The fact that the modern world depends on telecom- munication systems that are fundamentally based on the properties and principles identified by Shannon and Weaver (1949) is a clear testament to the useful- ness of information theory. Indeed these early ideas about communication systems and information trans- mission greatly influenced cognitive psychologists. For instance, such ideas provided them with a functional framework for thinking about how the human mind might operate in the abstract. It provided the founda- tions for the assumption that the mind may be char- acterised as an information processing system whereby
had a little lamb, its fleece was white as snow . . .’ (the written sentence is the input) and go on to read it aloud (the spoken sentence is the output). The informa- tion contained in the written form of the sentence is encoded, transmitted and eventually transformed into a spoken output. The underlying operations of encod- ing and transforming the information in the input to produce the output are to be explained in terms of the operations of an information processing system.
The now classical information processing view is that the human organism consists of certain sensory systems (eyes, ears, etc.) which operate as receivers of external inputs; these receivers operate to encode these inputs via sensory encoding or sensory trans- duction. This encoded information is then passed on, via abstract information processing channels, to more central systems. The central systems operate on the information in such a way that an appropriate response can be made. At a distance, this description is very much like a behaviourist S–R theory: an external stim- ulus elicits a response from an organism. However, in attempting to develop functional accounts of beha- viour, cognitive psychologists are mainly concerned with the putative internal (abstract) events that inter- vene between the stimuli and responses. They treat these as being of more importance than the correlative nature of the stimuli and contingent responses. ‘See ‘What have we learnt?’, below.
stimulation at the senses enters into a complex communication system. Indeed the theoretical frame- work dovetailed nicely with other sentiments in the literature about analogies between the operation of the human central nervous system and a ‘complicated telephone switchboard’ (Tolman, 1948, p. 190).
Models of cognitive processing soon began to appear that were based on the central tenets of the so-called
information processing framework. Nonetheless, psy-
chologists were quick to realise that for humans, at least, the notion of the amount of information was more difficult to define than by the simple sorts of statistical measures used in information theory. It is not so much which words are spoken but what mean- ings are trying to be conveyed (MacKay, 1961): ‘dog bites man’ is much less informative than ‘man bites dog’! However, information theory forced psychologists to consider a whole new approach to thinking about human cognition. Now the view was that the human mind could be treated as being an information pro- cessing system: there is some input to an internal com- munication system that is transformed or encoded in particular ways. This encoded information is then transmitted through the system. Eventually, further operations may lead to an output from the system in the form of some sort of observable behaviour.
By way of example, such a system may be posited to explain how it is that you can see the sentence ‘Mary
‘What have we learnt?
Following on from the birth of information theory, psychologists were quick to realise that in trying to explain human nature, something other than stimuli and responses could be quantified and measured. The concept of information came to the fore, and, in turn, information processing accounts of human cognition soon began to emerge. Such accounts hold that a sensory input gives rise to an internal signal that represents the stimulus. That is, the internal signal stands for or designates the stimulus. Hence a phrase that we will repeatedly come across is
stimulus representation. This stimulus representa-
tion is then operated upon in such a way that it can be converted into a behavioural response. The important distinction here is between mental representations and mental processes. The stimulus representation is an internal, mental representation and there are internal processes that operate on such a representation. Mental processes are internal
operations that are invoked once the senses receive stimulation. As we go on to discuss, sensory stimu- lation invokes processes whereby the signal is encoded and transmitted through the human infor- mation processing system.
As cognitive psychologists recognised that the goal was to generate functional information pro- cessing accounts of cognition, it was accepted that such internal representations and processes can be discussed without reference to neurophysiology. Indeed, in laying the foundations for the AI approach to cognitive psychology, Newell, Shaw and Simon (1958) were convinced that the most appropriate way to proceed was to generate working computer programs that mimicked or simulated the particular cognitive ability under consideration. Such ideas as these will be discussed in more detail shortly, but they are very closely linked with something that is known as the computational metaphor of mind.
only get depressed in works of fiction, we have no qualms in stripping our computer bare on the assump- tion that embarrassment is also out of the question (see Figure 2.3). In very simple terms, there is a central processing unit (the CPU that contains an arithmetical unit and a control unit), a program memory, a data memory and a data bus. Operations that are carried out within this system are defined in terms of the sorts of binary coding we have already discussed (see Chapter 1). The computer operates according to the ON/OFF states of its transistors and this is captured by a coding scheme in which a 0 signifies OFF and a 1 signifies ON. This binary code is fundamental and the power and usefulness of the computer rests upon the fact that, to a very large extent, any form of stimulus information can be captured by a signal composed of 0s and 1s. If you remain unconvinced by the awesome power of these two numbers, then it is worth remembering that all your prized DVD of
The Matrix contains is a very well-organised set of
0s and 1s (see Figure 2.4).
The computer shown in Figure 2.3 operates by (i) dividing up these binary signals into workable chunks of, say, 8 characters (or bits) in length such as 00100110, where each 1 and 0 represents a bit in the code; and (ii) shifting these chunks about via the data bus (the main communication channel between the compon- ents). Even the computer program itself is rendered into constituent binary chunks, and these, like the other forms of data, are stored in a particular place in memory (i.e., in the program memory in Figure 2.3). In running the program, the first chunk of the pro- gram code is taken from the program memory and moved via the data bus into the CPU. This CPU is the heart of the computer and is composed of a variety of dedicated temporary stores (or registers) and other components that interpret the current states of the registers. One such register will contain the chunk of program just read from the memory. Let us assume
stimulus representation The phrase used to refer to how a stimulus is encoded following the operation of the perceptual mechanisms.