Cognitive science



Cognitive science is usually defined as the scientific study either of mind or of intelligence (e.g. Luger 1994). Practically every introduction to cognitive science also stresses that it is highly interdisciplinary; the primary components of cognitive science include psychology, neuroscience, linguistics, philosophy, and computer science, while other components include robotics, anthropology and biology.

History
The term Cognitive Science was coined by Christopher Longuet-Higgins in his 1973 commentary on the Lighthill report, which was on the state of Artificial Intelligence research.

Approaches
There are several approaches of study in the field of cognitive science including symbolic, connectionist, and dynamic systems.


 * Symbolic - That intelligence can be explained by means of systematic, discrete instructions not unlike the way in which a computer works.
 * Connectionist - The means of explanation is by using artificial neural networks.
 * Dynamic Systems - Cognition can be explained by means of a continuous system in which everything is interrelated, like the Watt Governor.

Levels of analysis
One of the central principles in the symbolic approach to cognitive science is that (1) there are different levels of analysis (LOA) from which the brain and behavior can be studied, and (2) mental phenomena are best studied from multiple levels of analysis. These levels are usually broken into three groups, based on Marr's description of them:


 * Computational (Behavioral) level: describes the directly observable output (or behavior) of a system.
 * Algorithmic (Functional) level: describes how information is processed to produce the behavioral output.
 * Implementational (Physical) level: describes the physical substrate that the system consists of (e.g. the brain; neurons).

An analogy often used to describe LOA is to compare the brain to a computer. The physical level would consist of the computer's hardware, the behavioral level represents the computer's software, and the functional level would be the computer's operating system, which allows the software and hardware components to communicate.

A central tenet of cognitive science is that a complete understanding of the mind/brain cannot be attained by studying only a single level. For example, consider the problem of remembering a phone number and recalling it later. How does this process occur? One approach would be to study behavior through direct observation. You could present a person with a phone number, ask them to recall it after some delay, and measure their accuracy. Another approach would be to study the firings of individual neurons while a person is trying to remember the phone number. Neither of these experiments on their own would fully explain how the process of remembering a phone number works. Even if we had the technology available to map out every neuron in the brain in real-time, and we knew when each neuron was firing, we still would not know how a particular firing of neurons translates into the observed behavior. Thus, we need an understanding of how these two levels relate to each other. This can be provided by a functional level account of the process. By studying a particular phenomenon from multiple levels, we are better able to understand the processes that occur in the brain to give rise to a particular behavior.

Interdisciplinary nature
Closely related to LOA (Levels of Analysis?), cognitive science is a very interdisciplinary field and tends to view the world outside the mind much as other sciences do. Thus, it has an objective: observer-independent existence. The field is usually seen as compatible with and interdependent with the physical sciences, and uses of the scientific method, as well as simulation or modeling, often comparing the output of models with aspects of human behavior. Still, there is much disagreement about the exact relationship between cognitive science and other fields, and the inter-disciplinary nature of cognitive science is largely both unrealized and circumscribed.

Many but not all who consider themselves cognitive scientists have a functionalist view of mind/intelligence, which means that, at least in theory, they study mind and intelligence from the perspective that these attributes could perhaps (at least someday) be properly attributed not only to human beings but also to, say, other animal species, alien life forms or particularly advanced computer systems. This perspective is one of the reasons the term "cognitive science" is not exactly coextensive with neuroscience, psychology, or some combination of the two.

Cognitive science - The term
The term "cognitive" in "cognitive science" is "used for any kind of mental operation or structure that can be studied in precise terms." (Lakoff and Johnson, 1999) This conceptualization is very broad, and should not be confused with how "cognitive" is used in some traditions of analytic philosophy, where "cognitive" has to do only with formal rules and truth conditional semantics. (Nonetheless, that interpretation would bring one close to the historically dominant school of thought within cognitive science on the nature of cognition - that it is essentially symbolic, propositional, and logical.)

The earliest entries for the word "cognitive" in the OED take it to mean roughly pertaining to "to the action or process of knowing". The first entry, from 1586, shows the word was at one time used in the context of discussions of Platonic theories of knowledge. Most in cognitive science, however, presumably do not believe their field is the study of anything as certain as the knowledge sought by Plato.

Scope of cognitive science
Cognitive science is a large field, and covers a wide array of topics on cognition. However, it should be recognized that cognitive science is not equally concerned with every topic that might bear on the nature and operation of the mind or intelligence. Social and cultural factors, emotion, consciousness, animal cognition, comparative and evolutionary approaches are frequently de-emphasized or excluded outright, often based on key philosophical conflicts. Some within the cognitive science community, however, consider these to be vital topics, and advocate the importance of investigating them.

Below are some of the main topics that cognitive science is concerned with. This is not an exhaustive list, but is meant to cover the wide range of intelligent behaviors. See List of cognitive science topics for a list of various aspects of the field.

