Visual Perception

Question 1

Principle of visual perception 7 steps

Answer 1

Environmental stimulus 
Light if reflected and transformed 
Receptor processes 
Neural processing 
Perception recognition
Action

Question 2

The dorsal pathway

Answer 2

The dorsal pathway is extending to the posterior parietal cortex and is thought to be involved in motion, depth and spatial information.

Dorsal pathway is multifunctional, attention, eye movements, numerical calculation and spatial processing.

Question 3

The ventral pathway

Answer 3

The ventral pathway is extended to the inferior temporal cortex and is more concerned with form and colour.

Visual areas may also be involved in higher cognitive functions such as working memory and visual imagery.

Anterior regions of the Fusiform gyrus contain brain regions important in word and object recognition.

Question 4

Object recognition

Answer 4

Mathematical analysis of the luminance structure in 2D images provides information about the structure of surface of objects in 3D space.

This approach was developed by David Marr from the Massachusetts institute of technology.

Question 5

Helmholtz’s theory of unconscious inference

Answer 5

We perceive the object that is most likely to have caused the proximal stimulus.

Our perceptions are the result of unconscious inferences.

This inference happens rapidly and unconsciously

Solving problem approach - observers knowledge of the environment

Question 6

Regularities in the environment

Physical regularities

Answer 6

Regularly occurring physical properties of the environment.

More vertical and horizontal orientations

Light from above assumption

Question 7

Semantic regularities

Answer 7

Semantic regularities are the characteristics associated out in different types of scenes

Question 8

A scene Schema

Answer 8

Is the knowledge of what a given scene ordinarily contains ( expectations of what you’d expect to find/ see)

Question 9

The Bayesian inferences (Reverend Thomas Bayes (1702-1761)

Answer 9

The estimation of the probability of a given outcome is influenced by two factors.

The prior probability

The likelihood of a given outcome

Question 10

Experience dependent plasticity

Answer 10

Theory of natural selection - characteristics that enhance survival chances are passed to the next generation.

Neurones are tuned to respond best ti what we commonly experience.

Learning brains functioning can be tuned to operate best in through specific environment through the experience dependent plasticity.

Question 11

Inverse projection problem

Answer 11

Priors (knowledge)

Likelihood - additional information from retinal image and distance perception.

Changing the viewing angle

These processes occur rapidly and unconsciously

The retinal image is the starting point

Bayesian inference restate Helmholtz idea

Research used Bayesian inference to develop computer vision systems that can apply knowledge about the environment.

Question 12

Kurt Koffka (1886- 1941) Wolfganger Kohler (1887-1967) Max Wertheimer (1880-1943)

Answer 12

Gestalt = whole for (holism)

In reaction to structuralism

Perception is not out of local sensory atoms by simple concatenation

Whole is different from sum of parts

Question 13

Pragnanz Principle = digital goodness

Answer 13

Aspect of the perceptual experience that is a composition of simplicity, order and regularity of and object.

Many different perceptions are possible, figurative goodness determine which one is perceived

Good figures more accurately than bad ones

Question 14

Perceptual grouping: Law of

Answer 14

Proximity- close objects tend to be grouped together

Continuity- organising images to make smooth continuity rather than abrupt changes

Similarity- similar objects tend to be grouped together

Common fate - objects that move in the same way tend to be grouped together

Closure - whole shape perceived by filling gap where info is missing

Symmetry- objects tend to be grouped together to form combined symmetrical object

Question 15

New principles of perceptual grouping

Answer 15

Synchrony - visual events that happen at the same time tend to be perceived together

Common region

Element connectedness

Question 16

Figure - ground segregation

Answer 16

Figure perceived as having distinct form. Bring in front of ground and having contours, ground perceived as lacking form.

Question 17

Strengths of Gestalts Law of Perceptual Organiser

Answer 17

It is of fundamental importance to understand the processes of perceptual organisation

Nearly all laws of grouping have stood the test of time

The notion that observers perceive the simplest possible organisation of the visual environment is very fruitful (Law of Pragnanz)

Question 18

Limitations of gestalt laws of perceptual organiser

Answer 18

Too much ignorance of the experience and learning in determining perceptual grouping and figure ground segregation,

focuses on the processes intrinsic to the perceiver disconnected from the environment.

Mostly descriptive but lack of adequate explanation.

Gestalts law applies to 2D drawings and not 3D real objects.

Question 19

Colour constancy - perception of colour is relatively constant despite changing light sources

Answer 19

Sunlight has approximately equal amounts of energy at all visible wavelengths.

Tungsten lighting has more energy in the long wavelengths

Objects reflect different wavelengths from these two sources.

The light reflected from objects changes as the illuminant changes, from Wandel (1995)

Question 20

Mechanisms of colour constancy

Answer 20

Chromatic adaptation occurs when exposed to chromatic colour leads to receptors:

• Adapting when the stimulus colour selectively bleached a specific cone pigment.

Decreasing in sensitivity to the colour

White balance: adaptation occurs to light sources leading to colour constancy.

Question 21

Experiment by uchikawa et al (1989)

Answer 21

Observers show sheets of coloured paper in three conditions.

Baseline: paper and observer in white light

Observer not adapted: paper illuminated by red light; observer by white.

Observer adapted: paper and observer on red light.

Question 22

Results

Answer 22

Baseline: under white light green paper is seen as green

Observer not adapted - perception of green paper is shifted toward red

No colour consistency in this condition

Observed adapted: perception of green paper is slightly shifted towards red.

Partial colour constancy was shown in this condition