the teleost nucleus isthmi

Nucleus isthmi (NI) in fishes, a visually responsive structure in the midbrain, has recently been proposed as a proximity detector, estimating the distance of approaching objects based on monocular motion cues. A model, consisting of 5 layers of linear summing units, was constructed to mimic the responses of tectum and NI in sunfish. The model responds to approaching rather than retreating objects, and generates activity that rises linearly during approach, indicating proximity, in large part independently of object speed and size.