Time left: linear versus logarithmic subjective time.

In two experiments, subjects were given a choice between a standard fixed interval to reinforcement and the time left to reinforcement in an elapsing comparison interval. In Experiment 1, rats were trained to respond on a comparison 60-sec fixed-interval schedule on one lever and a standard 30-sec fixed-interval schedule on a second lever. Then combined trials were given that began with the entry of the comparison 60-sec lever, followed by the standard 30-sec lever after 15, 30, or 45 sec. Rats preferred to respond on the standard lever when it entered early (at 15 sec), they preferred to respond on the comparison lever when the standard entered late (at 45 sec), and they were approximately indifferent between the two levers when the standard entered halfway through the comparison interval so that the remaining time to food was equal on both levers. In Experiment 2, pigeons were trained to choose between the time left to food in an elapsing comparison interval (C sec long) and a standard fixed interval one half as long (S = C/2) in a concurrent-chains paradigm. Birds came to choose the standard early and the comparison late in the trial interval. The indifference point was linearly related to the midpoint of the elapsing C interval at a variety of S,C pairs. The results of both experiments are consistent with a Scalar Timing theory in which subjective time is linear in real time and memory variance is scalar, and they are inconsistent with a logarithmic time scale.