It is generally agreed that there are three types of memory or memory function: sensory buffers, short-term memory or working memory, and long-term. Sensory memories Attention Short-term memory or working memory Rehearsal Long-term memory Selection of stimuli governed by level of arousal.

sensory memory

• The sensory memories act as buffers for stimuli received through the senses and exists for each sensory channel: -visual stimuli -echoic memory: aural stimuli -haptic memory: tactile stimuli

• Continuously overwritten

Example We can demonstrate the existence of iconic memory by moving a finger in front of the eye. Can you see it in more than one place at once? This indicates a persistence of the image after the stimulus has been removed. -Information is passed from sensory memory into short-term memory by attention -Attention is the concentration of the mind on one out of a number of competing stimuli or thoughts. - Information received by sensory memories is quickly passed into a more permanent memory store, or overwritten and lost.

Short-term memory (STM) • acts as a ‘scratch-pad’ for temporary recall of information. – rapid access ~ 70ms – rapid decay ~ 200ms upto few seconds

Example calculate the multiplication 35 × 6 in your head. The chances are that you will have done this calculation in stages, perhaps 5 × 6 and then 30 × 6 and added the results; or you may have used the fact that 6=2×3 and calculated 2×35=70 followed by 3 × 70. To perform calculations such as this we need to store the inter- mediate stages for use later which uses STM.

Capacity? • STM has a limited capacity. There are two basic methods for measuring memory capacity. The first involves determining the length of a sequence which can be remembered in order. Using the first measure, the average person can remember 7 ± 2 digits. • Look at the following number sequence: 265397620853 Now write down as much of the sequence as you can remember.If you remembered between five and nine digits your digit span is average.

• Now try the following sequence: 92 333 425 8920 • A generalization of the 7 ± 2 rule is that we can remember 7 ± 2 chunks of information. Therefore chunking information can increase the short-term memory capacity.


Recency effect? • Evidence shows that recall of the last words presented is better than recall of those in the middle. This is known as the recency effect.

Long-term memory (LTM) • Here we store factual information, experiential knowledge, procedural rules of behavior – in fact, everything that we ‘know’. - slow access ~ 1/10 second – slow decay, if any – huge or unlimited capacity

• Two types – episodic – serial memory of events – semantic – memory of facts,concepts, skills semantic LTM derived from episodic LTM such that we can learn new facts or concepts from our experiences.

Long-term memory (cont.) • Semantic memory is structured in some way to – provides access to information – represents relationships between bits of information – supports inference(deriving logical conclusions from premises known)

• Model: semantic network:One model for the way in

which semantic memory is structured is as a network. – inheritance – child nodes inherit properties of parent nodes – relationships between bits of information explicit – supports inference through inheritance

LTM - semantic network

Subjects were asked questions about different properties of related objects and their reaction times were measured. The types of question asked were ‘Can a collie breathe?’ ‘Is a beagle a hound?’ ‘Does a hound track?’ -The answers to such questions may seem obvious, subjects took longer to answer questions such as ‘Can a collie breathe?’ than ones such as ‘Does a hound track?’ -Suggested reason is that in the former case subjects had to search further through the memory hierarchy to find the answer, since information is stored at its most abstract level.

Models of LTM - Frames • •

Information organized in data structures Slots in structure instantiated with values for instance of data. Frame slots may contain default, fixed or variable information. • Type–subtype relationships DOG Fixed legs: 4 Default diet: carniverous sound: bark Variable size: colour

COLLIE Fixed breed of: DOG type: sheepdog Default size: 65 cm Variable colour

Models of LTM - Scripts

-Scripts attempt to model the representation of stereotypical(A

stereotype is a belief that may be adopted about specific types of individuals or certain ways of doing things, but that belief may or may not accurately reflect reality.)

knowledge about

situations. -Script has elements that can be instantiated with values for context

Script for a visit to the vet Entry conditions: dog ill vet open owner has money Result: dog better owner poorer vet richer Props: examination table medicine instruments


vet examines diagnoses treats owner brings dog in pays takes dog out

Scenes: arriving at reception waiting in room examination paying Tracks: dog needs medicine dog needs operation

• A script comprises a number of elements, which, like slots, can be filled with appropriate information: -Entry conditions: Conditions that must be satisfied for the script to be activated. -Result: Conditions that will be true after the script is terminated -Props: Objects involved in the events described in the script. -Roles: Actions performed by particular participants. -Scenes: The sequences of events that occur. -Tracks: A variation on the general pattern representing an alternative scenario.

Models of LTM - Production rules -Representation of procedural knowledge, our

knowledge of how to do something. -Information coming into short-term memory can match a condition in one of these rules and result in the action being executed Condition/action rules if condition is matched then use rule to determine action.

IF dog is wagging tail THEN pat dog IF dog is growling THEN run away

Long-term memory processes • There are three main activities related to longterm memory: - storage or remembering of information - Forgetting - information retrieval.

LTM - Storage of information • rehearsal – The repeated exposure to a stimulus or the rehearsal of a piece of information transfers it into long-term memory.

