However - what does cognitive psychology actually mean? It is quite a broad term, and we could single out at least four main sub-disciplines: experimental cognitive psychology, cognitive neuropsychology, computational cognitive science and cognitive neuroscience. In this post, I will explain how these disciplines differ from each other and where the main focus of each of them lies. At first, however, I will briefly discuss how experimental psychology evolved during the XX century.
Eras of Experimental psychology
Introspection is examination of the one's own conscious thoughts and feelings - as opposed to the external observation. Generally speaking, it gives a direct access to one's mental state without any influence of other sources of knowledge. Introspection was brought into the experimental psychology by Wilhelm Wundt; although the idea existed since mid-18th century, he was the first to apply it in his experimental laboratory in Leipzig, thus making it possible for other psychologists to study and replicate his work. Wundt considered self-observation ('internal perception') as a means to measure immediate experience of human consciousness including thoughts, feelings and emotions.
Introspection gave birth to the movement of Structuralism, founded by Wundt's student Edward Titchener. Using introspection, he attempted to divide human mind into structures - just like a chemist would break chemicals down to their components. Titchener argued that any sensation has four characteristics: intensity, quality, duration and extent. He also separated them into types - such as auditory. Ideas and perceptions he considered to be formed from sensations; "ideational type" was related to the type of sensation on which an idea was based, e.g., sound or vision. Titchener believed that if the basic components of the mind could be defined and categorized that the structure of mental processes and higher thinking could be determined.
However, introspection was rejected in the beginning of the XX century by most of the psychological community, being considered unreliable and subjective. Behaviourism was the new 'big thing'.
2. 1915-1956: Behaviourist Psychology
One of the key figures associated with behaviourism was B. F. Skinner. You must have heard of the Skinner Box? If not, check out the short video below. Basing on the pigeons' (or other animals) behaviour, Skinner argued that human behaviour was guided by an external stimulus and appropriate response. Concepts linked to this idea are also operational conditioning and reinforcement (see the video). In his theory, there were no mental representations/processes involved in cognition; instead, his model could be described as: stimulus -> response -> reinforcement.
In 1948, American mathematician Shannon came about with his Information Theory. It derived from the signal processing in the WWII communications, and proposed that information was communicated by sending a signal through a set of transformations or stages. In 1950s it led to the emergence of an idea that cognition could be also viewed as a flow of information through the organism, processed by a human mind; this shift from behaviourism became known as a cognitive revolution. On September 11, 1956, a large-scale meeting of cognitivists took place at the Massachusetts Institute of Technology; this date is now considered to mark birth of cognitive psychology. Unlike behaviourism, cognitive psychology explicitly acknowledges the existence of internal mental states. It also accepts that human minds represent and process information.
Noam Chomsky's studies of language also presented a direct challenge to behaviourist ideas, since human language is combinatorial and productive and involves creativity; people can say and understand things they have never heard/said before.
So, the main assumptions of cognitive psychology are that there are internal mental processes and they can be studied scientifically. Response time is used as a means to measure them: time elapsing between some stimulus is presented to an individual and his/her reaction to it. This is based on the assumption that mental processes take time.
Cognitive Psychology: sub-disciplines
This discipline uses experiments and hypothesis testing to study the representations and processes underlying cognition. According to David Marr, one should understand any cognitive process at three levels of analysis:
a) Computational: what does a certain system do, which problems it solves and why (for example, which brain area contains the rules of arithmetic to solve 2+2 problem)
b) Algorithmic/representational: how systems do what they do and what representations and processes they use.
c) Physical: how does the system physically work; its physical substrate (which neural structures are involved etc.).
2. Cognitive neuropsychology
Cognitive neuropsychology traditionally studies developmental and accidental brain injuries and neurological illnesses in order to understand functioning of a normal brain. It accepts the idea of a functional localisation: that if a specific cognitive problem is found after an injury to a specific brain area, it is possible that this part of the brain is in some way involved.
However, cognitive neuropsychology has numerous limitations. Firstly, it is possible that the link is not that simple; functions may be much more distributed across the brain - rather than being performed by one area. Secondly, there are great individual differences, which make it quite problematic to generalise results based on a single case.
Also, often brain 'relocates' the functions which can not longer be performed by a damaged area to other parts of the brain; this is what is referred to as brain compensatory strategies. They are more frequent in patients with developmental injuries, but may occur in those with accidental damages as well - especially in younger age, when the brain is still flexible. This short video offers a great example of such a case: a child had a stroke during the pre-natal period, which led to the huge loss of white and grey matter in the language areas of her brain. However, by the age of 6 she could produce and comprehend speech like normal children.
Computational cognitive science uses computational modelling in order to symbolically represent functioning of the brain and its systems in a formal and logical way. One of such well-known models is a dual-route cascaded model of reading (Coltheart et al., 2001) which I described in one of the Psychology of Language posts here.
4. Cognitive Neuroscience
This field studies biological substrates underlying cognition, with a specific focus on neurology of mental processes. Its main question is: how does brain perform its cognitive functions? The methods used in the field are numerous, and they quickly develop. Some of them are:
a) Single unit recordings
This method allows to measure activity of a single neuron by inserting a microelectrode in the brain. When a neuron generates action potential, the electric current goes through the membrane in the axon and soma; microelectrode then records the rate of change in voltage in respect to time. The microelectrodes can be placed either within or very close to the membranes of the cells, thus recording signals either intracellularly or extracellularly.
ERP is a measured brain response to a specific sensory, cognitive or motor stimuli. Its big plus is that it is a non-invasive way of evaluating activity and functioning of the brain. It is also much cheaper than inserting microelectrodes and using fMRI and PET. However, it only produces temporal, but not spacial resolutions. In other words, it can show very precisely when brain activates - however not where it activates.
fMRI measures brain activity by detecting changes in blood flow; the idea is that blood flows to the the parts of the brain which are 'at work' during a particular cognitive activity/task. The procedure uses the change in magnetisation between oxygen-rich and oxygen-poor blood as its basic measure. Brain activation can be presented graphically by colour-coding the strength of activation across the brain or the specific region studied. The technique can localise activity to within millimetres but, using standard techniques, within a window of a few seconds.