Dominatormodulator Theory

See GRANIT'S COLOR VISION THEORY.

DONDERS' LAW AND DONDERS' REACTION-TIME TECHNIQUES. The Dutch physiologist/ophthalmologist Franciscus Cornells Donders (1818-1889) formulated this principle of visual fixation in 1846, according to which every position of the lines of regard in relation to the head corresponds to a definite, invariable angle of torsion of the eyes, regardless of the path by which that position has been reached. Another version of Donders' law states that the position of the eyes in looking at an object is independent of the movement of the eyes to that position; regardless of previous fixation points, every point on the line corresponds to a definite, invariable angle of the eyes, resulting in the fixation point being focused on the retina's fovea. Aided, in part, by Hermann von Helm-holtz's invention of the ophthalmoscope in 1850, Donders established himself as a specialist in diseases of the eye, setting up a poly-clinic for eye diseases at Utrecht University. Donders improved the efficiency of spectacles through the introduction of prismatic and cylindrical lenses, and wrote extensively on eye physiology. Donders is most remembered for his studies on reaction time (RT); that is, the minimum time between the presentation of a stimulus and the participant's response to it; e.g., central RT is the fraction of RT that remains after subtracting the time taken up by the passage of a nerve impulse from the sensory receptor to the brain and for another nerve impulse from the brain to the muscle; and the subtraction method refers to any of several methods for measuring the time it takes for particular psychological processes to occur. Donders studied three kinds of RT tasks: (1) simple RT - the minimum lag between a single simple stimulus, such as a tone or light, and the participant's making of a single simple response, such as pressing a button; (2) discrimination RT - there are two distinctive stimuli and the participant is asked to respond to only one of them and refrain from making a response to the other; and (3) choice RT - an extension of simple RT where the participant is confronted with two or more stimuli and two or more corresponding responses. By subtracting the time it took participants to carry out task (2) from the time it took to carry out task (3), Donders obtained an estimate of how long it took to make a choice; and by subtracting task (1) time from task (2) time, he obtained an estimate of the individual's discrimination time. In view of the originality and ingenuity of this first attempt to measure the speed of higher mental processes, it is astonishing to see the small amount of data upon which Donders based his judgments (30 trials or less with some of his participants). However, the validity of the method of subtraction has never been fully accepted by most investigators. Nevertheless, Donders' work is important for several reasons: he showed that some of the variability of results is not due to simple differences in speed of conduction but to central processes; he laid down the foundation for the analysis of the time relations of mental processes; and he found that the RT for the different senses show characteristic differences (cf., the general theory of human reaction time - is a "non-stage" theory, and posits that the strength of the excitatory tendency leading to response evocation grows continuously as a function of the time since stimulus onset; a response occurs when this strength reaches the value of a decision criterion that is normally distributed over trials). See also HICK'S LAW. REFERENCES

Donders, F. C. (1869). Die schnelligkeit psychischer processe. Archiv fur Anatomie und Physiologie, 6, 657681.

Donders (1818-1889) and the timing of mental operations. Psychological Reports, 26, 563-569. Teichner, W., & Krebs, M. (1972). Laws of the simple visual reaction time. Psychological Review, 79, 344-358. Grice, G. R., Nullmeyer, R., & Spiker, V. A. (1982). Human reaction time: Toward a general theory. Journal of Experimental Psychology: General, 111, 135-153.

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