Mental chronometry

Mental chronometry is the use of response time in perceptual-motor tasks to infer the content, duration, and temporal sequencing of cognitive operations. Mental chronometry is one of the core paradigms of experimental and cognitive psychology, and has found application in various disciplines including cognitive psychophysiology/cognitive neuroscience and behavioral neuroscience to elucidate mechanisms underlying cognitive processing.

History: Donders' experiment
Psychologists have developed and refined mental chronometry for over the past 100 years. Seminal early studies in reaction time were conducted by Franciscus Donders (1969).

Donders devised a subtraction method to analyze cognitive activity into separate stages, each of which requires some fairly constant time to complete. The method involved three tasks:
 * 1) A simple reaction time task. For example, you are seated in front of a panel that contains a light bulb and a response button. When the light comes on, you must press the button. An online version of this test is available here.
 * 2) A discrimination reaction time task. For example, you are seated in front of a panel with two light bulbs and one response button. When a prespecified target light (e.g., the one on the left) is illuminated, you must press the button, but not if the one on the right is illuminated.
 * 3) A choice reaction time task. For example, you are seated in front of two light bulbs, each with their own button. You must press the button corresponding to the illuminated light.

Donders then predicted the kinds of processes that might be involved in each task:
 * 1) A simple reaction time task would require perception and motor stages - the time to perceive the light and then execute the response.
 * 2) A discrimination reaction time task requires the above + a perceptual discrimination stage.
 * 3) A choice reaction time task requires all of the above + a response selection stage.

As expected, simple tasks take the shortest amount of time, followed by discrimination tasks, with choice tasks taking the longest amount of time. Donders calculated the time required for each stage by using a subtraction technique:
 * 1) Perception and motor time = time required for simple task
 * 2) 'Perceptual discrimination time'' = time for discrimination task - simple task
 * 3) Response selection time = time for choice task - discrimination task.

This method provides a way to investigate the cognitive processes underlying simple perceptual-motor tasks, and formed the basis of subsequent developments, as discussed in the next section.

Posner’s letter matching studies
Posner (1978) used a series of letter-matching studies to measure the mental processing time of several tasks associated with recognition of a pair of letters. The simplest task was the physical match task, in which subjects were shown a pair of letters and had to identify whether the two letters were physically identical or not. The next task was the name match task where subjects had to identify whether two letters had the same name. The task involving the most cognitive processes was the rule match task in which subjects had to determine whether the two letters presented both were vowels or not vowels. The physical match task was the most simple because mentally subjects had to encode the letters, compare them to each other, and make a decision. When doing the name match task subjects were forced to add a cognitive step before making a decision. They had to search memory for the names of the letters, and then compare those before deciding. In the rule based task they had to also categorize the letters as either vowels or consonants before making their choice. The time taken to perform the rule match task was longer than the name match task which was longer than the physical match task. Using the subtraction method experimenters were able to determine the approximate amount of time that it took for subjects to perform each of the cognitive processes associated with each of these tasks.

Sternberg’s memory-scanning task
Sternberg (1966) devised an experiment wherein subjects were told to remember a set of unique digits in short-term memory. Subjects were then given a probe stimulus in the form of a digit from 0-9. The subject then answered as quickly as possible whether the probe was in the previous set of digits or not. The size of the initial set of digits was the independent variable and the reaction time of the subject was the dependent variable. The idea is that as the size of the set of digits increases the number of processes that need to be completed before a decision can be made increases as well. So if the subject has 4 items in short-term memory (STM), then after encoding the information obtained from the probe stimulus the subject will need to compare the probe to each of the 4 items in memory and then make a decision. If there were only 2 items in the initial set of digits then the number of processes would be reduced by 2. The data from this study found that for each additional item added to the set of digits that the subject had in STM about 38 milliseconds were added to the response time of the subject. This finding supported the idea that a subject did a serial exhaustive search through memory rather than a serial self-terminating search. Sternberg (1969) developed a much-improved method for dividing reaction time into successive or serial stages, called the additive factor method.

