VISUAL MODULATION OF AIR RIGHTING BY RATS INVOLVES CALCULATION OF TIME-TO-IMPACT, BUT DOES NOT REQUIRE THE DETECTION OF THE LOOMING STIMULUS OF THE APPROACHING GROUND

Rats do not visually trigger righting when falling supine in the air. They can, however, use vision to modulate the time of onset of air rig hting depending upon the height from the ground from which they are dr opped. That is, the shorter the height, the quicker they begin to righ t. The visual cortex has been shown not to be necessary for such modul ation; however, such modulation is absent if the superior colliculus i s damaged. It is known that the superior colliculus has cells that res pond to looming stimuli, and this could be the mechanism for modulatio n during air righting. In this study, 3 experiments were conducted to test this possibility. The evidence from all 3 suggests that something other than detecting a looming stimulus (i.e., the oncoming ground) i s involved in the rats' determination of when to initiate righting. Ex pt. 1 showed that the ability to modulate the onset of air righting vi sually is not mature until adulthood (>80 days). Yet young rats do res pond to looming stimuli. Expt. 2 showed that the ability to modulate t he onset of air righting requires both eyes. One eye should be suffici ent to detect a looming stimulus. Expt. 3 showed that the rats require visual information prior to being dropped, not after, in order to mod ulate the onset of air righting. If the looming stimulus were the trig gering stimulus, then this would be detected after, not before, being dropped. These findings suggest that the rats' ability to calculate th e time-to-impact when falling involves a more complex calculation than simply detecting the presence of a looming stimulus.