[M]oment utility is measured by collecting introspective reports, but this […] is not necessary. Appropriately validated physiological measures of moment utility could be used instead, and may have important advantages. The most promising physiological indicator of momentary affect is the prefrontal cortical asymmetry in the electroencephalogram (EEG), which has been extensively validated by Davidson and his team as a measure of the balance of positive and negative feelings, and of the relative strength of tendencies toward approach or avoidance. A portable measuring instrument is not yet available, but is technically feasible. When success is achieved, Davidson’s technique will be a candidate for a continuous and non-intrusive indicator of moment utility.

Daniel Kahneman and Jason Riis, ‘Living, and Thinking about it: Two Perspectives on Life’, in Felicia A. Huppert, Nick Baylis and Barry Keverne (eds.), The Science of Well-Being, Oxford, 2005, p. 292