Visual Perception Flashcards
Principle of visual perception 7 steps
Environmental stimulus Light if reflected and transformed Receptor processes Neural processing Perception recognition Action
The dorsal pathway
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.
The ventral pathway
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.
Object recognition
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.
Helmholtz’s theory of unconscious inference
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
Regularities in the environment
Physical regularities
Regularly occurring physical properties of the environment.
More vertical and horizontal orientations
Light from above assumption
Semantic regularities
Semantic regularities are the characteristics associated out in different types of scenes
A scene Schema
Is the knowledge of what a given scene ordinarily contains ( expectations of what you’d expect to find/ see)
The Bayesian inferences (Reverend Thomas Bayes (1702-1761)
The estimation of the probability of a given outcome is influenced by two factors.
The prior probability
The likelihood of a given outcome
Experience dependent plasticity
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.
Inverse projection problem
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.
Kurt Koffka (1886- 1941) Wolfganger Kohler (1887-1967) Max Wertheimer (1880-1943)
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
Pragnanz Principle = digital goodness
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
Perceptual grouping: Law of
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
New principles of perceptual grouping
Synchrony - visual events that happen at the same time tend to be perceived together
Common region
Element connectedness
Figure - ground segregation
Figure perceived as having distinct form. Bring in front of ground and having contours, ground perceived as lacking form.
Strengths of Gestalts Law of Perceptual Organiser
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)
Limitations of gestalt laws of perceptual organiser
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.
Colour constancy - perception of colour is relatively constant despite changing light sources
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)
Mechanisms of colour constancy
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.
Experiment by uchikawa et al (1989)
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.
Results
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
