The transfer functions of sensory intensity in the nervous system

Abstract

Instructions are given for testing whether the input-output relation (transfer function) of a portion of any sensory system matches the tanh log relation. This relation holds for a cell membrane whose response to stimulation is an increase in permeability which shunts the source of the membrane's voltage i.e. a “self-shunting” transducer mechanism. The tanh log relation is shown to fit data for certain mechanoreceptors, photoreceptors, postsynaptic neurons, and to fit data for the responses to light by horizontal cells and C-type S-potential sites of fish, by certain ganglion cells of the frog, and for the mammalian b-waves and x-waves. The psychophysical relation between stimulus strength and magnitude estimates of sensation is fitted by a power law relation. This relation is predicted by MacKay's model which relates physiological excitation to sensation. The model is applied to psychophysical data to infer: (a) changes of lateral inhibition from photoreceptors for changes in area illuminated, (b) changes of transmission effectiveness of the pathway from the sensation generator, “the organizer”, with adaptation state or wavelength of illumination, (c) possible forms of the transfer function between the tanh log transfer function of receptors and a “comparator” stage of the model, (d) use of the Fechnerian jnd curve together with electrophysiological data to locate in the nervous system the comparator stage for a given sensory modality, (e) application of this to crudely locate the comparator and organizer stages of the mammalian visual system, (f) generalization of the model to sensory systems having linear or power law relations between stimulus strength and neural response.