From these considerations follows a principle which is of utmost importance for all psychophysiological and neurophysiological research. The events appearing after the stimulus in the brain (or in behavior) are the result of organization preceding the behavior; they do not reflect any processing of the stimulus, nor do they indicate any processes started by the stimulus per se. Every stimulus in a way closes a system, the whole activity of which leads to the result of behavior. In addition, the perception of the stimulus is a result of the preceding organization. Thus, the perceptual process is not produced by the stimulus, but is going on before its presentation. A stimulus means the possibility of acting; there is no causal relationship between the stimulus and perception because the stimulus is only one element in the system realizing perceptual results. Every perceived change in the environment means a change of behavior, and new possibilities of realizing the results of behavior. (Järvilehto, 1998, p. 331, italics added).I get the idea the stimulus is not supposed to start anything, since the stimulus is just one element in the life of the organism-system that preceded the stimulus. But, why say that there is no processing of the stimulus? And, it looks like the argument for the view that there is no causal relationship between the stimulus and perception reflects more on some background views concerning causation than on the nature of reaction time experiments.
Järvilehto, T. (1998). The theory of the organism-environment system: I. Description of the theory. Integrative Psychological and Behavioral Science, 33(4), 321-334.