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 righting depending upon the height from the ground from which they are dropped. That is, the shorter the height, the quicker they begin to right. The visual cortex has been shown not to be necessary for such modulation; however, such modulation is absent if the superior colliculus is damaged. It is known that the superior colliculus has cells that respond to looming stimuli, and this could be the mechanism for modulation 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) is involved in the rats' determination of when to initiate righting. Expt. 1 showed that the ability to modulate the onset of air righting visually is not mature until adulthood (>80 days). Yet young rats do respond to looming stimuli. Expt. 2 showed that the ability to modulate the onset of air righting requires both eyes. One eye should be sufficient to detect a looming stimulus. Expt. 3 showed that the rats require visual information prior to being dropped, not after, in order to modulate the onset of air righting. If the looming stimulus were the triggering stimulus, then this would be detected after, not before, being dropped. These findings suggest that the rats' ability to calculate the time-to-impact when falling involves a more complex calculation than simply detecting the presence of a looming stimulus.