Abstract: An electroencephalographic apparatus for exploring a person's response to external stimuli, which includes electroencephalographic sensing apparatus for sensing brainwave signals from the person; stimulating apparatus for generating the stimuli; and processing apparatus having at least a first input operative for receiving the brainwave signals, at least a second input for monitoring the stimuli; the processing apparatus including computing apparatus operative for computing a correlation quotient of the brainwave signals and the stimuli.