As mentioned above, Wundt did use Donders' experiment with the subtraction method, but preferred to do it by means of the Hipp chronoscope rather than the chronograph when he set about his reaction-time studies at Leipzig. Not only did he employ a technical change, Wundt acted on a different concept as well. He believed that a stricter definition between choice and discrimination was vital.
Donders' experiment According to one historian, Donders' experiments relied on "the assumption that each part of the reaction (sensation, perception, discrimination, choice, reaction movement) took a specific amount of time." Speech sounds were the stimulus and the reactions, recorded on a chronograph that was made up of a kymograph, or moving drum, with a tuning fork that marked the drum with the regular vibrations. In this method the differences of the time measurements would be small. The first, or "a" reaction was the simple response to the stimulus; the "b" reaction was that involved with discrimination of the sensory functions, followed by motor selection in telling the researcher what choice had been made; and the "c" reaction held to the discriminatory function but not the motor.
Only five syllables— possible examples would be "ka, ke, ki, ko, ku,"—with particular choices of one of those syllables would comprise a particular reaction. In the case of the simple reaction, both the stimulus and response was "ki;" for the "b" reaction, the stimulus was any of the five syllables with the respondent giving back that same syllable used in the stimulus; in the "c" reaction, the stimulus was any of the five syllables but the respondent was told only to react if hearing the sound of "ki." The last choice indicated that the response involved sensory discrimination but neither motor selection nor choice.
The average reaction time of the results were:
• "a" reaction: 197 milliseconds
• "b" reaction: 285 milliseconds
• "c" reaction: 243 milliseconds
Wundt liked such quantitative results when examining mental processes. Buthe decided that the Donders experiment needed an adjustment. He added a "d" reaction—discrimination without choice. What he was actually proposing here was a true psychological experiment. It was a thought experiment with no external measure as to when such a recognition would occur. Wundt would define a whole new way of experimental psychology with this. His techniques were those of self-observation, inner observation, and inner experience. Wundt held to a model for mental reaction that had five parts.
The five parts were:
• sensation, the movement of the nerve impulse from the sense organ into the brain
• perception, the entry of the signal into the field of consciousness (Blickfeld des Bewuatseins)
• apperception, the entry of the signal into the focus of attention (Blickpunkt des Aufmerksamkeits)
• act of will, in which the appropriate response signal is released in the brain
• response movement, or more precisely, the movement of the response signal from the brain to where it initiates muscular movement
Steps one and five, Wundt suggested, were purely psychological. The three middle steps were psychosocial because they had both a physiological and a psychic side. All five steps might be contained in a mental reaction. While the middle steps could not be measured, or timed separately, using the subtraction method would provide estimates of the times for apperception, and for an act of will, termed "discrimination time" and "choice time," respectively. For such experimentation, the subjects involved had to be trained in the self-observation that Wundt required so that they could properly report these psychic events.
Wundt's first doctoral students conducted experiments using this method. They followed the discrimination reaction time as it was laid out in his theory. One of the studies that used the visual stimuli had respondents press a key when they perceived a flash of light. Another reaction, the "d" reaction, provided two different images that were suddenly illuminated in front of the subject: either a white circle on black background, or a black circle on white background. As soon as the subject determined what was displayed, he would press a key. The first illumination triggered the Hip chronoscope to run, and pressing the key stopped the dial. The time that elapsed was given as the time of reaction. It is essential to note that Wundt carried out these experiments with his doctoral students Max Friedrich and Ernst Tischer. One acted as the subject, another initiated the reaction, and the third recorded the time. They took turns in different roles. Wundt utilized this model that was representative of the method he preferred to use: a subject, an experimenter, and an observer. The continued this particular experiment until they received an extremely short average time. It turned out to be similar to the result found by Donders: a range of 132 milliseconds (ms) to 226 ms. The "recognition" time added approximately 50 ms, which was Friedrich's average, to 79 ms, which was Wundt's. Using four different colors, the recognition time increased—Tischer's average was 73 ms and Friedrich's was 157 ms.
The results for the first experiment can be summarized as:
• simple reaction: 132-226 ms
• discrimination, two stimuli: 50-79 ms longer
• discrimination, four stimuli: 73-157 ms longer
The results for the second experiment can be summarized as:
• reaction with discrimination, but no choice:
• simple choice—152-184 ms longer
• multiple choice—188-331 ms longer
Wundt's experimental lab hosted hundreds of experiments utilizing various methods. Even from the initial experiments of the first doctoral students, problems had already arisen with some of Wundt's early theories. Tischer's dissertation on the discrimination of sounds, for instance, posed the already recognized situation that auditory stimulus involved a much shorter reaction time than visual. At times, the discrimination time appeared to be zero, with the time necessary to react to a sound stimulus the same as the time necessary to react when the stimulus was "recognized." Kraepelin revealed in his article, also in the first volume of Philosophische Studien, that discrimination time was particularly unreliable when the subject was influenced by drugs or alcohol. The American student Cattell, who had once been a devoted follower of Wundt, initially brought many improvements to the theory in his reaction-time experiments, only to abandon the pursuit later. His measurements lessened reaction times to such a degree that he was having a hard time keeping enough slack time to distinguish accurate discrimination time. Another student, Gustav Berger, shared the distrust of the "d" reaction, deciding that there was no definitive method for determining false reactions or to say with certainty that an apperception has occurred.
Wundt's reaction-time experiments were met with great interest in the first decade of his lab. By the end of the second decade, however, that interest had begun to wane and the experiments were rare. The new trends started focusing on emotions, and behavior theorists began to multiply. But by 1905, as was evident by the publications in his second journal (then known as the Psychologische Studien), the reaction-time studies had become prominent again. Some of them featured the sensory reaction that used the subtraction method and incorporated Wundt's theory of emotions. As previously noted, Wundt's assistant at Leipzig, Wilhelm Wirth played a key role in bringing reaction-time studies back into focus.
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