1) Introduction - [Background and History]
Early computers were usually batch programmed:
Ø Tasks (programmed and data) prepared off-line.
Ø Batch of tasks loaded and run in sequence.
Ø Operator intervention limited to loading batches.
Ø No intervention whilst batch is running.
In recent years, new challenges and possibilities have emerged:
Ø Computers have become smaller and cheaper
Ø New interaction technologies have been developed.
Ø Legislation has raised standards, particularly with regards to accessibility.
Accessibility means giving users with special needs the same level of access as other users.
For example, people who are blind/visually impaired can operate GUIs with the aid of a screen-reader.
However, compared to other users, screen-reader usually tends to:
Ø work more slowly
Ø make more errors
Ø report higher level of fatigue
Thus, while visually impaired people can user GUIs, it cannot be said that they have the same level of access as other users.
As computers become cheaper and more powerful, we are seeing a move from reactive systems to adaptive/proactive systems:
Ø Reactive Systems
Ø User always initiates actions
Ø Large screens, focus on user attention
Ø Little need for adaptivity
Ø Proactive Systems
Ø System or user can initiate actions
Ø No-screen/hands free, user attention elsewhere
Ø Adaptivity essential for effective operation
2) Introduction - [Issues and Topics]
"A user interface should be so simple that a beginner in an emergency can understand it within ten seconds"
"..Any application designed for people should be:
Ø Easy to learn( and remember )
Ø Useful, that is, contain functions that people really need in their work, and
Ø Be easy and pleasant to use."
Four Key Concepts
Ø Learnability - the time and effort required to reach a specified level of user performance.
Ø Throughput - tasks accomplished, speed of execution, errors made, etc.
Ø Flexibility - the extent to which the systems can accommodate changes to the tasks and environments beyond those first specified.
Ø Attitude - the attitude engendered in users by the application.
For example:
Ø A travel agent (primary user) may use a system to search for hotels, flights, trains, etc., on behalf of...
Ø A customer( secondary user )
3) Human Memory & Perception - [Memory]
Human memory as three distinct stages. Information is:
1. Received through one or more of the sensory memories e.g.
Ø Iconic( visual ) memory
Ø Ethoic( auditory ) memory
Ø Haptic memory
2. Selectively held in short term memory while it is analyzed, after which is may be either discarded or...
3. Stored permanently in long term memory
The short term memory can hold around seven items of information
However, it is not easy to define an "item of information". An item might be:
Ø A single digit or character or word, or...
Ø A long number or entire phrase, if that number or phrase is already known by the person
There are two types of long term memory:
Ø Episodic Memory represents our memory of events and experiences - It stores items in serial form, allowing us to reconstruct sequences of events and experiences from earlier points in our lives.
Ø Semantic Memory is structured so that is represents relationships between information - it stores information without regard to the order in which it was acquired or the sense through which it was acquired.
There are three main processes associated with long term memory (LTM):
Ø Storage/remembering
Ø Forgetting
Ø Information Retrieval
Information passes into long term memory via the short term memory.
However, not everything that is held in short term memory is eventually stored in long term memory.
The main factors that determine what is stored are:
Ø Rehersal
Ø Meaning
Rehersal, i.e. repeated exposure to data, or consideration of it, increases the likelihood that it will be stored in LTM.
Meaningful information is more likely to be stored in LTM than meaningless data.
There are two main theories to explain the loss of information from long term memory: decay or interference.
Ø Decay: Ebbinghaus concluded that information is lost through natural decay.
Ø Interference: new information may replace or corrupts older information.
Ø For example, changing your telephone number may cause you to forget your old number. This is known as retroactive interference.
Ø However, there may also be times when older information 'resurfaces' and becomes confused with newer information. For example, you may suddenly recall an old telephone number and confuse it with your new one. This is known as proactive inhibition.
There are two types of information retrieval from LTM:
Ø Recall: the recovery of information as a result of a conscious search.
Ø Recognition: the automatic recovery of information as a result of an external stimulus.
