Either it reminds you of the past, past-oriented, how the event fits in to today, yesterday and tomorrow, time line, what it is today, present, or how it will develop, future.

The three began working in 1968 when Dr Mann and Mrs Siegler were assistants to Dr Osmond, director, at the Bureau of Research, New Jersey Neuro-Psychiatric Institute in Princeton.

Dr Osmond is currently devising ways to make empirical studies of the theory and Dr Mann is in Cambridge, Massachusetts, writing a book on the Worlds of Time.

Their take-off point was an interest in observations made by Swiss psychologist Carl Gustav Jung, who described in the 1920s the temperamental differences of four psychological types.

Jung is known as the founder of analytic psychology. Since Jung's work in 1921, however, no one had conceived of a theoretical framework that would account for the four types.

Without such a framework, there was no possibility of substantiating that people of different types experience the world very differently.

Time and space are the touchstones in the systems. Each person, after all, uses his time somehow and exists within and acts upon the space around him.

Dr Mann and company propose that certain traits are shared by persons falling in each of the four categories.