Measuring Mental Chronometry: A Qualitative Study

The purpose of these three distinct methods of measuring mental chronometry is to separate the subcomponents that theoretically comprise a mental reaction RT (O'Shea & Bashore, 2012). The first method, referred to as a-method, actually originated from work done by an astronomer Aldof Hirsch (Canales 2001). Hirsch’s studies were conducted in the 1860’s and consisted of repeated exposure of a single stimulus to a subject. The subjects were simply instructed to give a fixed response when they perceived the stimulus. The assumption was that the RT, being the time from presentation to response, was a representation of the time needed for the processes associated with transmission of basic stimuli and the activation of motor information through the nervous system. This was a process that did not involve any decision making regarding the stimulus given and choice of response and due to these task restrictions, this type of stimulus-response paradigm is termed ‘simple reactions’.
The next method Donders proposed was referred to as b-method. This method included a choice reaction in addition to the simple reaction of a-method. These studies involved having subjects discriminate between two distinct stimuli, each of which having a distinct response association. Simply put, the difference between

a-method and b-method is the addition of a choice reaction to the simple reaction. The assumption here was that the measured RT from stimulus presentation to response in these tasks included the simple reactions as before, but with the addition of the times needed to discriminate between stimuli and identify the correct response.
Finally, the c-method was proposed as the third method for measuring mental chronometry. This method used a task that is now commonly referred to as the go/no-go task, and is still widely used in current research studies. The subject in this task is presented with many distinct stimuli, only one of which is to illicit a response. The assumption behind this task is that the measured RT from presentation to response, is the representation of the mental processes involved in stimulus discrimination speed. These responses lack any accompanying response selection times since the subject has only one possible response and that response was selected in advance of any stimulus presentations.
With the addition of the more complex processing requirements needed to complete the different tasks used in the three methods, there came an increase in subject RT. The subject RT for the task used in a-method, which was just responding to a single stimuli with a single response, was faster when compared with the RT for the b-method task. The b-method task included the requirement for the subjects to discriminate between two different stimuli and to give the appropriate response when needed. When an increase in RT is observed, the assumption is that the difference is the time needed to make a serial decision between the basic stimuli and response, which is independent of the time needed for the processes (sensory, motor) needed to perform a simple reaction. This process led to the subtraction method for determining the mental time needed for each cognitive action. An example of the subtraction method would be taking the RT form c-method (go/no-go task) which consists of the processing subcomponents of discrimination and physiological (simple reaction) times, and subtracting that RT from those of b-method, which consists of times associated with discrimination, response selection and physiological subcomponents. This subtraction would yield an estimate for the response selection time subcomponent independent of discrimination and physiological time components. It is also possible to differentiate between other subcomponents using the subtraction method. If the RT from a-method (simple reaction), which consists of only times associated with the physiological subcomponent, is subtracted from RT of c-method (go/no-go) which has time from both the discrimination and physiological subcomponents, this would yield an estimation of the mental time needed to complete the stimulus discrimination subcomponent of RT.
Using the combination of these three different mental chronometry measures and the subtraction method it was possible, for the first time, to separate the subcomponents of mental reaction RT. This was a critical first step in understanding the underlying theoretical assumptions behind the analysis of RT data. As is common in the history of psychology and science in general, other researchers took Donders’ methods and added their own ideas in attempt to further the understanding and usefulness of the theory of mental chronometry and RT measurements.
One such researcher who focused on improving RT protocol was the influential Wundt.

Wundt used the core ideas established by Donder and added the d-method to the existing a, b and c-methods (Wundt 1880/1969). Subjects in Wundt’s lab were asked to give the same response to multiple different stimuli with an additional instruction to first recognize (or “apperceive” as Wundt termed it) the stimulus before responding to it. The addition of this recognition task was hypothetically a way to measure pure discrimination. Wundt claimed that his d-method was a more accurate measure for stimulus discrimination than Donders’ c-method, and thus an improvement on the RT

methodology.
Another early psychologist that looked to improve upon the RT and subtraction methodology was Edumnd C. Sanford (Sanford 1888,1889). Sanford again used ideas from astronomy to formulate what he would call the ‘Personal Equation’ (Sanford 1889). In the early 19th century, astronomers used what was called the ‘eye and ear’ method to chart the transit times of identified starts as they passed through the crosshairs of a telescope. The observer was to integrate the visual information of the moving star with auditory information, which was the ticking of a clock. This method lends itself to a large amount of variability based upon the accuracy, or inaccuracy of the observer. To correct for this, Friedrich Bessel, a German astronomer, in 1822 formulated a subtraction procedure which yielded the average difference in observation times between two astronomers tracking the same stellar transit. Sanford then adapted this formula for use with mental chronometry in an attempt to decrease the variability associated with individual difference in subject RT (Sanford 1888).
Along the same line of research as Wundt’s work with RT, Sanford (1893) also ran a series of experiments using numerous variations of mild electrical stimulation to a subject’s hands to measure RT using a variation of the d-method. The subjects were instructed as to which hand was going to receive the electric stimulation, and the assumption was that the expectation by the subjects would decrease RT. A major problem with this methodology was that Sanford asked the subject after each trial to rate their reactions as either ‘good’, ‘too late’, or ‘too early’ and he only used the reactions rated as ‘good’ in the analysis. Sanford ended up with a finding that RT for the reacting hand were faster than those for the non-stimulated hand. This was the first influential use of RT with subject introspection as an element included in the methodology.
Other researchers continued on this trend of subject introspection as a part of RT (Lange 1888; Wantanabe 1894) in experiments focused on separating sensorial reaction and muscular reaction. These experimental tasks included the requirement of the subject to prepare their reactions based on either the appearance of the stimulus, which was a sensorial reaction, or the activation of movement needed for responding, which was a muscular reaction. The assumption was that the RT for sensorial reactions would be longer than muscular reactions due to the fact that a sensorial reaction would include both perception and apperceiving of the stimulus before responding, where as a muscular reaction consists of only perception of the stimulus before a response. In theory this idea makes sense, but in order for this methodology to work, it relies on the introspective reports of the subjects to determine that they are in fact keeping their response preparations separate for sensorial and muscular reactions. This a very heavy reliance on a subjective introspective measure to validate the data. When the data from these studies didn’t support the researcher’s hypothesis, the claim was that the d-method wasn’t followed properly and that the subjects were not properly following instructions (Lange 1888). This idea that introspection was needed for accurate RT data parallels with the general movement in psychology at this time that stressed the use introspection as the primary means of psychological research.