Recognition is around twice as fast and three times as accurate as recall.
4) Human Memory & Perception - [Visual Perception]
The human visual system can be divided into two stages:
Ø Physical reception of light
Ø Processing and interpretation
The human visual system has both strengths and weaknesses:
Ø Certain things cannot be seen when present
Ø Processing allows images to be constructed from incomplete information
Light passes through the cornea and is focused by the lens producing and inverted image on the retina.
The iris regulates the amount of light entering the eye.
The retina is covered with photoreceptors. These are of two types:
Ø Rods; high sensitivity to light, see's black and white colors, low resolution
Ø Cones; low sensitivity to light, see's color( red, green, black ), high resolution
The eye contains:
Ø around 120 million rods, most of which are located around the periphery of the retina
Ø around 6 million cones, most of which are located in the fovea
The lens is flexible and can focus the image on different parts of the retina.
This makes it possible to adapt between light and dark conditions:
Ø In bright conditions, light is focused on the fovea, giving high resolution and color vision
Ø In dark conditions, focus is shifted onto the periphery, giving greater sensitivity but reducing resolution and color perception.
The retina contains ganglion cells which perform some local processing of images.
There are two types of ganglion cells:
Ø X-Cells
Ø perform basic pattern recognition
Ø mainly concentrated in the fovea
Ø Y-Cells
Ø perform movement detection
Ø more widely distributed than X-Cells, and predominate the periphery
The photo-receptors and ganglion cells are all connected to the optic nerve, which carries visual information to the brain.
There are no photo-receptors in the area of the retina around the optic nerve.
Thus there is a blind spot at this point.
We are not usually aware of the blind spot because our brains ‘fill in' the missing part of the image.
The luminance of an object depends on:
Ø the amount of light falling on its surface
Ø the reflective properties of the surface(s)
Contrast is related to luminance. It is the difference in luminance between the brightest and darkest areas of an image.
The human visual system compensates for bright or dark conditions by varying the relative percentage of rods and cones it uses.
The human eye can distinguish about 150 hues within the visible light spectrum.
However, the total number of colors we can distinguish is much higher.
This is because:
Ø Each of the pure hues can be mixed with white in various quantities to produce other colors.
Ø We refer to the spectrum of hues as fully-saturated colors.
Ø When mixed with white, we refer to them as partially-saturated or de-saturated colors.
Ø The brightness of each color can be varied:
In practice, we use a limited number of primary colors, e.g.:
Ø Red, Green and Blue( RGB ) when mixing light
Ø This is known as additive mixing.
Ø Cyan, Magenta, Yellow and Black( CMYK ) when mixing pigments
Ø This is known as subtractive mixing.
Factors affecting our judgement of size include:
Ø Stereo vision - the difference in the image seen by each eye can be analysed to gauge distances
Ø Head Movement - small changes in viewing position produce changes in view that allow distance to be gauged
Ø Monocular Cues:
Ø Relative size
Ø Relative height
Ø Relative motion
When children learn to read, they initially read linearly, i.e.
Ø start at the beginning of the sentence
Ø read each word in turn
Ø identify the meaning of each word
Ø identify the meaning of the sentence
This is a very slow and inefficient method of reading.
As they become more proficient at reading they learn to scan text by spotting key-words.
This process involves the following stages:
Ø Identify a word or character
Ø Guess the meaning of the phrase of sentence
Ø Confirm/disaprove the guess
Ø Revise the guess if necessary
A number of methods are used to measure the readibility of text:
Ø Average reading time
Ø A group of people are asked to read the text, and the average time taken is noted.
Ø Fog Index
Ø Takes into account word-length, sentence-complexity, etc.
Ø Cloze Technique
Ø Subjects are asked to read a piece of text in which every fifth word is blanked out.
Ø The index is based on the percentage of blanked words that are guessed correctly.
