Stabell, B. Transition from rod to cone vision. I. Simultaneous contrast.Scand. J. Psychol., 1969,10, 61–64.—Above the specific threshold, color quality depended on the test filter, while at lower intensities the same color was observed irrespectively of the test filter used, confirming the assumption that colors within the photochromatic interval are triggered by rod activity. The lawful relation between rise of specific threshold and increase of rod sensitivity was not found under the condition of simultaneous contr