Evidence that pigeons represent both time and number on a logarithmic scale

Pigeons were presented with trials that always began with presentation of a houselight that lasted for 1–16 s. Red and green side keys were presented immediately after the houselight went off. A peck on the red key was reinforced if the houselight duration was 8 s or shorter, and a peck on the green key was reinforced if the houselight duration was 9 s or longer. Plots of asymptotic performance as a function of houselight duration showed bow-shaped curves with higher accuracy at the ends of the scale than in the middle. Training to bisect a scale containing houselight durations of 2–32 s yielded a performance curve that superimposed on the 1–16 s curve. Both curves showed two important asymmetries around the midpoint: pigeons were more accurate at 9 and 10 s than at 7 and 8 s but were more accurate at 1–4 s than at 13–16 s. These findings closely resembled those found in a similar study of number scale bisection [Roberts, W.A., 2005. How do pigeons represent numbers? Studies of number scale bisection. Behav. Process. 69, 33–43]. Theoretical predictions from associative and confusion models showed a good match to the obtained data if it was assumed that time and number scales were logarithmic and that generalization or confusion curves were constant but not if it was assumed that scales were linear and that generalization or confusion curves were scalar.