ACT-R (pronounced /ˌækt ˈɑr/; short for "Adaptive Control of Thought—Rational") is a
cognitive architecture A cognitive architecture refers to both a theory about the structure of the human mind and to a computational instantiation of such a theory used in the fields of artificial intelligence (AI) and computational cognitive science. The formalized mod ...
mainly developed by
John Robert Anderson and Christian Lebiere at
Carnegie Mellon University
Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania. One of its predecessors was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools; it became the Carnegie Institute of Technology ...
. Like any cognitive architecture, ACT-R aims to define the basic and irreducible cognitive and perceptual operations that enable the human mind.
In theory, each task that humans can perform should consist of a series of these discrete operations.
Most of the ACT-R's basic assumptions are also inspired by the progress of
cognitive neuroscience
Cognitive neuroscience is the scientific field that is concerned with the study of the biological processes and aspects that underlie cognition, with a specific focus on the neural connections in the brain which are involved in mental proces ...
, and ACT-R can be seen and described as a way of specifying how the brain itself is organized in a way that enables individual processing modules to produce cognition.
Inspiration
ACT-R has been inspired by the work of
Allen Newell
Allen Newell (March 19, 1927 – July 19, 1992) was a researcher in computer science and cognitive psychology at the RAND Corporation and at Carnegie Mellon University’s School of Computer Science, Tepper School of Business, and Department ...
, and especially by his lifelong championing the idea of unified theories as the only way to truly uncover the underpinnings of cognition.
In fact, Anderson usually credits Newell as the major source of influence over his own theory.
What ACT-R looks like
Like other influential cognitive architectures (including
Soar,
CLARION
Clarion may refer to:
Music
* Clarion (instrument), a type of trumpet used in the Middle Ages
* The register of a clarinet that ranges from B4 to C6
* A trumpet organ stop that usually plays an octave above unison pitch
* "Clarion" (song), a 2 ...
, and EPIC), the ACT-R theory has a computational implementation as an interpreter of a special coding language. The interpreter itself is written in
Common Lisp
Common Lisp (CL) is a dialect of the Lisp programming language, published in ANSI standard document ''ANSI INCITS 226-1994 (S20018)'' (formerly ''X3.226-1994 (R1999)''). The Common Lisp HyperSpec, a hyperlinked HTML version, has been derived fro ...
, and might be loaded into any of the Common Lisp language distributions.
This means that any researcher may download the ACT-R code from the ACT-R website, load it into a Common Lisp distribution, and gain full access to the theory in the form of the ACT-R interpreter.
Also, this enables researchers to specify models of human cognition in the form of a script in the ACT-R language. The language primitives and data-types are designed to reflect the theoretical assumptions about human cognition.
These assumptions are based on numerous facts derived from experiments in
cognitive psychology
Cognitive psychology is the scientific study of mental processes such as attention, language use, memory, perception, problem solving, creativity, and reasoning.
Cognitive psychology originated in the 1960s in a break from behaviorism, which ...
and
brain imaging
Neuroimaging is the use of quantitative (computational) techniques to study the neuroanatomy, structure and function of the central nervous system, developed as an objective way of scientifically studying the healthy human brain in a non-invasive ...
.
Like a
programming language
A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language.
The description of a programming ...
, ACT-R is a framework: for different tasks (e.g., Tower of Hanoi, memory for text or for list of words, language comprehension, communication, aircraft controlling), researchers create "models" (i.e., programs) in ACT-R.
These models reflect the modelers' assumptions about the task within the ACT-R view of cognition.
The model might then be run.
Running a model automatically produces a step-by-step simulation of human behavior which specifies each individual cognitive operation (i.e., memory encoding and retrieval, visual and auditory encoding, motor programming and execution, mental imagery manipulation).
Each step is associated with quantitative predictions of latencies and accuracies.
The model can be tested by comparing its results with the data collected in behavioral experiments.
In recent years, ACT-R has also been extended to make quantitative predictions of patterns of activation in the brain, as detected in experiments with
fMRI
Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...
.
In particular, ACT-R has been augmented to predict the shape and time-course of the
BOLD
In typography, emphasis is the strengthening of words in a text with a font in a different style from the rest of the text, to highlight them. It is the equivalent of prosody stress in speech.
