A Trichotomy: Interactions of Factors Prolonging Sequential and Concurrent Mental Processes in Stochastic Discrete Mental (PERT) Networks

Suppose the mental processes required for performing a task are partially ordered. so that some pairs of processes are sequential and some are concurrent. Then they <:an be represented in a directed acyclic network. a PERT network. Suppose the duration or each proc:ess is a nonneptive random variable. Suppose two experimental factors are available. each selectively prolonpns a dill'erent proc:ess by adding a nonnegative random variable 10 ils duration. Sternberg (\969) pointed out that if all the processes are in series. the faelors will have additive effeCtson melion time, Here we show that if the faelors affect concurrent proc:csses, the facton will have subadditive effCClS. Subadditive effects are also possible if the prolonged processes are sequential, but in a Wheatstone bridge. If the PERT network has no subnetwork homeomorphic 10 a Wheatstone bridge. then ineractions belween factors prolonpng sequen. tial processes will be nonnegative. and in praclice will often be positive. The results are illustrated. in a detailed analysis of a particular network. the Embellished Wheatstone Bridge.