Artificial intelligence
Main article: Artificial intelligence

Artificial intelligence (AI) involves the study of cognitive phenomena in machines. One of the practical goals of AI is to implement aspects of human intelligence in computers. Computers are also widely used as a tool with which to study cognitive phenomena. Computational modeling uses simulations to study how human intelligence may be structured. (See the section on computational modeling in the Research Methods section.)

There is some debate in the field as to whether the mind is "best" viewed as a huge array of small but individually feeble elements (i.e. neurons), or as a collection of higher-level structures, such as "symbols", "schemas", "plans", and rules. The former view uses connectionism to study the mind, whereas the latter emphasizes symbolic computations. One way to view the issue is whether it is possible to accurately simulate a human brain on a computer without accurately simulating the neurons that make up the human brain.

Attention
Main article: Attention

Language processing
Main articles: Cognitive linguistics, Language, Linguistics, Psycholinguistics

The ability to learn and understand language is an extremely complex process. Language is acquired within the first few years of life, and all humans under normal circumstances are able to acquire language proficiently. Some of the driving research questions in studying how the brain processes language include: (1) To what extent is linguistic knowledge innate or learned?, (2) Why is it more difficult for adults to acquire a second-language than it is for infants to acquire their first-language?, (3) How are humans able to understand novel sentences they have never heard before?

The study of language processing ranges from the investigation of the sound patterns of speech to the meaning of words and whole sentences. Linguistics often divides the types of language processing into orthography, phonology and phonetics, syntactics, semantics, and pragmatics. Many aspects of language can be studied from each of these components and from their interaction.

The study of language processing in cognitive science is closely tied to the field of linguistics. Linguistics was traditionally studied as a part of the humanities, including studies of history, art and literature. In the last fifty years or so, more and more researchers have studied knowledge and use of language as a cognitive phenomenon, the main problems being how knowledge of language can be acquired and used, and what, precisely it consists of. Linguists have found that, while humans form sentences in ways apparently governed by very complex systems, they are remarkably unaware of the rules that govern their own speech. Thus, linguists must resort to indirect methods to determine what those rules might be. If speech is indeed governed by rules, they appear to be opaque to any conscious consideration.

Learning and development
Main articles: Learning, Developmental psychology

Learning and development are the processes by which we acquire information over time. Infants are born with little or no knowledge (depending on how knowledge is defined), yet they rapidly acquire the ability to use language, walk, and recognize people and objects. Research in learning and development aim to explain the mechanisms by which these processes might take place.

A major question in the study of cognitive development is the extent to which certain abilities are innate or learned. This is often framed in terms of the nature versus nurture debate. The nativist view emphasizes that certain features are innate to an organism and are determined by its genetic endowment. The empiricist view, on the other hand, emphasizes that certain abilities are learned from the environment. It is clear that intelligent behavior has components that are both innate and learned, but the extent to which particular behaviors are innate is a major research question. In the area of language acquisition, for example, many questions remain about whether or not a special language acquisition device is necessary to facilitate the learning of language, or if humans can learn language through more general learning processes that take advantage of the information available in the environment.

Memory
Main articles: Memory

Memory allows us to store information for later retrieval. Memory is often thought of consisting of both a long-term and short-term store. Long-term memory allows us to store information over prolonged periods (days, weeks, years). We do not yet know the practical limit of long-term memory capacity. Short-term memory allows us to store information over short time scales (seconds or minutes).

Memory is also often grouped into declarative and procedural forms. Declarative memory refers to our memory for facts and specific knowledge (e.g., Who was the first president of the U.S.?). Procedural memory allows us to remember actions and motor sequences (e.g. how to ride a bicycle).

Perception and action


Main article: Perception

Perception is the ability to take in information via the senses, and process it in some way. Vision and hearing are two dominant senses that allow us to perceive the environment. Some questions in the study of visual perception, for example, include: (1) How are we able to recognize objects?, (2) Why do we perceive a continuous visual environment, even though we only see small bits of it at any one time? One tool for studying visual perception is by looking at how people process visual illusions. The image on the right of a Necker cube is an example of a bistable percept, that is, the cube can be interpreted as being oriented in two different directions.

The study of haptic (tactile), olfactory, and gustatory stimuli also fall into the domain of perception.

Action is taken to refer to the output of a system. In humans, this is accomplished through motor responses. Spatial planning and movement, speech production, and complex motor movements are all aspects of action.

Research methods
Many different methodologies are used to study cognitive science. As the field is highly interdisciplinary, research often cuts across multiple areas of study, and draws on research methods from psychology, neuroscience, and computer science.

Behavioral experiments
In order to have a description of what constitutes intelligent behavior, one must study behavior itself. This type of research is closely tied to that in cognitive psychology and psychophysics. By measuring behavioral responses to different stimuli, one can understand something about how those stimuli are processed.


