LI'MEN (Lat., threshold). A metaphorical expression introduced into psychology by llerbart. The ideal boundary or limit, which ideas or representations may he said to cross on becom ing conscious. was termed by him the of eon scion sae ss! The word was then transferred by Fechner to psychophysics, where it is el11 ployed in two principal connections.. ll The 'feet of a stimulus upon the organism may. for various reasons, lie so slight as to produce no change in consciousness. _\ sound may be too faint, a point of light too small. a scent too weak, to arouse the corresponding sensation: or, on the affective side, an occurrence in the outside world may be of so little importance to us that we take it indifferently, are not 'affected' by it whether for pleasure or for unpleasantness. All stimuli of this kind are called subliminal. On the other hand, stimuli of a certain intensity or duration or extent, and occurrences of a certain 'importance, never fail, under ordinary circum stances, to evoke a conscious response; such stimuli are called supraliminal. Between the two lies the stimulus which is jii,4 able, in a given ease, to arouse a sensation or set up an affection: this just notieeable stimulus is called stint/tills /inten. In the sphere of sensation the limen may be intensive, extensive, qualitative. or temporal. We may seek to determine, e.g. the least intensity of pressure that will excite a sen sation itt the cutaneous pressure-organs, or the least intensity of that can still he heard; the smallest extension of pressure or of light that is able, under constant conditions of dura tion and intensity, to produce sensation; the least number of ai•-vilirations that can arouse the tonal quality to which their period corre sponds; the least duration of a given color or temperature that can evoke its appropriate SVII loat ion. In every case the lin•n is the just
sensible minimum of stimulation. The affective !Miens, owing in part to difficulties of experi mentation, hut chiefly to the dependence of the 'affective reaction upon the whole contents of consciousness, have IBA been worked out ( 2) What holds of stimuli holds also of differences between stimuli. Two colors may he so nearly 'alike as to 110 sensed identically; the stimulus difference is subliminal. or, they may be so dif ferent as, normally, to be sensed differently; the stimulus difference is supraliminal. t Ween the two lies a color differenee that, in the given case, is just noticeable; such a difference is called the difference limen. The ascertainment of this value is of extreme importance in psycho physics; its absolute or relative constancy de termines the absolute or relative eonstaney of the sensible discrimination. (See DISCRIMINA