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 the refresh rate is between 20 - 70 Hz. To avoid flickering HD TVs use a refresh rate of ~100Hz.

Eye: Anatomy

Gestalt laws

1. proximity: near objects grouped together

2. similarity: similar objects grouped together

3. common form: object of similar shape, pattern or colour ... (unterschied zu similarity unklar)

4. good continuation: spacial and temporal simplicity

5. common fate: o. moving in same direction grouped together

6. closure: consures are completed

7. distinction between inside and outside/ Common region

8. figure ground segregation

Eye: System

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

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

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

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

The rods are mostly concentrated outside, around the fovea, while the cones are concentrated in the fovea

- 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

Visual Perception

400 - 700 nm

• + gangliones

Light sensitivity

Large bandwidth (approx. 10 orders of magnitude)

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)

Closure: contures are completed

Common form: object of similar shape, pattern or colour ... /

(Ich denke eigentlich similarity)

good continuation: spacial and temporal simplicity

distinction between inside and outside

figure ground segregation

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.

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. 

• 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

near object seem to move faster than far objects

object cover each other depending on our position

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)