HCI Ch-2-Sadiq.pdf

Human-Computer Interaction Lecture 2 Dr. Eng. Sadiq Ghalib In this lecture The Human ○ Information Processing Model ○ Input/Output channels Human Modeling The Model of Human Processor; Card, Moran and Newell, 1983 The model comprises three subsystems: t...

Human-Computer Interaction Lecture 2 Dr. Eng. Sadiq Ghalib In this lecture The Human ○ Information Processing Model ○ Input/Output channels Human Modeling The Model of Human Processor; Card, Moran and Newell, 1983 The model comprises three subsystems: the perceptual system, handling sensory stimulus from the outside world. the motor system, which controls actions. the cognitive system, which provides the processing needed to connect the two. Human Modeling We will use the analogy of the user as an information processing system - Input–Output, - Memory and - Processing unlike the computer, it is also influenced by external factors such as the social and organizational environment 5 Human Senses Cones vs Rods 120 million are rods vs 6 million are cones 3–4% of the fovea is occupied by cones which are sensitive to blue light  Cones vs Rods Cones provide the vision in the bright light (daylight) while rods provide the vision in the dim light (night). Rods are located near the periphery of the retina, whereas cones are present in the center of the retina. Lack of rods can cause night blindness while lack or deficiency cones can result in the color blindness (8% of males & 1% of females suffer from color blindness). Rods and Cones Peripheral Vision Visual Field - Vision and Eye Health Peripheral Vision Drives User Attention Peripheral Vision Fix on the dot in the center The letters should be equally readable Peripheral Vision Design Choices So if you want a user to see an error message at the bottom of the screen it had better be flashing. Moving fancy impressive icons will be distracting the attention even when the user is not looking directly at them. Visual Perception Perception: The way you think about or understand someone of something. “We don’t see things as they are, we see them as we are.” -- Anais Nin Role of size constancy in perception Perceiving Size and Depth The Law of Size Constancy Perceiving Size and Depth The Cue of Familiarity Perceiving Size and Depth The Cue of Overlapping Perceiving Brightness Luminance is the amount of light emitted by an object In dim lighting, the rods predominate vision. Since there are fewer rods on the fovea, objects in low lighting can be seen less easily when fixated upon, and are more visible in peripheral vision. Visual acuity increases with increased luminance. - As luminance increases, flicker also increases. The eye will perceive a light switched on and off rapidly as constantly on. - Flicker is also more noticeable in peripheral vision. The larger display, the more flicker we notice. Perceiving Color Hue: the spectral wavelength of the light. Intensity/Value: the brightness of the color Saturation: is the amount of whiteness in the color Perceiving Color Perceiving Color 3–4% of the fovea is occupied by cones which are sensitive to blue light Color vision is best in the fovea, and worst at the periphery with more rods Perceiving Patterns Perceiving Patterns Perceiving Patterns Perceiving Patterns Perceiving Patterns Perceiving Patterns Law of Proximity Perceiving Patterns Law of Similarity Perceiving Patterns Design Choice: Where is the middle We tend to see the center of a page as being a little above the actual center. In graphic design this is known as the optical center – and bottom page margins tend to be increased by 50% to compensate. Reading Adults read approximately 250 words a minute. It is unlikely that words are scanned serially, character by character. Experiments have shown that words can be recognized as quickly as single characters. Familiar words are recognized using word shape. Reading Design Choices Removing the word shape clues (for example, by capitalizing words) reduces the reading speed and accuracy Experiments have shown that standard font sizes of 9 to 12 points are equally legible Reading from a computer screen is slower than from a book (longer line length, fewer words to a page, familiarity of the medium of the page) A negative contrast (dark characters on a light screen) provides higher luminance and, therefore, increased acuity, but more flicker! Human Ear 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 The human ear can hear frequencies from about 20 Hz to 15 kHz We can also identify a sound’s location, since the two ears receive slightly different sounds Sound Components ○ Pitch is the sound frequency ○ loudness is the amplitude ○ Timbre: type or quality Cocktail Party Effect Interface Design Attention – to attract the user’s attention to a critical situation or to the end of a process. Status information – continuous background sounds can be used to convey status information. For example, monitoring the progress of a process. Confirmation – a sound associated with an action to confirm that the action has been carried out. For example, associating a sound with deleting a file. Navigation – using changing sound to indicate where the user is in a system. For example, what about sound to support navigation in hypertext? Touch Touch provides us with vital information about our environment. Less important than vision and hearing. To understand its importance: See the users of virtual reality games: they can see the computer-generated objects which they need to manipulate but they have no physical sensation of touching them! Why people prefer online shopping for tickets, books and food, but not for clothes? Feeling buttons depression. Human Skin Stimulus received via receptors in the skin: Thermoreceptors – heat and cold Nociceptors – pain Mechanoreceptors – pressure ○ Rapidly adapting mechanoreceptors (RA) ○ Slowly adapting mechanoreceptors (SA) Two-point threshold test Response - Reaction A person can react to an A visual signal in 200 ms, Auditory signal in 150 ms, and Pain in 700 ms Combination of signals produce faster response Practice improves reaction time Response - Accuracy Is whether speed of reaction results in reduced accuracy? Answer: not always Movement Speed Movement time = a + b log(distance/size + 1) -- Fitts’ Law References - Chapter 1, The human, “Human-Computer Interaction”, 3rd edition - Cutaneous somatosensory receptors in mammals https://www.nature.com/articles/nrn2993/figures/1 Homework Reading - Chapter 1, The human, “Human-Computer Interaction”, 3rd edition - Section 1.1 - Section 1.2 Exercise - Is this design for menus better than the standard one?