Search

The time-left procedure was designed to evaluate the psychophysical function for time. Although previous results indicated a linear relationship, it is not clear what role the observed bias toward the time-left option plays in this procedure and there are no reports of how variability changes with predicted indifference. The purposes of this experiment were to reduce bias experimentally, and to contrast the difference limen (a measure of variability around indifference) with predictions from scalar expectancy theory (linear timing) and behavioral economic model (logarithmic timing). A control group of 6 rats performed the original time-left procedure with C = 60 s and S = 5, 10,…, 50, 55 s, whereas a no-bias group of 6 rats performed the same conditions in a modified time-left procedure in which only a single response per choice trial was allowed. Results showed that bias was reduced for the no-bias group, observed indifference grew linearly with predicted indifference for both groups, and difference limen and Weber ratios decreased as expected indifference increased for the control group, which is consistent with linear timing, whereas for the no-bias group they remained constant, consistent with logarithmic timing. Therefore, the time-left procedure generates results consistent with logarithmic perceived time once bias is experimentally reduced. [ABSTRACT FROM AUTHOR]

Abstract: 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. This article is part of a Special Issue entitled: SQAB 2012. [Copyright &y& Elsevier]

Abstract: This study examined two possible psychophysical time scales, a logarithmic representation of time with constant variability and a linear representation of time with scalar variability. Twenty-four rats were tested on a modified temporal bisection procedure in which multiple responses could occur in a 10-s time window after the termination of a stimulus. The number of “long” or “short” responses was used as a measure of the rats’ certainty of the duration of the presented interval. Data were analyzed with signal detection theory, and straight lines were fit to the zROC curves with the assumptions of a logarithmic representation of time with constant variability and a linear representation of time with scalar variability. The logarithmic representation of time with constant variability provided a better fit to the data than the linear representation of time with scalar variability. [Copyright &y& Elsevier]