Read the text and describe human memory using the diagram below.

Human Memory. There are generally three types of memory: sensory memory, short-term memory and long-term memory.

Sensory memory. The sensory memories act as buffers for stimuli received through the senses. A sensory memory exists for each sensory channel: iconic memory for visual stimuli, echoic memory for aural stimuli and haptic memory for touch. Information is passed from sensory memory into short-term memory by attention, thereby filtering the stimuli to only those which are of interest at a given time.

Short-term memory. Short-term memory acts as a scratch-pad for temporary recall of the information under process. For instance, in order to understand this sentence you need to hold in your mind the beginning of the sentence you read the rest.

Short term memory decays rapidly (200 ms.) and also has a limited capacity. Chunking of information can lead to an increase in the short term memory capacity. Thst is the reason why a hyphenated phone number is easier to rememeber than a single long number. The successful formation of a chunk is known as closure. Interference often causes disturbance in short-term memory retention. This accounts for the desire to complete the tasks held in short term memory as soon as possible.

Long-term memory. Long-term memory is intended for storage of information over a long time. Information from the working memory is transferred to it after a few seconds. Unlike in working memory, there is little decay.

There are two types of long-term memory: episodic memory and semantic memory. Episodic memory represents our memory of events and experiences in a serial form. It is from this memory that we can reconstruct the actual events that took place at a given point in our lives. Semantic memory, on the other end, is a structured record of facts, concepts and skills that we have acquired. The information in semantic memory is derived from that in our own episodic memory, such that we can learn new facts or concepts from our experiences.

Long-term memory processes. There are three main activities related to long term memory: storage, deletion and retrieval.

Information from short-term memory is stored in long-term memory by rehearsal. The repeated exposure to a stimulus or the rehearsal of a piece of information transfers it into long-term memory. Experiments also suggest that learning time is most effective if it is distributed over time. Deletion is mainly caused by decay and inerference. Emotional factors also affect long-term memory. However, it is debatable whether we actually ever forget anything or whether it becomes increasingly difficult to access certain items from memory. Having forgotten something may just be caused by not being able to retrieve it! Information may not be recalled sometimes but may be recognized, or may be recalled only with prompting. This leads us to the third process of memory: information retrieval.

There are two types of information retrieval: recall and recognition. In recall, the information is reproduced from memory. In recognition the presentation of the information provides the knowledge that the information has been seen before. Recognition is of lesser complexity, as the information is provided as a cue. However, the recall can be assisted by the provision of retrieval cues which enable the subject to quickly access the information in memory.

Thought processes. Cogito ergo sum (I think therefore I am). These words of Descartes sum up the importance of thought processes in humans and probably the most important reason we differ from animals. Although animals retrieve and store information, there is little evidence to suggest that they can use it in quite the same way as humans. Humans, on the other hand, are able to use information to reason and solve problems, even when the information is partial or unavailable.

Thinking can be categorized into reasoning and problem solving. Although these are not distinct they are helpful in clarifying the processes involved.

Reasoning. Reasoning is the process by which we use the knowledge we have to draw conclusions or infer something we know about the domain of interest. Reasoning is classified as being deductive, inductive or abductive. Deductive reasoning involves deciding what must be true given the rules of logic and some starting set of facts (premises). Inductive reasoning involves deciding what is likely to be true given some starting set of beliefs or observations.

Deductive reasoning. Deductive reasoning derives the logically necessary conclusion from the given premises. It is important to note that it can lead to a logical conclusion which conflicts with our knowledge of the world. For example, if it is raining then the ground is dry. It is raining. Therefore the ground is dry. It is a perfectly valid deduction! Deductive reasoning is therefore often misapplied. Human deduction is at its poorest when truth and validity clash. This is because people bring their knowledge of the real world into the reasoning process as it allows them to take short cuts which make information processing more efficient.

Inductive reasoning. Induction is generalizing from cases we have seen to infer information about cases we haven’t. For instance, if all the dogs that we have seen are white, we may infer that all dogs are white in colour. This is disproved when we see a black dog! In the absence of counter examples, all that we can do is gather evidence to support our inductive inference. In spite of its unreliability, induction is a useful process which we use constantly in learning about our environment.

Abductive reasoning. Abduction reasons from a fact to the action that caused it. This is the method we use to derive explanations for the events we observe. This kind of reasoning, although useful, can lead to unreliability as an action preceding an event can be wrongly attributed as the cause of the event.

Problem solving.Problem solving is the process of finding a solution to an unfamiliar task, using the knowledge we have. There are a number of different views of how people solve problems. We shall consider two of the more recent and influential views: Gestalt theory and the problem space theory.

Gestalt theory. Gestalt theory claims that problem solving is productive and reproductive. Reproductive problem solving draws on previous experiences whereas productive problem solving involves insight and restructuring of the problem. Reproductive problem solving could be a hindrance to finding a solution, since a person may fixate on the known aspects of a problem and so be unable to see novel interpretations that might lead to a solution. A well known example of this is Maier’s `pendulum problem’. The problem was to tie together pieces of string hanging from the ceiling. However, they were far too apart to catch hold of both at once. The room was full of other objects including pliers, poles and extensions. Although various solutions were proposed by participants, few chose to use the weight of the pliers as a pendulum to swing the strings together. However, when the experimenter brushed against the string, setting it in motion, a lot of participants came up with the idea. This can be interpreted as an example of productive restructuring. This experiment also illustrates fixation: participants were unable to see any method beyond the use of a pair of pliers.

Problem space theory. The problem space theory was proposed by Newell and Simon. The theory says that problem solving centers around the problem space. This space comprises of problem states which can be generated using legal transition operators.

For example, imagine you are reorganizing your office and you want to move the desk from one end to another. The two different states are represented by the locations of the desk. A number of operators can be applied to move these things: they can be carried, pushed, dragged etc. In order to ease the transition between the states, you have a new sub-goal: to make the desk light. These may involve operators such as removing drawers and so on.

Within the problem space framework, experience allows us to solve problems more easily since we can structure the problem space appropriately and choose operators efficiently.

Analogy in problem solving. People solve novel problems by mapping knowledge in a similar known domain to it. For instance, to destroy malignant tumour it is essential to fire low intensity rays from all sides, as high intensity rays can damage healthy tissues. An analogous case is that of attacking a fortress. However, people miss analogous information unless it is semantically close to the problem domain.

Skill acquisition. Skills in a given problem area differentiate the novice from the expert. A commonly studied domain is chess playing. It is particularly suitable since it lends itself to representation in terms of problem space theory, in which the initial board configuration and the final position constitute the states while the moves appeared as transition operators. Masters took lesser time than novices to react to a situation and produced better moves. This is largely because chess masters remember board configurations and good moves associated with them. They can chunk the board configuration in order to hold it in short-term memory.

Skilled behavior becomes automatic over a period of time. Experts tend to mentally rehearse their actions in order to identify exactly what they do. Although such skilled behavior is efficient it may cause errors when the context of the activity changes.

Individual differences. The psychological principles and properties that have been discussed apply to the majority of people. However, there are individual differences which affect a small percentage. The differences may be long term such as sex, physical capabilities and individual capabilities. Others are for a shorter duration and may include the effects of stress or failure on the user. Still others may change through time such as age. These differences should be taken into account in interface designs to eure that a grensater population of users is benefited.