How long does a picture need to be available for it to be perceivable?
How many pictures per second are needed to perceive movement? How many are needed to perceive fluid movement?
A picture needs to be available 15 -50 ms to be perceivable.
With 3-5 pictures per second, movement can be perceived.
For fluid movement 20-25 pictures are needed.
When does flickering on a screen occur?
When the refresh rate is between 20 - 70 Hz. To avoid flickering HD TVs use a refresh rate of ~100Hz.
Name the parts of the eye
Name all 8 gestalt laws
proximity: near objects grouped together
similarity: similar objects grouped together
common form: object of similar shape, pattern or colour ... (unterschied zu similarity unklar)
good continuation: spacial and temporal simplicity
common fate: o. moving in same direction grouped together
closure: consures are completed
distinction between inside and outside/ Common region
figure ground segregation
Describe the process of accommodation in the human eye.
The optical principle of refraction describes the bending of light as it passes from one medium to another. Depending on the optical density, the speed of light changes and the light is redirected.
The human eye is made up of a four-lens system (cornea, anterior chamber, lens and vitreous chamber) which uses this principle to focus infalling light onto specific points on the retina. The system can change its refractive power by pulling the lens towards the outer edge and flattening it.
With age the refractive power of the eye will decrease
How do can those eye movements benefit us?
Fixation via saccades; Convergence; Slow pursuit; Fast phases
Fixation via saccades → Allows to scan the environment
Convergence → An inside movement, that helps to get a sharp picture on both eyes while scanning the environment
Slow pursuit → follow moving objects
Fast phases → fixate a point while the own head moves
Which eye movements help us to:
Scan the environment
Get a sharp picture on both eyes while scanning the environment
Fixate a point while the own head moves
Follow moving objects
What can we perceive in different visual fields?
Describe the types of sensitive cells on the retina
The two types of photochemical receptors on the retina are rods and cones.
Rods are highly light-sensitive and are responsible for vision in low-light (scotopic) conditions.
Cones are less light-sensitive and are responsible for color vision and sharp detail in bright light (photopic) conditions. There are thre types of cones for the perception of blue green and red light
There are a lot more rods then cones
Where are the rods and cones concentrated?
The rods are mostly concentrated outside, around the fovea, while the cones are concentrated in the fovea
What is the fucion of ganglion cells?
ÜBERARBEITEN
- 100+ million receptores connected to ~1.6 million Ganglion cells
- Ganglion cells forwarding information to the brain
- space where receptores are connected to ganglion cell is called receptive field
- receptive field of cones is smaller than for rods
receptive field
Between which frequencies can we perceive color?
400 - 700 nm
Why is it possible to see the whole spectrum of colors with only 3 types of cones?
+ gangliones
How large is the light sensitivity range?
Large bandwidth (approx. 10 orders of magnitude)
Which adaptation mechanisms exist to percieve all kinds of light intensities?
Light adaptation mechanisms:
Pupil dilation with iris (change of pupil size)
Adaptation of chemical processes in the photoreceptors (rather slow, ~1h)
Adaptation at the neural level (in-/decreasing amound of neurotransmissions; quicker but less effective)
Which gestalt law is applied here?
Closure: contures are completed
Common form: object of similar shape, pattern or colour ... /
(Ich denke eigentlich similarity)
distinction between inside and outside
What is the Law of good Gestalt?
According to Gestalt psychologists, the fundamental principle of perceptual grouping is the law of Prägnanz, also known as the law of good Gestalt.
The law says that people tend to experience things as regular, orderly, symmetrical, and simple.
-> human perception is biased towards simplicity.
What is the Recognition by components theory?
suggests that objects are recognized by decomposing them into a set of simple, three-dimensional shapes = "geon" (geometric icons).
geons are easily identifiable
geons are arranged to form the overall object.
theory provides a framework for understanding how humans perceive and recognize objects, even when they are partially occluded or viewed from different perspectives.
What kinds of monecular cues exist to perceive depth?
Light and shade: object get illuminated -> shadow on the back
Relative size: more distant objects are smaller in size
Interposition: objects overlaying each other -> overlaying object is closer
Textual gradient: repeated objects seem more fine-grained in the distance
Aerial percpective: more distant objects seem lighter in colour
Perspective: used in pics to create artificial depth
What is motion parallax?
near object seem to move faster than far objects
Why can observers feel unwell after bein exposed too long to a 3D display?
What is deletion and accretion?
object cover each other depending on our position
Which eye movements are important for reading?
saccades: short fast jumpes between fixation of eye
fixation: focus on (for example) text (only ~5 characters can be fixated at a time)
regression: backward jump in eye movement (increases with text complexity)
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