If startled in a narrow environment, wild-type flies run toward a light source in order to initiate an escape flight. The response of tay¹ homozygous flies in assays designed to test this response is significantly slower than wild-type flies. In negative geotaxis assays, these flies walk, on average, only 1/9th the speed of wild-type flies. In a Buridan's paradigm assay, these mutants walking activity is less than half that seen in wild-type flies and walking paths are less straight. However, their response is still directional in this assay, indicating that they can see and respond to visual stimuli. Consistent with this, they are also capable of optomotor compensation during walking - as assayed by their walking tracks when surrounded by a rotating grating. However, their degree of optomotor compensation in this assay is significantly less than wild-type.

The protocerebral bridge in tay¹ homozygous adults has an abnormal constriction in the mid-sagital plane or, more rarely, several constrictions between more lateral adjacent glomeruli on both sides of the brain. No other gross structural defects are apparent in the adult brain of these animals.