 * Reaction time. The time between the presentation of a stimulus and an appropriate response can indicate differences between two cognitive processes, and can indicate some things about their nature. For example, if in a search task the reaction times vary proportionally with the number of elements, then it is evident that this cognitive process of searching involves serial and not parallel processing.


 * Psychophysical responses. Psychophysical experiments are an old psychological technique, which have been adopted by cognitive psychology. They typically involve making judgments of some physical property, e.g. the loudness of a sound. Correlation of subjective scales between individuals can show cognitive or sensory biases as compared to actual physical measurements. Some examples include:
 * sameness judgments for colors, tones, textures, etc.
 * threshold differences for colors, tones, textures, etc.


 * Eye tracking. This methodology is used to study a variety of cognitive processes, most notably visual perception and language processing. The fixation point of the eyes is linked to an individual's focus of attention. Thus, by monitoring eye movements, we can study what information is being processed at a given time. Eye tracking allows us to study cognitive processes on extremely short time scales. Eye movements reflect online decision making during a task, and they provide us with some insight into the ways in which those decisions may be processed.

Brain imaging


Brain imaging involves analyzing activity within the brain while performing various cognitive tasks. This allows us to link behavior and brain function to help understand how information is processed. Different types of imaging techniques vary in their temporal (time-based) and spatial (location-based) resolution. Brain imaging is often used in cognitive neuroscience.


 * EEG. Electroencephalography (EEG) measures the electrical fields generated by large populations of neurons in the cortex by placing a series of electrodes on the scalp of the subject. This technique has an extremely high temporal resolution, but a relatively poor spatial resolution.


 * fMRI. fMRI measures the relative amount of oxygenated blood flowing to different parts of the brain. More oxygenated blood in a particular region is correlated with an increase in neural activity in that part of the brain. This allows us to localize particular functions within different brain regions. fMRI has moderate spatial and temporal resolution.


 * Positron emission tomography. PET uses a radioactive isotope, usually in the form of glucose, which is injected into the subject's bloodstream and taken up by the brain. By observing which areas of the brain take up the radioactive isotope, we can see which areas of the brain are more active than other areas. PET has similar spatial resolution to fMRI, but it has extremely poor temporal resolution.


 * Optical imaging. This technique uses infrared transmitters and receivers to measure the amount of light reflectance by blood near different areas of the brain. Since oxygenated and deoxygenated blood reflects light by different amounts, we can study which areas are more active (those that have more oxygenated blood). Optical imaging has moderate temporal resolution, but poor spatial resolution. It also has the advantage that it is extremely safe and can be used to study infants' brains.


 * MEG. This technique measures magnetic fields resulting from cortical activity. It is similar to EEG, except that it has improved spatial resolution and the apparatus is a helmet.

Computational modeling


Computational models are often used to simulate specific aspects of intelligence. These models can help us understand the functional organization of a particular cognitive phenomenon.


 * Connectionist/neural network models. Connectionism relies on the idea that the mind/brain is composed of simple nodes and that the power of the system comes primarily from the existence, and manner of connections between the simple nodes. Neural nets are textbook implementations of this approach. Some critics of this approach feel that while it may be true as a repetition of how the system works it does not have explanative powers, as complicated systems of connections with even simple rules are extremely complex, and often less interpretable than the system they model.


 * Symbolic models.


 * Dynamical systems.

Neurobiological methods
Research methods borrowed directly from neuroscience and neuropsychology can also help us understand aspects of intelligence. This methods allow us to understand how intelligent behavior is implemented in a physical system.


 * Single-cell recording.


 * Direct brain stimulation.


 * Animal models.


 * Lesion patients.

Key findings
Cognitive science has much to its credit. Among other accomplishments, it has given rise to models of human cognitive bias and risk perception, and has been influential in the development of behavioral finance, part of economics. It has also given rise to a new theory of the philosophy of mathematics, and many theories of artificial intelligence, persuasion and coercion. It has made its presence firmly known in philosophy of language and epistemology - a modern revival of rationalism - as well as constituting a substantial wing of modern linguistics.

Discovery of systemic human cognitive bias, usually credited to Amos Tversky and Daniel Kahneman, 1967. Basis of behavioral finance.

Assertion of equivalence of Euler's identity (basis of complex analysis in mathematics) with basic cognitive processes, George Lakoff and Rafael E. Núñez, 2000. Basis of the cognitive science of mathematics.

Notable researchers in cognitive science and related fields

 * By Respective Areas

Education

 * Berkeley's "What can I do with a major in cognitive science?"

Definitions

 * Stanford Encyclopedia of Philosophy: Cognitive Science
 * aiKnow: Cognitive Artificial Intelligence
 * MIT CogNet

List of People

 * List of leading thinkers in cognitive science