Study and measurement of thought

• TYPE OF PSYCHOLOGY: Cognition

The study of thought is probably as old as thought itself. Although the measurement of thought did not originate in psychology, cognitive psychology is primarily dedicated to the study and measurement of thought processes.

Introduction

Cognitive psychologists study many processes that are basic to human nature and everyday life. Mental processes are central to who people are, what they do, and how they survive. In cognitive psychology, the study of thought necessitates its measurement. For example, much effort has been put forth in cognitive psychology to study how people understand and process information in their environment. One popular approach is to use the idea of a human information-processing system analogous to a computer. Computers are information-processing devices that use very specific instructions to achieve tasks. A computer receives input, performs certain internal operations on the data (including memory operations), and outputs certain results. Cognitive psychologists often use the information-processing metaphor in describing human operations. People must “input” information from the environment; this process includes sensory and perceptual systems, the recognition of certain common patterns of information, and attention processes.

Once this information has entered the “system,” a vast number of operations can be performed. Much of the work by cognitive psychologists has centered on the storage of information during this process—that is, on memory. While memory processes have been of interest since ancient times, it was not until the 1880s that scientists, notably Hermann Ebbinghaus, first systematically and scientifically studied memory. Scientists studying memory in contemporary times talk about concepts such as short-term and long-term memory, as well as about the distinction between episodic and semantic memory systems. The function of memory is essential to human thought and, ultimately, to the measurement of thought.

In terms of measuring what happens to incoming information, more than memory storage occurs, people manipulate these data. They make decisions based on the information available, and they have capabilities (often referred to as higher mental processes) that, in many ways, differentiate humans from other animals. Some of the functions commonly studied and measured include reasoning, problem-solving, logic, decision-making, and language development and use. The information-processing analogy is completed with the “output” of information. When a person is asked a question, the response is the output; it is based on the information stored in memory, whether those items be personal experiences, knowledge gained from books, or awareness of social customs. People do these things so effortlessly, day in and day out, that it is difficult to stop, appreciate, and comprehend how thoughts work. Psychologists have pondered these questions for many years and are only beginning to discover the answers.

Measuring Thoughts

Some of the earliest systematic studies of thought and the accompanying desire to measure it came from astronomy, not psychology or philosophy. From this beginning, Dutch physiologist Frans C. Donders set out specifically to measure a sequence of mental processes—thought—in the middle of the nineteenth century. His technique was simple yet elegant in its ability to measure how much time mental processes consume; the procedure developed by Donders is typically referred to as the subtraction technique.

The subtraction technique begins with the timing and measurement of a very basic task. For example, a person might be asked to press a button after hearing a tone. Donders realized that it was fairly easy to time accurately how long subjects took to perform this task. He believed that two cognitive (thought) processes would be operating: perception of the tone and the motor response of pressing the button. Once the time of this simple task was known, Donders would make the task more difficult. If a discrimination task were added, he believed, the time taken to complete the task would increase compared to the basic perception-motor response sequence. In this discrimination task, for example, Donders might tell a person to press the button only after hearing a high-pitched sound. That person is now faced with an added demand—to make a decision about pitch. Donders believed that with this discrimination stage, the processing of the information would require more mental effort and more time; he was right. More importantly, Donders could now measure the amount of extra thought required for the decision by subtracting the simple-task time from the discrimination-task time. In a general sense, Donders had a method for measuring thought.

Donders also had the ability to measure and manipulate specific components of the thought process. He even added another component to the sequence of tasks, what he called choice time. For example, the task could be changed so that for a high tone, the subject should press the right button, and for a low tone, press the left button. By subtracting the discrimination time from this new choice time, he could estimate how long the added choice contributed to the overall thought process. By means of these ingenious methods, Donders inspired generations of cognitive psychologists to study thought in terms of the time it takes to think.