Shepard and Metzler’s mental rotation task
Shepard and Metzler (1971) presented a pair of three-dimensional shapes that were identical or mirror-image versions of one another. Reaction time to determine whether they were identical or not was a linear function of the angular difference between their orientation, whether in the picture plane or in depth. They concluded that the observers performed a constant-rate mental rotation to align the two objects so they could be compared. Cooper and Shepard (1973) presented a letter or digit that was either normal or mirror-reversed, and presented either upright or at angles of rotation in units of 60 degrees. The subject had to identify which type of stimulus it was: normal or mirror-revsersed. Response time increased roughly linearly as the orientation of the letter deviated from upright (0 degrees) to inverted (180 degrees), and then decreases again until it reaches 360 degrees. The authors concluded that the subjects mentally rotate the image the shortest distance to upright, and then judge whether it is normal or mirror-reversed.

Sentence-picture verification
Mental chronometry has been a useful tool in identifying some of the processes associated with understanding a sentence. This type of research typically revolves around the differences in processing 4 types of sentences: true affirmative (TA), false affirmative (FA), false negative (FN), and true negative (TN). A picture can be presented with an associated sentence that falls into one of these 4 categories. The subject then decides if the sentence matches the picture or does not. The type of sentence determines how many processes need to be performed before a decision can be made. According to the data from Clark and Chase (1972) and Just and Carpenter (1971), the TA sentences are the simplest and take the least time, then FA, FN, and TN sentences.

Mental chronometry and models of memory
Hierarchical network models of memory were largely discarded due to some findings related to mental chronometry. The TLC model proposed by Collins and Quillian (1969) had a hierarchical structure indicating that recall speed in memory should be based on the number of levels in memory traversed in order to find the necessary information. But the experimental results did not agree with this model. For example, a subject will reliably answer that a robin is a bird more quickly than he will answer that an ostrich is a bird despite these questions accessing the same two levels in memory. This led to the development of spreading activation models of memory (e.g., Collins & Loftus, 1975), wherein links in memory are not organized hierarchically but by importance instead.

Application of mental chronometry in biological psychology/cognitive neuroscience


With the advent of functional neuroimaging techniques, notably PET and fMRI, psychologists started to modify their mental chronometry paradigms for functional imaging (Posner, 2005). Although psycho(physio)logists have been using electroencephalographic measurements for decades before the conception of PET and fMRI, the images obtained with PET have attracted great interest from other branches of neuroscience, increasingly popularizing mental chronometry among a more elaborate breed of scientists in recent years. The way that mental chronometry is utilized is by performing tasks based on reaction time which measures through neuroimaging the parts of the brain which are involved in the cognitive processes. Much research is being done now using mental chronometry and connecting it with cognitive studies however, there was extensive research being conducted in the past.

In the 1950’s, the use of a micro electrode recording of single neurons in anaesthetized monkeys allowed research to look at physiological process in the brain and supported this idea that people encode information serially.

In the 1960s, these methods were used extensively in humans: researchers recorded the electrical potentials in human brain using scalp electrodes while a reaction tasks was being conducted using digital computers. What they found was that there was a connection between the observed electrical potentials with motor and sensory stages for information processing. For example, researchers found in the recorded scalp potentials that the frontal cortex was being activated in association with motor activity. These finding can be connected to Donders’ idea of the subtractive method of the sensory and motor stages involved in reaction tasks. Then, with the invention of functional magnetic resonance imaging (fMRI), techniques were used to measure activity through electrical event-related potentials in a study when subjects were asked to identify if a digit that was presented was above or below five. According to Sternberg’s additive theory, each of the stages involved in performing this task includes: encoding, comparing against the stored representation for five, selecting a response, and then checking for error in the response. This fMRI image presents the specific locations where these stages are occurring in the brain while performing this simple mental chronometry task.

In the 1980s, neuroimaging experiments allowed researchers to detect the activity in localized brain areas by injecting radionuclides and using positron emission tomography (PET) to detect them. Also, fMRI was used which have detected the precise brain areas that are active during mental chronometry tasks. Many studies have shown that there is a small number of brain areas which are widely spread out which are involved in performing these cognitive tasks.