by firing at a faster or slower rate according to the intensity of a stimulus, an axon can communicate quantitative information to the brain. weber noticed that the jnd is directly related to the magnitude of that stimulus (ex. two stimuli would be similar unless they differenced by a factor of. 1/40 the ratio that held mostly constant: weber fraction: reasonably constant over the middle range of most stimulus intensities (the 1/40 from example above) the ratio between a jnd and the magnitude of a stimulus; Signal detection theory: threshold: be just detected (not always an absolutely fixed value) the point at which a stimulus or change in the value of a stimulus can. Photoreceptor: a receptive cell for vision in the retina; a rod or a cone. photoreceptors respond to light and pass the information on by means of a transmitter substance to o.