Perception Flashcards
some facts
- more sharp in the middle of the focus
- objects nearer than 25 cm are difficult to focus
- constant near-focusing leads to fatigue
- blind spot about 15-20° from the optical axis in your eye - objects there are not seen directly but “recomputed”
- maximum sampling frequency for images of about 22 img/sec
- Humas are very sensitive to movement outside of about 30° of the main focus - but are able to ignore it (tunnel effect)
focus areas
Foveal area: 1-2°
Para-foveal area: 2-5°
Peripheral area: 6-220°
Reading Distance
- handy, tablet: 40cm
- watch: 50cm
- computer monitor: 55-60 cm
Presbyopia
Altersweitsichtigkeit
happens to everybody and is unavoidable
avoid near point reading in general!
visual perception
is the process of extracting meaning from sensory information. It is concerned with recognition and understanding.
Vision
Vision is an easier process (compared to visual perception) concerned with detecting color, shapes or edges of objects. Vision does not necessarily require an understanding of the world surrounding us.
Gestalt Laws
The Gestaltists, a group of psychologists, identified a number of properties that can be regarded as innate to all humans. Thus, their findings are called Gestalt Laws.
Gestalt Laws are methods that the brain uses to simplify recognition by ordering them
- proximity
- continuity / common fate
- closure
- part-whole relationships
- similarity
- symmetry
Gestalt - proximity
Objects that are close i space ore time tend to be perceived together
can be used e.g. for UI arrangement of buttons or information
Gestalt - common fate
Objects that “move” together are seen as related
Gestalt - Prägnanz, law of good gestalt
unknown figures are automatically separated into known simple forms
Gestalt - closure
We tend to see things as complete objects even though there may be gaps in the shape of the objects
closed figures are perceived more easily than incomplete or open figures
Gestalt - continuity
We tend to perceive sooth, continuous patterns instead of disjoint, interrupted patterns
Gestalt - similarity
Similar figures tend to be grouped together
Gestalt - the area principle
Objects with small area tend to be seen as the figure, not the ground
(the smallness principle)
Gestalt - Surroundedness Principle
An area that is surrounded will be seen as the figure and the area that surrounds it will be seen as the ground
Stimulus Intensity
We respond first to the intensity of a stimulus and only then do we begin to process its meaning
Proportion
Proportion can be used to represent logical hierarchies (Überschriftgrößen)
seen as aesthetic:
- golden ration
- fibonnaci …
Screen complexity
measure of complexity. can be used to calculate the relative complexity, and therefore the difficulty, of the design
To measure the complexity for a particular screen:
- place rectangle around every screen element
- count the number of elements and the number of columns (vertical alignment points)
- count the number of elements and the number of row (horizontal alignment points)
Complexity vs usability
both overly simple and overly complex screens are low in usability
three components:
- effectiveness
- learnability
- attitude
Depth Perception
The arrangement of our visual sensors (eyes) allows us to perceive our world three-dimensionally
- primary depth cues: relevant e.g. to immersive virtual reality systems
- secondary depth cues: more relevant e.g. to non-immersive applications such as games
Primary Depth Cues
retinal disparity:
* as our eyes are approximately 7cm apart, each retina receives a slightly different image of the world. This is processed by the brain and interpreted as distance information
stereopsis:
* Stereopsis is the process by which the different images of the world received by each eye are combined to produce a single three-dimensional experience
accommodation:
* this is a muscular process by which we change the shape of the lens in our eyes in order to create a sharply focused image. The information from the muscles is unconsciously used for depth information.
convergence:
Over distance of 2-7 meters we move our eyes more and more inwards to focus on an object at these distances. This process is used to provide additional depth information.
Secondary Depth Cues
secondary depth cues are the basis for depth perception on two-dimentional displays.
Cues:
- light and shade
- linear perspective: e.g. shadow on an arrow
- height in the horizontal plan
- motion parallax: e.g. when riding on a train and looking out of the window, near objects flash by quickly, objects further way slower
- overlap: e.g. overlapping windows in a GUI
- relative size: see sun + cloud
- texture gradient: textured surfaces appear closer
colors - problem with displays
information displayed with additive active light might not be as natural as reflected light
- humans are not used to looking “into” the light
- natural perception is reflected light
additive coloured information presentation should be embedded into an environment that has equal brightness to avoid fatigue
color - visual limitations
- blue is on the edge of the spectrum. Avoid using it for small and tiny elements
- the ability to distinguish color is directly related to he size of an object
- shapes are identified by their edges. Edges are faster identified by lins than by colours
- better colour perception in the middle of the focus
- about 8% of men (0.4% of women) have deficiencies to perceive colors correctly. Most deficiency is detection of green
Colours may cause emotional response
emotional response varies from culture to culture
people from different age and sex have different preferences (e.g. children prefer colourful objects)
industries, professional communities, corporate have their own colour connotations
Color coding
can improve recall, search-and-locate tasks, decision judgements : overall performance
does not replace a good structure!
differences to distinguish color variations vary between colors, individuals and cultures
targets may use highly divers colors from those of their surroundings
optimal colors
avoid any incompatible color combination
background to foreground contrast is also important
use max 4 colors on screen with max 4 variants each
sound
loudness
- expressed in decibel (dB)
- dB is logarithmic scale (40dB is 10 times louder than 30dB)
- whisper: 15dB
- normal conversation: 60dB
- car horn: 110 dB
- rock concert: 120+ dB
Frequency range of hearing: 20Hertz - 20kHz
4 stages of auditory perception
Transduction
* translation of sound vibrations into neural impulses
Auditory grouping
- segregation into separate streams
- integration of sound in coherent streams
Scene Analysis
Interpretation
Audio User Interfaces
Vision and Hearing go together
Audio can tell your eyes where to look
Audio can perceive faster than visual cues
Audio is transitory! Vision is often not