Methods and use
The most common methods in W ...
response of several brain areas, including the hand and mouth areas in the
motor cortex
The motor cortex is the region of the cerebral cortex believed to be involved in the planning, control, and execution of voluntary movements.
The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately a ...
, the left
prefrontal cortex
In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, BA13, BA14, BA24, BA25, BA32, BA44, BA45, BA46, ...
, the anterior
cingulate cortex
The cingulate cortex is a part of the brain situated in the medial aspect of the cerebral cortex. The cingulate cortex includes the entire cingulate gyrus, which lies immediately above the corpus callosum, and the continuation of this in the ci ...
, and the
basal ganglia
The basal ganglia (BG), or basal nuclei, are a group of subcortical nuclei, of varied origin, in the brains of vertebrates. In humans, and some primates, there are some differences, mainly in the division of the globus pallidus into an extern ...
.
Brief outline
ACT-R's most important assumption is that human knowledge can be divided into two irreducible kinds of representations: ''
declarative'' and ''
procedural''.
Within the ACT-R code, declarative knowledge is represented in the form of ''chunks'', i.e. vector representations of individual properties, each of them accessible from a labelled slot.
Chunks are held and made accessible through ''buffers'', which are the front-end of what are ''modules'', i.e. specialized and largely independent brain structures.
There are two types of modules:
* Perceptual-motor modules, which take care of the interface with the real world (i.e., with a simulation of the real world). The most well-developed perceptual-motor modules in ACT-R are the visual and the manual modules.
* Memory modules. There are two kinds of memory modules in ACT-R:
** Declarative memory, consisting of facts such as ''Washington, D.C. is the capital of United States'', ''France is a country in Europe'', or ''2+3=5''
** Procedural memory, made of productions. Productions represent knowledge about how we do things: for instance, knowledge about how to type the letter "Q" on a keyboard, about how to drive, or about how to perform addition.
All the modules can only be accessed through their buffers. The contents of the buffers at a given moment in time represents the state of ACT-R at that moment. The only exception to this rule is the procedural module, which stores and applies procedural knowledge. It does not have an accessible buffer and is actually used to access other module's contents.
Procedural knowledge is represented in form of ''productions''. The term "production" reflects the actual implementation of ACT-R as a
production system, but, in fact, a production is mainly a formal notation to specify the information flow from cortical areas (i.e. the buffers) to the basal ganglia, and back to the cortex.
At each moment, an internal pattern matcher searches for a production that matches the current state of the buffers. Only one such production can be executed at a given moment. That production, when executed, can modify the buffers and thus change the state of the system. Thus, in ACT-R, cognition
unfolds as a succession of production firings.
The symbolic vs. connectionist debate
In the
cognitive sciences, different theories are usually ascribed to either the "
symbolic" or the "
connectionist
Connectionism refers to both an approach in the field of cognitive science that hopes to explain mind, mental phenomena using artificial neural networks (ANN) and to a wide range of techniques and algorithms using ANNs in the context of artificial ...
" approach to cognition. ACT-R clearly belongs to the "symbolic" field and is classified as such in standard textbooks and collections. Its entities (chunks and productions) are discrete and its operations are syntactical, that is, not referring to the semantic content of the representations but only to their properties that deem them appropriate to participate in the computation(s). This is seen clearly in the chunk slots and in the properties of buffer matching in productions, both of which function as standard symbolic variables.
Members of the ACT-R community, including its developers, prefer to think of ACT-R as a general framework that specifies how the brain is organized, and how its organization gives birth to what is perceived (and, in cognitive psychology, investigated) as mind, going beyond the traditional symbolic/connectionist debate. None of this, naturally, argues against the classification of ACT-R as symbolic system, because all symbolic approaches to cognition aim to describe the mind, as a product of brain function, using a certain class of entities and systems to achieve that goal.
A common misunderstanding suggests that ACT-R may not be a symbolic system because it attempts to characterize brain function. This is incorrect on two counts: First, all approaches to computational modeling of cognition, symbolic or otherwise, must in some respect characterize brain function, because the mind is brain function. And second, all such approaches, including connectionist approaches, attempt to characterize the mind at a cognitive level of description and not at the neural level, because it is only at the cognitive level at which important generalizations can be retained.