Ebbinghaus on Learning and Forgetting

The first recognized work done in psychology on the measurement of thought processes was Ebbinghaus’s work on memory capacity and forgetting. Working independently in the 1880s in Germany, Ebbinghaus set out to study memory processes, particularly the nature of forgetting. Being the first psychologist to study the issue, he had no precedent as to how to proceed, so Ebbinghaus invented his own procedures for measuring memory. To his credit, those procedures were so good that they are still commonly used. Before describing his measurement of memory, Ebbinghaus made two important decisions about methods for studying memory. First, he studied only one person’s memory—his own. He believed he would have better control over situational and contextual variables that way.

Second, Ebbinghaus decided that he could not use everyday words in his memory studies because they might have associations that would make them easier to study. For example, if one were memorizing a poem, the story and the writing style might help memory, and Ebbinghaus was interested in a pure measure of memory and forgetting. To achieve this, Ebbinghaus pioneered the use of nonsense syllables. He used three-letter combinations of consonant-vowel-consonant so that the items were pronounceable but meaningless. Nonsense syllables such as “geb,” “fak,” “jit,” “zab,” and “buh” were used.

Ebbinghaus used a vigorous schedule of testing and presented himself with many lists of nonsense syllables to be remembered at a later time. In fact, he spent five years memorizing various lists until he published his seminal work on the topic, Über das Gedächtnis: Untersuchurgen zur experimentellen Psychologie (1885; Memory: A Contribution to Experimental Psychology, 1913). He systematically measured memory by memorizing a list, letting some time pass, and testing himself on the list. He devised a numerical measurement for memory called percent savings. Percent savings was a measure of the degree of forgetting that occurred over time. For example, it might take him ten minutes to memorize a list perfectly. He would let forty-eight hours pass, then tell himself to recall the list. Forgetting would occur during that time, and only some items would be remembered. Ebbinghaus would then look at the original list and rememorize it until he knew it perfectly; this might take seven minutes or so. He always spent less time rememorizing the list. Said another way, there were some savings from the earlier experience forty-eight hours before. This percent savings was his measure of memory. The higher the percentage of savings, the more items remembered (or the fewer forgotten), and Ebbinghaus could remember the list in less time.

Ebbinghaus then varied the time between original list learning and later list recall. He found that percent savings drops over time; that is, the longer one waits to remember something, the less one saves from the prior experience, so the more time he had to spend rememorizing the list. Ebbinghaus found fairly good percent savings two or nine hours later, but percent savings dropped dramatically after two or three days. Plotted on a graph, this relationship looks like a downward-sloping curve, and it is called the Ebbinghaus forgetting curve. Simply stated, it means that as time passes, memories become poorer. Although this effect is not surprising today, Ebbinghaus was the first (in 1885) to demonstrate this phenomenon empirically.

Sternberg on Speed

Another example of the work in the area of cognitive psychology comes from the studies of Saul Sternberg in the 1960s at Bell Laboratories. Sternberg examined how additional information in memory influences the speed of mental operations in retrieving information stored in memory. Sternberg’s task was fairly simple. He presented people with a list of numbers; the list might range from one to six numbers. After the people saw this initial list, a single number (called a probe) was presented. People were asked to identify whether the probe number was on the initial list of numbers. The list might be 2, 3, 9, and 5, for example, and the probe might be 3.

Sternberg’s primary interest was in studying how the length of the initial list affected the time it took to make the required yes-or-no decision. Two possibilities typically emerge when people consider this problem. The concept called serial processing holds that the comparison of the probe to each number in the initial list takes time, so that the more items in the initial list, the longer the memory search takes. An alternative idea, parallel processing, suggests that people instantaneously scan all the items in the memory set, and the number of items in the initial list does not make a difference. Another way of saying this is that all the items are scanned at once, in parallel fashion. Sternberg found that people search their memories using the technique of serial processing. In fact, he was able to calculate precisely the amount of additional search time needed for each added item in the memory set—38 milliseconds (a millisecond is a thousandth of a second). Although the search may seem fast, even instantaneous, the more there is to think about, the more time it takes to think.