• total time hypothesis – the amount learned is directly proportional to the amount of time spent learning.

• structure, meaning and familiarity – If information is not meaningful it is more difficult to remember

Distribution of practice effect • Learning time is most effective if it is distributed over time. -For example, in an experiment in which Post Office workers were taught to type, those whose training period was divided into weekly sessions of one hour performed better than those who spent two or four hours a week learning (although the former obviously took more weeks to complete their training)

LTM - Forgetting

There are two main theories of forgetting: decay and interference. -decay – information is lost gradually but very slowly

-interference – Retroactive interference:New information causes the loss of old information. A common example of this is the fact that if you change telephone numbers, learning your new number makes it more difficult to remember your old number. This is because the new association masks the old – Proactive inhibition:Old memory trace breaks through and interferes with new information. An example of this is when you find yourself driving to your old house rather than your new one.

LTM - retrieval Two types of information retrieval -Recall – information reproduced from memory can be assisted by cues, e.g. categories, imagery

-Recognition – information gives knowledge that it has been seen before – less complex than recall - information is cue

• Multiple-choice tests are generally easier than fill-in-the-blanks tests or essays because it is easier to recognize the correct answer out of a group of possibilities than it is to have to dredge up the answer out of one’s own head.

Thinking Thinking can require different amounts of knowledge. Some thinking activities are very directed and the knowledge required is constrained. Others require vast amounts of knowledge from different domains. -For example, performing a subtraction calculation requires a relatively small amount of knowledge, from a constrained domain, whereas understanding newspaper headlines demands knowledge of politics, social structures, public figures and world events. -Two categories of thinking:

Reasoning Problem solving

Reasoning • Reasoning is the process by which we use the knowledge we have to draw conclusions or infer something new about the domain of interest.

Deductive Reasoning Deductive reasoning derives the logically necessary conclusion from the given premises. e.g.

If it is Friday then she will go to work It is Friday Therefore she will go to work.

• Logical conclusion not necessarily true: e.g. If it is raining then the ground is dry It is raining Therefore the ground is dry

is a perfectly valid deduction, even though it conflicts with our knowledge of what is true in the world.

Inductive Reasoning • Induction: – Induction is generalizing from cases we have seen to infer information about cases we have not seen.e.g. – all elephants we have seen have trunks therefore all elephants have trunks.

• Unreliable: – However, we can never prove it true because, no matter how many elephants with trunks we have seen or are known to exist, the next one we see may be trunkless.

• Humans not good at using negative evidence • Even if we saw an elephant without a trunk, we would be unlikely to move from our position that ‘All elephants have trunks’, since we are better at using positive than negative evidence. • E.g Wason’s Cards You are presented with four cards. Each card has a number on one side and a letter on the other. Which cards would you need to pick up to test the truth of the statement ‘If a card has a vowel on one side it has an even number on the other’?

Wason's cards

7 E 4 K If a card has a vowel on one side it has an even number on the other Is this true? How many cards do you need to turn over to find out? …. and which cards?

• A common response to this is to check the E and the 4. However, this uses only positive evidence. • To test the truth of the statement we need to check negative evidence: if we can find a card which has an odd number on one side and a vowel on the other we have disproved the statement. We must therefore check E and 7.

Abductive reasoning Abduction reasons from a fact to the action or state that caused it. This is the method we use to derive explanations for the events we observe.

• reasoning from event to cause e.g. Sam drives fast when drunk. If I see Sam driving fast, assume drunk.

• Unreliable: – since there may be another reason why she is driving fast: she may have been called to an emergency, for example.

Problem solving • 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 and earliest dates back to the first half of the twentieth century, is the Gestalt view that problem solving involves both reuse of knowledge and insight.

Gestalt – It was believed that problem solving is only reproductive(that problem solving is a matter of reproducing known responses or trial and error) – Gestalt said that problem solving is both productive and reproductive – reproductive problem solving draws on previous experience as it was claimed, but productive problem solving involves insight and restructuring of the problem.

Errors and mental models Types of error • slips – – –

right intention, but failed to do it right causes: poor physical skill,inattention etc. change to aspect of skilled behaviour can cause slip

• mistakes – –

wrong intention cause: incorrect understanding humans create mental models to explain behaviour. if wrong (different from actual system) errors can occur

Emotion Our emotional response to situations affects how we perform. Positive emotions enable us to think more creatively, to solve complex problems, whereas negative emotion pushes us into narrow, focussed thinking. A problem that may be easy to solve when we are relaxed, will become difficult if we are frustrated or afraid.

Emotion (cont.) • Implications for interface design – stress will increase the difficulty of problem solving – relaxed users will be more forgiving of shortcomings in design – aesthetically pleasing and rewarding interfaces will increase positive affect

Individual differences

although we share processes in common, humans, and therefore users, are not all the same. We should be aware of individual differences so that we can account for them as far as possible within our designs


• long term – gender, physical and intellectual abilities • short term – effect of stress or fatigue • changing – age

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