Further misunderstandings arise because of the associative character of certain ACT-R properties, such as chunks spreading activation to each other, or chunks and productions carrying quantitative properties relevant to their selection. None of these properties counter the fundamental nature of these entities as symbolic, regardless of their role in unit selection and, ultimately, in computation.
Theory vs. implementation, and Vanilla ACT-R
The importance of distinguishing between the theory itself and its implementation is usually highlighted by ACT-R developers.
In fact, much of the implementation does not reflect the theory.
For instance, the actual implementation makes use of additional 'modules' that exist only for purely computational reasons, and are not supposed to reflect anything in the brain (e.g., one computational module contains the pseudo-random number generator used to produce noisy parameters, while another holds naming routines for generating data structures accessible through variable names).
Also, the actual implementation is designed to enable researchers to modify the theory, e.g. by altering the standard parameters, or creating new modules, or partially modifying the behavior of the existing ones.
Finally, while Anderson's laboratory at
CMU maintains and releases the official ACT-R code, other alternative implementations of the theory have been made available. These alternative implementations include ''jACT-R'' (written in
Java
Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...
by Anthony M. Harrison at the
Naval Research Laboratory
The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. It was founded in 1923 and conducts basic scientific research, applied research, technological ...
) and ''Python ACT-R'' (written in
Python
Python may refer to:
Snakes
* Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia
** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia
* Python (mythology), a mythical serpent
Computing
* Python (pro ...
by Terrence C. Stewart and Robert L. West at
Carleton University
Carleton University is an English-language public research university in Ottawa, Ontario, Canada. Founded in 1942 as Carleton College, the institution originally operated as a private, non-denominational evening college to serve returning World ...
, Canada).
Similarly, ACT-RN (now discontinued) was a full-fledged neural implementation of the 1993 version of the theory.
[Lebiere, C., & Anderson, J. R. (1993). A connectionist Implementation of the ACT-R production system. In ''Proceedings of the Fifteenth Annual Conference of the Cognitive Science Society'' (pp. 635–640). Mahwah, NJ: Lawrence Erlbaum Associates]
All of these versions were fully functional, and models have been written and run with all of them.
Because of these implementational degrees of freedom, the ACT-R community usually refers to the "official",
Lisp
A lisp is a speech impairment in which a person misarticulates sibilants (, , , , , , , ). These misarticulations often result in unclear speech.
Types
* A frontal lisp occurs when the tongue is placed anterior to the target. Interdental lisping ...
-based, version of the theory, when adopted in its original form and left unmodified, as "Vanilla ACT-R".
Applications
Over the years, ACT-R models have been used in more than 700 different scientific publications, and have been cited in many more.
Memory, attention, and executive control
The ACT-R declarative memory system has been used to model human
memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
since its inception. In the course of years, it has been adopted to successfully model a large number of known effects. They include the fan effect of interference for associated information,
primacy
Primacy may refer to:
* an office of the Primate (bishop)
* the supremacy of one bishop or archbishop over others, most notably:
** Primacy of Peter, ecclesiological doctrine on the primacy of Peter the Apostle
** Primacy of the Roman Pontiff, e ...
and
recency
Serial-position effect is the tendency of a person to recall the first and last items in a series best, and the middle items worst. The term was coined by Hermann Ebbinghaus through studies he performed on himself, and refers to the finding that r ...
effects for list memory, and serial recall.
ACT-R has been used to model attentive and control processes in a number of cognitive paradigms. These include the
Stroop task
----
----
Naming the font color of a printed word is an easier and quicker task if word meaning and font color are congruent. If two words are both printed in red, the average time to say "red" in response to the written word "green" is ...
,
task switching, the
psychological refractory period
The term psychological refractory period (PRP) refers to the period of time during which the response to a second stimulus is significantly slowed because a first stimulus is still being processed. This delay in response time when one is required t ...
, and multi-tasking.
Natural language
A number of researchers have been using ACT-R to model several aspects of natural
language
Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...
understanding and production. They include models of syntactic parsing, language understanding, language acquisition and metaphor comprehension.
Complex tasks
ACT-R has been used to capture how humans solve complex problems like the Tower of Hanoi, or how people solve algebraic equations. It has also been used to model human behavior in driving and flying.
