CSCD 487/587Human Computer Interface

Winter 2013

Lecture 8Human Movement and Memory

Overview

Few more thoughts on humans and their abilities

How do movements relate to interface design?

How much information can we deal with?

How complex should the information be on a screen?

Look at movements, and memory

Human Memory

Human MemoryBasic Questions How does information get into memory? How is information maintained in memory? How is information pulled back out of memory?

Three processes– Encoding, Storage and Retrieval

Figure 7.2 Three key processes in memory

Memory Encoding

Encoding is crucial first step to creating a new memory

It allows perceived item of interest to be converted into a construct that can be stored within brain,

Recalled later from short-term or long-term memory.

Memory Encoding

Encoding is a biological event beginning with perception through senses

Process of laying down a memory begins with attention

Memorable event causes neurons to fire more frequently, making experience more intense and increasing likelihood that event is encoded as memory

Memory Encoding Perceived sensations are decoded in

various sensory areas of cortex, and then combined in brain’s Hippocampus into one single experience

Hippocampus is then responsible for analyzing these inputs and deciding if they will be committed to long-term memory

It acts as kind of sorting center where new sensations are compared and associated with previously recorded ones

Various threads of information are then stored in various different parts of the brain,

Figure 7.23 The anatomy of memory

Storage: Maintaining Information in Memory Information storage in computers is similar Information storage in human memory

Subdivide memory into 3 different stores• Sensory,

Iconic - visual stimuli

Echoic - aural stimuli

Haptic - touch stimuli• Short-term,• Long-term

Figure 7.7 The Atkinson and Schiffrin model of memory storage

Sensory Memory Shortest term memory

Retain impressions after original stimulii ended

Ultra short memory decays quickly 1/5 to ½ second

Is the first step to storing in short term memory

Information is passed to short term memory via attention

Placing attention on it filters stimuli that is of interest

Short Term Memory Next in line from sensory memory

Scratch pad for temporal recall Brain's post-it notes, holds small amount

of information 7 + or – 2 items Recall for short period of time, 10 – 15

secs Example: To understand an entire

sentence when you read it, hold beginning of sentence in short term memory

Next step towards long-term memory One way to transfer to long-term storage Working memory is short term memory

Short Term Memory

If memory is to be stored in long-term memory some type of transfer takes place in few seconds

Rehearsal – the process of repetitively verbalizing or thinking about the information

This is where chunking takes place to help with memory recall:

Long Term Memory Memories come to Long-term storage

through short term storage Process of consolidation by rehearsal

and meaningful association Encodes information semantically Process involves physiological changes

to brain – neural networks are created With repeated use, efficiency of neural

networks increases Storage occurs throughout brain

Slow access - 1/10 second Slow decay, if any Huge or unlimited capacity

Long-term MemorySemantic memory structure Provides access to information Represents relationships between bits of information Supports inference

Model: Semantic network Inheritance - child nodes inherit properties of parent nodes Relationships between information - explicit Supports inference through inheritance

works sheephas four legs

barks ANIMAL is a SHEEPDOG

breathes is a DOG

moves has tail is a

is a size: medium COLLIE

color: [brown/white, black/white, merle]

HOUND instance instance

tracks is a LASSIE

SHADOW

film character size: small

BEAGLE color: brown/whitebook character color: brown/white

color: [brown, black/white] instance

SNOOPY

cartoon/book character friend of

CHARLIE BROWN

Semantic network model of LTM

Other Models of Long Term MemoryFrames:Information organized in data structureSlots in structure are instantiated with particular values for a given instance of data. DOG

Fixed

legs: 4

Default

diet: carnivorous

sound: bark

Variable

size:

color

COLLIEFixed breed of: DOG type: sheepdogDefault size: 65 cmVariable color

Script for a visit to the vet

Entry conditions: dog ill Roles: vet examines vet open diagnoses owner has money treats owner brings dog in paysResult: dog better takes dog out owner poorer vet richer Scenes: arriving at reception waiting in room examination Props: examination table paying medicine instruments Tracks: dog needs medicine dog needs operation

Other Models of long-term Memory

Scripts:Model of stereotypical information required to interpret situation or language.