Cognitive Psychology

The study of thought, and particularly its measurement, is a relatively recent development. For centuries, the thinking processes of humans were believed to be somewhat mystical and certainly not available for scientific inquiry. Most philosophers were concerned more with the mind and its relationship to the body or the world than with how people think. The study of thought, although it was generally considered by the ancient Greek philosophers, did not merit serious attention until the emergence of the “personal equation” by astronomers and the realization that thought processes are indeed measurable and can be measured accurately and precisely.

The story of the first recorded measurements of thought begins with the royal astronomer to England, Nevil Maskelyne, and his assistant, David Kinnebrook, in 1794. Astronomers of the day were mostly concerned with stellar transits (measuring the movement of stars across the sky). Using telescopes and specialized techniques, the astronomer sought to measure the time it took for a particular star to move across a portion of the telescopic field. Using a complicated procedure that involved listening to a beating clock and viewing the sky, astronomers could measure the transit time of a star fairly accurately, to within one-tenth or two-tenths of a second. These measurements were particularly important because the clocks of that period were based on stellar transits.

Maskelyne and Kinnebrook often worked together to record the movement of the stars. While Kinnebrook had no problems during 1794, in 1795, Maskelyne began to notice that Kinnebrook’s times varied from his own by as much as one-half of a second—considered a large and important difference. By early 1796, the difference between the astronomers’ times had grown to eight-tenths of a second. This was an intolerable amount of error to Maskelyne, and he fired his assistant Kinnebrook.

About twenty years later, a German astronomer named Friedrich Bessel came across the records of these incidents and began to study the “error” in the differing astronomers’ measurements. He believed that the different measurements were attributable in part to differences between people and that this difference was not necessarily an error. He found that even the most famous and reliable astronomers of the day differed from one another by more than two-tenths of a second.

This incident between Maskelyne and Kinnebrook, and its later study by Bessel, led to some important conclusions. First, measurements in astronomy would have to consider the specific person making the measurement. Astronomers even went to the lengths of developing what became known as the personal equation. The personal equation was a verified, quantified account of how each astronomer’s thought processes worked when measuring stellar transits. In essence, the personal equation was a measurement of the thought process involved and a recognition of differences between people. Second, if astronomers differ in their particular thought processes, then many people differ in other types of thinking processes as well. Finally, and perhaps most important in the long run, this incident laid the groundwork for the idea that thought could be measured accurately and the information could be put to good use. No longer was thinking a mystical or magical process that was unacceptable for study by scientists.

It is from this historical context that the field of cognitive psychology has emerged. Cognitive psychology is chiefly concerned with the thought processes and, indeed, all the general mental processing of organisms (most often humans). The interests of a cognitive psychologist can be quite varied: learning, memory, problem-solving, reasoning, logic, decision-making, linguistics, cognitive development in children, and other topics. Each area of specialization continues to measure and examine how people think, using tasks and procedures as ingenious as those of Donders, Ebbinghaus, and Sternberg. The study and measurement of thought (or, more generally, the field of cognitive psychology) will continue to play an important and vital role. Not many questions are more basic to the study of human behavior than how people think, what processes are involved, and how researchers can scientifically study and measure these processes.

Bibliography

Anderson, John R. Cognitive Psychology and Its Implications. 7th ed., Worth Publishers, 2009.

Ashcraft, Mark H., and Gabriel A. Radvansky. Cognition. 6th ed., Pearson, 2013.

Boring, Edwin G. A History of Experimental Psychology. 2nd ed., Prentice-Hall, 1957.

Goodwin, C. James. A History of Modern Psychology. 4th ed., John Wiley & Sons, 2012.

Lachman, Roy, et al. Cognitive Psychology and Information Processing: An Introduction. Lawrence Erlbaum Associates, 1979.

Max Planck Institute for Human Cognitive and Brain Sciences. "Measurement of Thoughts During Knowledge Acquisition." ScienceDaily, 25 Mar. 2019, www.sciencedaily.com/releases/2019/03/190325110227.htm. Accessed 7 Jan. 2025.

Reisberg, Daniel, editor. The Oxford Handbook of Cognitive Psychology. Oxford University Press, 2013.