The Turing Machine, the Computational Theory of Mind, and the PSSH
- The Turing Machine: Conceived by mathematician Alan Turing, this theoretical machine was designed to solve computable problems, such as the “halting problem”. It operates using an algorithm to read, edit (write or erase), and move along an infinitely long piece of tape containing discrete symbols. In cognitive science, this abstract model serves as a foundational analogy for how the human mind might process information through formal rule-based algorithms.
- The Computational Theory of Mind (CTM): This framework posits that the human mind acts as an information processor analogous to a computer or Turing machine. Within CTM, cognitive processes are understood as the rule-governed manipulation and transformation of internal symbolic representations.
- Physical Symbol System Hypothesis (PSSH): Formulated by Newell and Simon, the PSSH provides a concrete assertion of CTM. It states that any physical computational system that manipulates formal symbols contains the necessary and sufficient means for general intelligent action. Symbols are physical patterns that can combine to form complex structures, and the system uses specific algorithms to generate and transform these symbols.
Representations, and how they work
- Representations are the fundamental formats used to encode the information the mind perceives, stores, and manipulates. They rely on four key aspects: a representation bearer (like a human or computer), content (meaning), grounding (a connection to the external world/referent), and interpretability.
- They are connected to objects in the real world through Intentionality, which is the mind’s directedness toward an external stimulus. Intentionality features isomorphism (a similarity of structure between the representation and the referent) and an appropriate causal relationship between inputs and outputs.
- Formats of Representation:
- Digital (Symbolic): Information is coded in a discrete way with set values, such as written letters or numbers.
- Analog: Information is represented continuously, preserving the physical and spatial/geometric properties of the referent, such as a visual image or an analog clock.
- Propositional: Abstract, sentence-like logical structures (predicate calculus) that specify the deep relationships between concepts independently of their visual or verbal elements.
- The Dual-Coding Hypothesis suggests that humans can represent many concrete concepts using both analog (visual) and digital (verbal) codes simultaneously.
Top-down and Bottom-up Processing and how they work
- Top-down Processing: This cognitive pathway relies heavily on preexisting cognitive schemas and stored knowledge to interpret environmental stimuli and fill in missing information. For example, when reading the words “the cat,” the mind can deduce the meaning even if the middle letters are ambiguous or malformed. Visual illusions, such as the Müller-Lyer illusion (where identical lines appear to be different lengths due to surrounding arrow angles), highlight failures of top-down processing when preexisting structural schemas misinterpret stimuli.
- Bottom-up Processing: This pathway constructs a perception directly from the raw, fine-grained features of a stimulus itself. A key example is the Demon (Pandemonium) Model, where localized “image demons” detect basic sensory features (like brush strokes or lines), synthesizing them upwards through “pattern demons” until a final “decision demon” categorizes the whole object.
- David Navon’s concept of Global Precedence suggests that top-down, global identification typically occurs faster and takes precedence over localized, bottom-up feature detection.
The Working Memory Subsystems
- Working Memory is the cognitive process responsible for the immediate manipulation and temporary storage of information.
- The Central Executive Working Memory Model breaks this into specific subsystems:
- The Central Executive: The central control hub that coordinates the modality-specific subsystems.
- The Phonological Loop: Retains auditory and verbal information primarily through internal repetition. Engaging in repetitive verbal tasks disrupts its capacity, a phenomenon known as articulatory suppression.
- The Visuospatial Sketchpad: A dedicated subsystem for encoding and manipulating geometric space and visual information.
- The Episodic Buffer: A mechanism that integrates multimodal information from different sensory sources (such as combining auditory and visual inputs) and is essential for feature binding.
Chomsky’s Transformational Grammar
- Developed by Noam Chomsky, this linguistic framework illustrates how language functions similarly to an algorithm, allowing a finite set of rules to generate infinite complex meanings.
- Deep Structure: The fundamental linguistic rules and semantic categories that establish the actual underlying meaning behind an arrangement of words.
- Surface Structure: The apparent physical arrangement or order of words, which can be changed without altering the deep structural meaning.