With the integration of perceptual-motor capabilities, ACT-R has become increasingly popular as a modeling tool in human factors and human-computer interaction. In this domain, it has been adopted to model driving behavior under different conditions, menu selection and visual search on computer application, and web navigation.
Cognitive neuroscience
More recently, ACT-R has been used to predict patterns of brain activation during imaging experiments. In this field, ACT-R models have been successfully used to predict prefrontal and parietal activity in memory retrieval, anterior cingulate activity for control operations, and practice-related changes in brain activity.
Education
ACT-R has been often adopted as the foundation for
cognitive tutors. These systems use an internal ACT-R model to mimic the behavior of a student and personalize his/her instructions and curriculum, trying to "guess" the difficulties that students may have and provide focused help.
Such "Cognitive Tutors" are being used as a platform for research on learning and cognitive modeling as part of the Pittsburgh Science of Learning Center. Some of the most successful applications, like the Cognitive Tutor for Mathematics, are used in thousands of schools across the United States.
Brief history
Early years: 1973–1990
ACT-R is the ultimate successor of a series of increasingly precise models of human cognition developed by
John R. Anderson.
Its roots can be backtraced to the original HAM (Human Associative Memory) model of memory, described by John R. Anderson and
Gordon Bower
Gordon Howard Bower (December 30, 1932 – June 17, 2020) was a cognitive psychologist studying human memory, language comprehension, emotion, and behavior modification. He received his Ph.D. in learning theory from Yale University in 1959. He ...
in 1973. The HAM model was later expanded into the first version of the ACT theory. This was the first time the procedural memory was added to the original declarative memory system, introducing a computational dichotomy that was later proved to hold in human brain. The theory was then further extended into the ACT* model of human cognition.
Integration with rational analysis: 1990–1998
In the late eighties, Anderson devoted himself to exploring and outlining a mathematical approach to cognition that he named
Rational analysis Rational analysis is a theoretical framework, methodology, and research program in cognitive science that has been developed by John Anderson.Anderson, J. R. (1990). "The adaptive character of thought". Hillsdale, NJ: Lawrence Erlbaum Associates. ...
. The basic assumption of Rational Analysis is that cognition is optimally adaptive, and precise estimates of cognitive functions mirror statistical properties of the environment. Later on, he came back to the development of the ACT theory, using the Rational Analysis as a unifying framework for the underlying calculations. To highlight the importance of the new approach in the shaping of the architecture, its name was modified to ACT-R, with the "R" standing for "Rational"
In 1993,
Anderson
Anderson or Andersson may refer to:
Companies
* Anderson (Carriage), a company that manufactured automobiles from 1907 to 1910
* Anderson Electric, an early 20th-century electric car
* Anderson Greenwood, an industrial manufacturer
* Anderson ...
met with Christian Lebiere, a researcher in
connectionist models mostly famous for developing with
Scott Fahlman
Scott Elliott Fahlman (born March 21, 1948) is a computer scientist and Professor Emeritus at Carnegie Mellon University's Language Technologies Institute and Computer Science Department. He is notable for early work on automated planning and sc ...
the
Cascade Correlation learning algorithm. Their joint work culminated in the release of ACT-R 4.0. Thanks to Mike Byrne (now at
Rice University
William Marsh Rice University (Rice University) is a Private university, private research university in Houston, Houston, Texas. It is on a 300-acre campus near the Houston Museum District and adjacent to the Texas Medical Center. Rice is ranke ...
), version 4.0 also included optional perceptual and motor capabilities, mostly inspired from the EPIC architecture, which greatly expanded the possible applications of the theory.
Brain Imaging and Modular Structure: 1998–2015
After the release of ACT-R 4.0,
John Anderson John Anderson may refer to:
Business
*John Anderson (Scottish businessman) (1747–1820), Scottish merchant and founder of Fermoy, Ireland
* John Byers Anderson (1817–1897), American educator, military officer and railroad executive, mentor of ...
became more and more interested in the underlying neural plausibility of his life-time theory, and began to use brain imaging techniques pursuing his own goal of understanding the computational underpinnings of human mind.
