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Models of timing differ on two fundamental issues, the form of the representation and the content of learning. First, regarding the representation of time some models assume a linear encoding, others a logarithmic encoding. Second, regarding the content of learning cognitive models assume that the animal learns explicit representations of the intervals relevant to the task and that their behavior is based on a comparison of those representations, whereas associative models assume that the animal learns associations between its representations of time and responding, which then drive performance. In this paper, we show that some key empirical findings (timescale invariant psychometric curves, bisection point at the geometric mean of the trained durations in the bisection procedure, and location of the indifference point in the time-left procedure) seem to make these two issues interdependent. That is, cognitive models seem to entail a linear representation of time, and at least a certain class of associative models seem to entail a log representation of time. These interdependencies suggest new ways to compare and contrast timing models., Jeremie Jozefowiez and Armando Machado acknowledge support from the Fundacao para a Ciencia e a Tecnologia as well as from the European project COST ISCH Action TD0904 "Time in Mental activity" (www.timely-cost.eu)., info:eu-repo/semantics/publishedVersion

In the time-left procedure, a task used to study prospective timing, animals choose between two stimuli that signal different delays to reinforcement. Trials begin with one stimulus signaling C seconds to reinforcement and, at different moments since its onset, another stimulus, signaling S seconds to reinforcement, with C>S, is introduced. Optimal performance consists in choosing the stimulus signaling the shorter time to reinforcement. Animals have been found to perform in this optimal way. However, this procedure is complex and variables other than time may be responsible for the results. In two experiments with pigeons we sought to improve the time-left procedure to better isolate the effect of time in the animals' behavior. We attempted to control for two confounding variables, the asymmetry in the time markers from training to testing and the cost of switching between the two response alternatives. We conclude that in the time-left task pigeons seem indeed to regulate their behavior based on time because, with our improved procedure, they still chose the stimulus associated with the shorter time to food. However, our version of the procedure created new interpretative difficulties, strengthening the idea that the time-left procedure may be too complex to study timing., The authors would like to thank Luis Oliveira for his help in developing the present study and Jeremie Jozefowiez for comments on an earlier version of the manuscript. Work supported by the Portuguese Foundation for Science and Technology (FCT) grants SFRH/BD/43398/2008 and PTDC/PSI/65678/2006., info:eu-repo/semantics/publishedVersion

We examined if the representation of time intervals in a temporal discrimination task is based not only on their absolute but also on their relative durations. Six pigeons learned two temporal discriminations. In the first, red and green choices were correct following 2-s and 8-s samples, respectively. In the second, vertical and horizontal bar choices were correct following 4-s and 16-s samples, respectively. In a previous study [Zentall, T.R., Weaver, J.E., Clement, T.S., 2004. Pigeons group time intervals according to their relative duration. Psychon. Bull. Rev. 11, 113-117.]. tests with 4-s samples and red/green comparisons revealed a bias for red, whereas tests with 8-s samples with vertical/horizontal comparisons revealed a bias for horizontal. These results were interpreted in terms of relative encoding of sample durations. We attempted to replicate this finding but instead of testing with only 4-s or 8-s samples, we tested with several other sample durations to obtain a psychometric function. Results were inconsistent with the relative encoding hypothesis., Part of the work reported here was included in a Masters thesis submitted by the first author to the University of Minho, Portugal. Research supported by a grant from the Portuguese Foundation for Science and Technology (FCT) to the second author., info:eu-repo/semantics/publishedVersion

Pigeons were placed in a long chamber equipped with one key and feeder at each end side and one key and houselight at the middle. To obtain food the birds had to choose one side key after a short signal and the other side key after a long signal. The signals consisted of the illumination of the center key and the houselight and were initiated by a peck at the center key. The chamber had sensitive floor panels that enabled us to measure the location of the bird during the signals. In Experiment 1, after the birds learned the discrimination we reversed the assignment of keys to signals. In Experiment 2, we examined performance on two pairs of discriminations holding the same ratio. In Experiment 3, after the pigeons learned to discriminate two signals, we changed the duration of the long signal. The results showed that (a) the birds' motion during the signal was highly stereotypical, i.e. the birds moved to the short side, waited a few seconds, and then departed to, and stayed on the long side; (b) this motion pattern predicted the results of generalization tests with novel durations; (c) the mean of the times of departure from the short side approached its steady state values quicker than the standard deviation and consequently superposition of behavioral measures became stronger with training; (d) only the duration of the short signal influenced significantly the moment the birds departed from the short side: finally (e) the times of arrival at and departure from the short side were positively correlated, but the times of arrival and residence at the short side were negatively correlated., info:eu-repo/semantics/publishedVersion