Russell T. Hurlburt pioneered the investigation of inner experience (thoughts, feelings and so on), inventing (in 1973) the beepers that launched 'thought sampling', the attempt to measure characteristics of inner experience. Despite the sophistication of his thought-sampling measurements, Hurlburt concluded, by about 1980, that science needs a better understanding of inner phenomena themselves. Therefore he developed Descriptive Experience Sampling (DES), the attempt to apprehend inner experience in high fidelity. That has led to four books: Sampling Normal and Schizophrenic Inner Experience