Signal intensity and duration estimation in rats

Rats were trained on a short (2-second) versus long (10-second) duration discrimination. The duration of an overhead light signaled which of two lever-press responses, left or right, would produce food reinforcement. After the rats had acquired the discrimination, probe tests were presented in which the light varied in intensity (bright or dim) and duration (values between 2 and 10 seconds). The results indicated that rats judged a bright light to be longer than a dim light of equal duration. Signal intensity has been shown to affect timing in humans and pigeons. The present results therefore extend the comparative generality of the effect to include rats as well.