Reply to S. S. Stevens

Stevens believes that judgments of sensation intensity reflect the operating characteristics of the sense organs. In a recent note, he criticized the physical correlate theory as ignoring sensory physiology. This charge is refuted. Peripheral neural processes are a complex function of stimulus intensity, while psychophysical judgments follow the simple rule: equal stimulus ratios produce equal subjective ratios. It is concluded that central nervous-system processes are responsible for the direct relation between subjective intensity and the physical correlate of sensation.