Accessing MemoriesRetention – the proportion of material

retained Recall Recall is a way that you obtain

information from your memory without having a cue to prompt the response. You have to essentially draft the information without any assistance.

Recognition Recognition is how you respond to a sensory cue. You look at something and your mind looks to see if what you are seeing in front of you matches anything that has been stored. If you notice a match, you are recognizing the information.

Example: Taking a test, multiple choice is recognition, short answer is recall

Figure 7.16 Ebbinghaus’ forgetting curve for nonsense syllables

Figure 7.17 Recognition versus recall in the measurement of retention

Long Term Memory How do we forget information?

When neural networks become weak from lack of use

When we impose new neural networks on top of old networks causing interference with old network

Memory is selective and affected by emotion - can “choose” to forget

Also varies by sex, physical and intellectual abilities

Changes with age

Figure 7.19 Retroactive and proactive interference

Memory Implications for Design

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Recognition over Recall

As we said ...Recall

Info reproduced from memory, no cuesRecognition

Presentation of info provides knowledge that info has been seen before

Easier because of cues to retrievalWe want to design UI's that rely on recognition!

Short term Memory Limits

Misconception that limited short-term memory should be limited to 7 items!!!

It's fine to have longer menus (if needed)– Users don't have to memorize the full

list of menu items The entire idea of a menu is to rely on

recognition rather than recall But if you make a menu too short, the

choices become overly abstract and obscure.

Specifically for Web Design

Response times must be fast enough that users don't forget what they're in the middle of doing while waiting for the next page to load

Change color of visited links so that users don't have to remember where they've already clicked

Also counts as providing feedback to users

Specifically for Web Design

Offer help and user assistance features in the context where users need them

So they don't have to travel to a separate help section and memorize steps before returning to the problem at hand

This goes for other non-web interfaces too

Individual Differences

Huge individual differences in user performance

Top 25% of users are 2.4 times better than the bottom 25%

Only about 4% of the population has enough brainpower to perform complex cognitive tasks such as making high-level inferences using specialized background knowledge

If you forget these limits, users will find your site very frustrating

Measuring Motor Movement

Movement – Fitt’s Law• Fitts' Law, 1954

–Fundamental law of human sensory-motor system–Practical application in interface design–Describes the time taken to hit a screen target

–Time, Mt, to move hand to a target of size, S, at distance, D, away

Mt = a + b log2(D/S + 1)

where: a and b are empirically determined constantsMt is movement timeD is Distance S is Size of target

– “index of difficulty”: log2(D/S + 1)• Same performance at greater distance with greater size

targets as large as possible, distances as small as possible

Fitt’s Law

Which is the easiest to hit?

HIT MEHIT ME

4 cm 4 cm

1 cm

5 cm

T = 100 log2(4/1 + 0.5) = 9 ms

T = 100 log2(4/5 + 0.5) = 2.6 ms

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Fitts’ Law Example

Which is the easiest to hit?

TodaySundayMondayTuesday

WednesdayThursday

FridaySaturday

Pop-up Linear Menu Pop-up Pie Menu

Fitt’s Law Implications

• Hierarchical menus are hard to hit– Especially when it takes two actions …

Take a Quiz

Try out Fitt's Law Concepts from AskTog

http://www.asktog.com/columns/022DesignedToGiveFitts.html

Summary

Human memory models important – Otherwise, we as designers will

underestimate or overestimate our users

– Users will get frustrated if their mental capacities are not accounted for in products they use !!!

References

Short-Term Memory and Web Usability by J. Nielsen

http://www.nngroup.com/articles/short-term-memory-and-web-usability/

Human Memory

http://www.human-memory.net/brain_parts.html

The End

Reading … on to Chapter 4