When is an easy task difficult and vice versa? A reply to lane

Lane has argued that kantowitz and Knight incorrectly predicted an interaction between primary and secondary task difficulty for the variable-allocation model of attention. It is shown that such an interaction is indeed obtained if task-performance difficulty is defined in terms of capacity and only reasonable transformations of data are permitted. This interaction holds for any set of monotonic resource operating characteristics.     

Channels and stages in human information processing: A limited analysis of theory and methodology

This article reviews the status of the theoretical construct of capacity. Four basic questions are discussed: (1) What is capacity? (2) How is capacity measured? (3) Is capacity limited? (4) If so, where is it limited? It is claimed that empirical answers to these questions have been unsatisfactory due to theoretical and methodological issues that need be resolved. Data are presented to illustrate such difficulties. The construct of capacity has become more and more vacuous and caution is required whenever capacity is invoked to explain behavior. These problems can be overcome by careful research and well-defined models. Capacity can be a soup stone, a millstone, or a touchstone, depending upon how it is used.