The document summarizes key concepts in psychophysical measurement including: 1) It discusses the absolute sensitivity thresholds of vision, hearing, touch, and smell - the minimum stimulus needed for detection. For example, vision can detect as few as 5-14 photons and hearing can detect vibrations less than the diameter of a hydrogen molecule. 2) It describes descriptive psychophysics which examines how thresholds change under different conditions like wavelength, adaptation over time, and stimulus size and duration. 3) It introduces analytical psychophysics which uses threshold measurements to test hypotheses about the biological mechanisms underlying sensory perception.

1. Psychophysical Measurement of Thresholds: Absolute Sensitivity CHAPTER 2, Psychophysics the Fundamentals