Perception Flashcards
(19 cards)
Describe the eye
The retina: thin, light-sensitive membrane located at the back of the eye, contains photoreceptors for vision (i.e. rods and cones)
Fovea: Small area of the retina, high density of cones, our central vision.
The lens: behind the pupil, actively focuses or bends light as it enters the eye so it falls on the fovea.
What is the difference between central and peripheral vision?
Central vision:
- Also referred to as foveal vision
- The centre of the visual field - the size of a thumbnail when extending your arm
- Mainly constructed from cones (sensitive to different light frequencies)
- Good colour-vision
- 6-7 million retinal cone cells in each eye, connect 1:1 to ganglion neuron cells, 1% of the retina, the brain’s visual cortex devotes around 50% of its area to processing foveal input
- High acuity vision
- Often associated with goal-directed attention
Peripheral vision:
- Mainly constructed from rods (sensitive to overall brightness)
- Poorly lighted environments (night vision)
- Low acuity
- Poor colour vision: We get the impression that our peripheral vision perceives colour but that is because peripheral vision is driven by top-down processing so we see what we expect to see
- Reacts to motion (drives our attention and visual search)
- Often associated with bottom-up (stimulis-driven) attention
How does the brain see colours?
The brain (neurons in visual cortex) applies subtraction to the signals coming from the optic nerves.
Three cone types: correspond to short (blue), medium (green) or long (red) wavelengths of light. Combination of activation of the cone types that give us colour vision.
Our colour vision works in pairs and oppose one another. Three colour-opponent channels:
a. A red-green opponent channell: responds to red stimuli and inhibits green stimuli or vice versa.
b. A yellow-blue opponent channels: responds to yellow stimuli and inhibits blue or vice versa.
c. A black-white opponent channel (overall luminance):
What does colour blindness entail, how many does it affect, and what are solutions for design?
What: Difficulty distinguishing between certain pairs of colour (mostly red-green).
Obs. colour blindness does not mean total inability to see colours, it just means that the sensitivity of cone cells overlap abnormally. This might lead to confusion of colour hues, e.g. red and green.
8% of men and 0.5% of women are colour blind.
Solutions for design
- Avoid colour pairs that colour-blind can’t distinguish: dark red vs. dark green, dark red vs. black, blue vs. purple, light green vs. white
- Don’t use dark reds, blues or violets against any dark colour. Instead, use dark reds, blues and violets against light yellow and green
- Use a colour blindness filter that simulates how the design would look to a person who is colour blind
What is the principle of proximity and how can it be used in design?
“Objects near each other appear grouped, while those far apart do not”
Applies even when the objects are not alike. Typically the strongest principle, can overrule other principles.
Place related elements close to each other
Spaces between objects that are not related
Note! Boxes of lines to make sure things appear separate is often not necessary due to this principle
What is the principle of similarity and how can it be used in design?
“Similar looking objects appear grouped, all other things being equal”
Not only do we perceive objects as belonging together, we also often believe that they relate in function
Similarity by shapes, sizes, colour and orientation.
Often colour > size > shape
What is the principle of continuity and how can it be used in design?
“When visual elements are aligned with each other, our visual perception is biased to perceive as continuous forms rather than disconnected segments”
Examples: Scalers (e.g. sound on Mac), progress bars, e.g. two lines crossing
What is the principle of closure and how can it be used in design?
Our visual system automatically tries to fill in missing information to perceive incomplete, open figures as complete, whole objects rather than separate pieces.
Examples: Half an app icon in a scroll window, icons and logos, can be used to reduce attentional clutter since you don’t need full figures
What is the principle of symmetry?
“Elements that are symmetrical to each other tend to be perceived as a unified group”
Simplifies our perception. More an aesthetic choice. While on the one hand it indicates grouping, if there is just one asymmetrical part of an otherwise symmetrical design, it will draw your attention a lot
Less important principle according to Marc
What is the principle of figure/ground and how can it be used in design?
“Our mind separates the visual field in the figure (the object of focus, the foreground) and the ground (background)”
Makes us see depth in the visual scene, gives a 3D perspective of the 2D visual input.
Can be used in design to communicate to the user what the important features are and what can be ignored.
Examples: Pop-up information, contrasting colour, shapes or textures to make something stand out boxes and shadows, e.g. the window on Mac with calculator, internet, brightness etc. that is placed in front of the background
What is the principle of common fate and how can it be used in design?
“Objects that move together are perceived as grouped or related”
Can override other principles.
The objects should move in synchrony, i.e. same speed, same time and in the same direction.
Can be used in design to overrule other principles to show relatedness of objects.
What are two main points regarding visual hierarchy?
- User’s don’t read on interfaces, they scan for things relevant to their goals.
- When we see an interface, most of the design falls under our peripheral vision and therefore we should design to support the peripheral vision.
What are design solutions for improving visual hierarchy?
a. Minimise the need for users to read: not all uppercase, minimise jargon, use laymen terms as we are not trained in reading those things
b. Make visual hierarchies: make texts scannable by highlighting key words, using meaningful sub-headings, bulleted lists, one idea per paragraph, half the word count than conventional writing, start with conclusion
c. The squint test / apply the blur filter: simulates what our peripheral vision sees
What are the two scanning patterns in Western countries?
The Z-pattern of the F-pattern
What is visual habituation?
Users are more drawn by what they expect to see rather than what they actually see.
What does discriminability of colours depend on+
Paleness, colour patch size and separation space
What is our vision optimised to detect?
Contrasts, edges and rapid changes, not absolute brightness level
What is the visible spectrum of light?
Typically, the human eye can detect wavelengths from around 400 (violet) to 700 (deep red) nanometers.
What are the Gestalt principles?
A set of visual organisation principles. Explain how the human visual system perceives and groups visual elements together to create larger objects.
Originated in the 1920s in Austria and Germany.