The necessity of accounting for brain localization pushed for a major revision of the theory. ACT-R 5.0 introduced the concept of modules, specialized sets of procedural and declarative representations that could be mapped to known brain systems. In addition, the interaction between procedural and declarative knowledge was mediated by newly introduced buffers, specialized structures for holding temporarily active information (see the section above). Buffers were thought to reflect cortical activity, and a subsequent series of studies later confirmed that activations in cortical regions could be successfully related to computational operations over buffers.
A new version of the code, completely rewritten, was presented in 2005 as ACT-R 6.0. It also included significant improvements in the ACT-R coding language. This included a new mechanism in ACT-R production specification called dynamic pattern matching. Unlike previous versions which required the pattern matched by a production to include specific slots for the information in the buffers, dynamic pattern matching allows the slots to be matched to also be specified by the buffer contents. A description and motivation for the ACT-R 6.0 is given in Anderson (2007).
ACT-R 7.0: 2015-Present
At the 2015 workshop, it was argued that software changes required an increment in the model numbering to ACT-R 7.0. A major software change was removal of the requirement that chunks must be specified based on predefined chunk-types. The chunk-type mechanism was not removed, but changed from being a required construct of the architecture to being an optional syntactic mechanism in the software. This allowed for more flexibility in knowledge representation for modeling tasks that require learning novel information and extended the functionality provided through dynamic pattern matching now allowing models to create new "types" of chunks. This also lead to a simplification of the syntax required for specifying the actions in a production because all the actions now have the same syntactic form. The ACT-R software has also been subsequently updated to include a remote interface based on JSON RPC 1.0. That interface was added to make it easier to build tasks for models and work with ACT-R from languages other than Lisp, and the tutorial included with the software has been updated to provide Python implementations for all of the example tasks performed by the tutorial models.
Workshop and summer school
In 1995,
Carnegie Mellon University
Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania. One of its predecessors was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools; it became the Carnegie Institute of Technology ...
began hosting their Annual ACT-R Workshop and Summer School. Their ACT-R Workshop is currently hosted at the annual MathPsych/ICCM Conference, and their Summer School is hosted on-campus with a virtual attendance option at
Carnegie Mellon University
Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania. One of its predecessors was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools; it became the Carnegie Institute of Technology ...
.
Spin-offs
The long development of the ACT-R theory gave birth to a certain number of parallel and related projects.
The most important ones are the PUPS production system, an initial implementation of Anderson's theory, later abandoned; and ACT-RN,
a neural network implementation of the theory developed by Christian Lebiere.
Lynne M. Reder, also at
Carnegie Mellon University
Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania. One of its predecessors was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools; it became the Carnegie Institute of Technology ...
, developed
SAC in the early 1990s, a model of conceptual and perceptual aspects of memory that shares many features with the ACT-R core declarative system, although differing in some assumptions.
For his dissertation at
Carnegie Mellon University
Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania. One of its predecessors was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools; it became the Carnegie Institute of Technology ...
,
Christopher L. Dancy developed, and successfully defended in 2014, ACT-R/Phi,
[Dancy, C. L., Ritter, F. E., & Berry, K. (2012). Towards adding a physiological substrate to ACT-R. In ''21st Annual Conference on Behavior Representation in Modeling and Simulation 2012, BRiMS 2012'' (pp. 75-82). (21st Annual Conference on Behavior Representation in Modeling and Simulation 2012, BRiMS 2012).] an implementation of ACT-R with added physiological modules which enable ACT-R to interface with human physiological processes.
Notes
References
* Anderson, J. R. (2007). ''How can the human mind occur in the physical universe?'' New York, NY: Oxford University Press. .
* Anderson, J. R., Bothell, D., Byrne, M. D., Douglass, S., Lebiere, C., & Qin, Y . (2004). An integrated theory of the mind. ''Psychological Review'', 1036–1060.
External links
Official ACT-R websitewith a lot of online material, including the source code, list of publications, and tutorials
jACT-Ra Java re-writing of ACT-R
ACT-R: The Java Simulation & Development Environmentanother open-source Java re-implementation of ACT-R
PythonACT-Ra Python implementation of ACT-R
pyactranother Python implementation of ACT-R
{{DEFAULTSORT:Act-R
Cognitive architecture
Common Lisp (programming language) software