The Information Processing Model A model for understanding human cognition. from: Wickens, Lee, Liu, & Becker (2004) An Introduction to Human Factors Engineering. p. 122 ISE 412

Assumptions in the IP Model Each stage transforms data and takes some time Sensory processing visual, auditory, kinesthetic quality and quantity of input depend on limits of senses Short-term sensory store temporary storage at the sensory channel requires no conscious attention Perceptual encoding stimulus is assigned to single perceptual category (from LTM) levels of complexity of perceptual decisions absolute judgement (1 dimension) loudness of a tone, crowd size pattern recognition (2 or more dimensions) medical diagnosis, Sherlock Holmes ISE 412

Assumptions in the IP Model Stages (cont.) Decision making what to do with perceived information critical point in information processing Memory Working memory (short-term memory) Long-term memory Response execution calling up and releasing necessary muscle commands to perform actions very complex Feedback monitoring the consequences of actions not necessarily conscious ISE 412

Assumptions in the IP Model Stages (cont.) Attention searchlight - which information source to monitor resource of limited availability Model not to be taken literally Implies passivity; where are the goals? Stages not sharply defined; overlap in time Stages are not really "boxes" in the brain Information flow may be right to left; e.g., expectations can influence perceptions ISE 412

The Information Processing Model The traditional driver for research and understanding. A useful organization scheme. ISE 412

Sensory Register, Part I: The Visual Sensory System How we see: "Light (electromagnetic radiation) is collected by the cornea and passes through the anterior chamber, then through the pupil, which is an aperture in the iris diaphragm, to the crystalline lens. The lens focuses the light by changing shape in a process called accommodation. The image passes through the vitreous humor in the posterior chamber and is projected onto the retina. The retina contains two kinds of photo receptors: rods, which are sensitive to dim light, and cones, which are used in bright light and convey color information. The central region of the retina, which provides the best visual acuity, is the fovea, which contains only cones. Information from the photoreceptors passes through the bipolar cells and ganglion cells (cells in the retina) before passing out of the eye via the optic nerve."[1] [1] Coren, S., Ward, L., & Enns, J. (1999). Sensation and perception (5th ed.). Fort Worth :Harcourt Brace, p. 83. ISE 412

The Visual Receptor System (see chapter 4) The lens cornea – protective surface pupil – opens (dilates) in darkness, closes (constricts) in light accomodation: _______________________________ measured in diopters The retina cones: ___________________________ rods: ____________________________ fovea: ___________________________ acuity: ___________________________ scotopic vision: ______________________ photopic vision: ______________________ adaptation: _________________________ Accommodation - the lens changing to focus an image. 1 diopter = accommodation required to view an object at 1 meter. cones: located primarily in the middle region of the retina; better at picking up fine detail (better acuity); better color sensitivity; more sensitive to glare in low light rods: located primarily on the periphery of the retina; more sensitive (better in low light); “color blind”; more sensitive to motion fovea: center of the eye; composed entirely of cones acuity: smallest visual angle that can be detected (see table 4.2, pg 68) scotopic vision: night vision, only rods operating photopic vision: vision when illusion is sufficient to activate both rods and cones (mostly cones) adaptation: the time it takes for rods to regain their sensitivity after exposure to light ISE 412

Example: driving at night Specific hazards caused by: Glare Reduced contrast sensitivity Loss of color vision Particularly bad for older drivers due to: Loss of contrast sensitivity due to age Loss of accomodation Glare is irrelevant light of high intensity. It has the effect of destroying the rod's sensitivity to low spatial frequencies. ISE 412

What affects Visibility? Of print… Good Bad BAD item 1: too small (font size) item 2: too light (contrast) item 3: difficult fonts (e.g., spatial frequency) item 4: polarity (light on dark) – what is “good” depends on environment, lighting, etc. Bad Bad ISE 412

What affects Visibility? Characterizing and Measuring Light Color hue pure wavelength visible spectrum ~400 – 700 nm saturation amount of achromatic light mixed in brightness amplitude Design considerations use color as a secondary source of information design for monochrome first consider simultaneous contrast negative afterimage . Know how to use color in displays. It should be used as a secondary source of information. Design for monochrome first. Simultaneous contrast and negative afterimage affect our perception of color. ISE 412

What affects Visibility? Characterizing and Measuring Light (cont.) Brightness measures (review) luminous intensity, luminous flux energy at the source, candela illuminance amount of energy striking an object, lux or foot-candles (fc) luminance amount of energy reflected from an object, foot-lambert (FL) reflectance ratio of the amount of light striking the object to the light reflected from the object, illuminance luminance ISE 412

What affects Visibility? Characteristics of Visual Displays Visual angle, VA = tan-1(H/D) VA = 3438H/D min Example: reading ‘Good’ text from your notes page, H = ______ D = ______ VA = ___________________________ For example, H = 0.25 in D = 18 in VA = tan-1(H/D) = tan-1(0.25/18) = 0.7957° = 47.74 min. ISE 412

What affects Visibility? Characteristics of Visual Displays (cont.) Contrast, Luminance of light areas, LL Luminance of dark areas, LD Contrast = Spatial frequency cycles of light and dark per degree of VA Polarity dark on light vs light on dark (LL – LD) (LL + LD) ISE 412

What affects Visibility? Characteristics of Observers Visual Acuity Age Contrast sensitivity Night vision Characteristics of Environment Ambient light e.g., daylight vs night, glare, etc. Movement Distractions ISE 412

Your turn … Define system requirements for your project based on this understanding of the visual sensory system. Typical statements could include: The system must accommodate ____________________. The system should allow for _______________________. The system should include mechanisms that will _____________________. Be careful not to start designing yet! ISE 412