The location and interpretation of the bisection point

In atemporal bisectiontask with humans, the observer is required to decide whether a probe duration ( t ) is more similar to the short referent (S), an R S response, or to the long referent (L), an R L response. Temporal bisection yields a psychometric function relating the proportion of long responses, P(R L ), to probe duration t . The value of t at which R S and R L occur with equal frequency, P(RL) = .5, is referred to as the bisection point, T 1/2 . Bisection models usually interpret T 1/2 as identifying the value of t that is equally confusable with S and L, but they differ in their predictions for the location of T 1/2 . The present paper presents new data relevant to the location and interpretation of T 1/2 . The data indicate that the empirical values usually are biased, the biases being influenced by duration range, L:S ratio, and probe spacing. Moreover, the biases often are not consistent across observers. It is concluded that empirical values of T 1/2 should not be interpreted as indicating the value of t that is equally confusable with S and L.