Human Computer Interaction Lecture 2 The Human

The Human Think of human as an information processing system, which contains input/output, stores information and processes information We will therefore consider three components of this system: input-output, memory and processing

The Human Information i/o … Information stored in memory visual, auditory, haptic, movement Information stored in memory sensory, short-term, long-term Information processed and applied reasoning, problem solving, skill Emotion influences human capabilities Each person is different

Vision Two stages in vision • physical reception of object • processing and interpretation of object

The Eye - physical reception mechanism for receiving light and transforming it into electrical energy light is reflected from objects images are focused upside-down on retina retina contains rods for low light vision. Rods are responsible for vision in darkness. Approximately 120 million rods.

The Eye - physical reception Retina also contains cones for colour vision. They are responsible for vision in light. Cones are concentrated on fovea and rods are concentrated on retina Blind spot contains neither rods nor cones. Ganglion cells (brain!) detect pattern and movement

Design Focus A user concentrating on the middle of the screen cannot be expected to read help text on the bottom line. So if an error message is to be shown to user, what to do??? Better use flashing error message

Interpreting the signal Brightness subjective reaction to levels of light affected by luminance of object, which is the amount of light emitted by an object Contrast is luminance of object and luminance of its background High display luminance systems are seen to flicker even above 50 Hz.

Interpreting the signal (cont) Colour made up of hue, intensity, saturation Hue is determined by the spectral wavelength of the light Approximately 150 different hues can be discriminated by the average person Intensity is the brightness of color Saturation is the amount of whiteness in color Cones are sensitive to colour wavelengths. Three types of cones (red, green and blue) blue acuity is lowest, because only 3-4% of the fovea is occupied by cones which are sensitive to blue light 8% males and 1% females colour blind

Optical Illusions the Muller Lyer illusion the Ponzo illusion

Reading Several stages: visual pattern perceived decoded using internal representation of language interpreted using knowledge of syntax and semantics Reading involves saccades(jerky movements) and fixations Perception occurs during fixations Word shape is important to recognition Negative contrast (dark character on a light screen) improves reading from computer screen

Design Focus Standard font sizes of 9 to 12 are equally readable, given proportional spacing between lines. Similarly line lengths of between 2.3 and 5.2 inches (58 and 132 mm) are equally legible. Nevertheless, reading from a computer screen is slower than from a book. However, this fact can be controlled by careful design of textual interfaces.

Hearing Sound can convey a remarkable amount of information Provides information about environment: distances, directions, objects etc. Physical equipment: outer ear – protects inner and amplifies sound middle ear – transmits sound waves as vibrations to inner ear inner ear – chemical transmitters are released and cause impulses in auditory nerve Sound pitch – sound frequency loudness – amplitude timbre – type or quality

Hearing (cont) Humans can hear frequencies from 20Hz to 15kHz less accurate distinguishing high frequencies than low. Auditory system filters sounds can attend to sounds over background noise. for example, the cocktail party phenomenon. Sound could be used extensively in interface design to convey information about the system state.

Touch Provides important feedback about environment. May be key sense for someone who is visually impaired. Stimulus received via receptors in the skin: thermoreceptors – heat and cold nociceptors – pain mechanoreceptors – pressure Some areas more sensitive than others e.g. Fingers and hair

Memory There are three types of memory function: Sensory memories Short-term memory or working memory Long-term memory Attention Rehearsal

Sensory Memory Buffers for stimuli received through senses iconic memory: visual stimuli echoic memory: aural stimuli haptic memory: touch stimuli Examples: touch a cup of tea Information is passed to STM by attention

Short-term memory (STM) What is the result of 35 * 6??? Scratch-pad for temporary recall rapid access rapid decay

Examples 21234827849320245456 21234 482784 932024 5456 03323583302 0332-35-83-302 ATM Card example