Factors that affect the readability of text include:
Ø Font-style and capitalization
Ø Font size
Ø Character spacing
Ø Line Lengths
5) Human Memory & Perception - [Auditory Perception]
Like the visual system, the human auditory system can be divided into two stages:
Ø Physical reception of sounds
Ø Processing and interpretation
Like the visual system, the human auditory system has both strengths and weaknesses:
Ø Certain things cannot be heard even when present
Ø Processing allows sounds to be constructed from incomplete information
The principal characteristics of sound - as perceived by the listener - are:
Ø Pitch
Ø Loudness
Ø Timbre
The perceived intensity of a sound depends upon:
Ø The sound pressure.
Ø The distance between the source and the listener.
Ø The duration of the sound.
Ø The frequency of the sound.
Our hearing system allows us to determine the location of sound sources with reasonable accuracy, subject to certain limitations.
Ø Stereo hearing allows us to locate the source of a sound by comparing the sound arriving at each ear and noting differences in:
Ø Amplitude
Ø Time of arrival
Ø Head movement allows us to improve the localization accuracy of stereo hearing
Ø Analysis of reflected vs direct sound allows us to localize both the horizontal and vertical planes - to a limited extent
Ø Familiarity affects localization accuracy
Judgment of distance is based partly on intensity - the quicker the sound, the farther away the source.
Sound localization (in both horizontal and vertical planes) can be improved by tailoring the sound distribution.
This is done using Head-Related Transfer-Functions (HRTFs).
Ideally, HRTFs should be tailored to suit the individual. However, this is complex and costly.
Researchers are currently trying to develop non-individualized HRTFs which will give a useful improvement in localization accuracy for a substantial percentage of the population.
Research suggests that the human auditory system includes a short-term store - a kind of mental 'tape loop' that always stores the last few seconds of sound.
This is known as the Pre-categorical Acoustic Store or PAS.
Researchers disagree as the length of the store. Estimates range from as little as 10 seconds to as much as 60 seconds.
However, there is significant evidence for the existence of such a store.
The existence of this auditory store explains some of the following effects.
Ø Recall of Un-attended Material
Ø The Recency Effect
Ø If someone listens to a voice reciting a list of digits (or characters etc.) and is then asked to repeat the digits, he or she will recall the last few digits more reliably than the earlier ones.
Ø Typically the last 3 - 5 digits are recalled.
Ø The Auditory Suffix Effect
Ø The recency effect (see above) is most noticeable when the speech or sound is followed by a period of silence.
Ø If a further sound occurs after (e.g.) a list has been spoken recall is impaired.
Ø Conversely, if speech or sound is followed by complete silence, the period for which the last few seconds of it can be recalled extends significantly.
6) Human Memory & Perception - [Haptic Perception]
Haptic Perception is the general term covering the various forms of perception based on touch.
There are three types of sensory receptor in the skin:
Ø thermoreceptors respond to heat and cold
Ø mechanoreceptors respond to pressure
Ø nociceptors respond to intense heat, pressure or pain
In computing applications, we are mostly concerned with mechanoreceptors.
Mechanoreceptors are of two types:
Ø rapidly-adapting mechanoreceptors react to rapid changes in pressure, but do not respond to continuous pressure
Ø slowly-adapting mechanoreceptors respond to continuous pressure
Sensory acuity is often measured using the two-point test.
This simply involves pressing two small points (ed. sharpened pencil tips) against the body.
The two points are initially placed very close together, and then moved further apart until it becomes possible to feel two distinct pressure points rather than one.
The smaller the distance at which both points can be detected, the greater the sensory acuity.
The fingers and thumbs have the greatest acuity.
Sensory acuity varies considerably among individuals.
It can be improved with training, within certain limits.
For example, blind people who read Braille generally have better sensory acuity than non-Braille readers.
However, certain medical conditions can lead to reduced sensory acuity.
Kinaesthetic Feedback
Another aspect of haptic perception is known as kinaesthetic feedback.
Kinaesthetic receptors in our joints and muscles tell us where our limbs, fingers, etc., are relative to the rest of our body.
Kinaesthetic receptors are of three types: