CHANGING SENSITIVITY TO DURATION IN HUMAN SCALAR TIMING - AN EXPERIMENT, A REVIEW, AND SOME POSSIBLE EXPLANATIONS

Evidence from a number of studies of human timing, using temporal gene ralization and bisection tasks, suggests more sensitive behavioural ad justment to presented durations under conditions in which the timing t ask demands discriminations between more closely spaced stimuli. An ex periment using temporal generalization demonstrated this effect, as di scrimination between a 600-msec standard duration and non-standard sti muli both shorter and longer than 600 msec was better when non-standar d stimuli were more closely spaced around 600 msec. A review showed si milar effects in other temporal generalization tasks and in a number o f bisection studies, where time discrimination improved as the ratio o f the long and short standards on the bisection task decreased. A stan dard model of human temporal generalization explained the experimental data in terms of a decrease in the response threshold under more diff icult conditions, rather than changes in the representation of the sta ndard duration. On the other hand, data from bisection could be modell ed by assuming the contrary; that representations of the short and lon g standards of the task were more precise under the more difficult con ditions. Explanations of some of these effects in terms of attention t o duration and/or arousal-induced changes in the speed of an internal clock were discussed.