Abstract
An instrument has been built to study the influence of visual adaptation on the apparent brightness of simple fields of view, using an interocular (binocular or haploscopic) technique. Using this technique the observer adjusts the intensity of some attribute (e.g. the apparent brightness) of a luminous test field, viewed by only one eye, until it matches the same attribute of a second field, seen by the other eye. Among the more important adaptation variables are the levels of the preadaptation, contrast and glare luminances viewed by the observer, but the effects of other variables, including colour, field size and observation time, can also be studied by this method. Test fields of up to 14° angular subtense and adaptation fields of up to 60° are available. The instrument can be readily adapted to study the Helmholtz-Kohlrausch effect (where more saturated colours appear brighter than those less saturated but of the same luminance), while avoiding any effects of simultaneous colour contrast. Onley has suggested that the presence of contrast fields may cause interocular interaction when simultaneous interocular apparent brightness matches are made. Some experiments with the present instrument have shown that if this interaction exists, it is probably very small.