Perception: vision Flashcards
Define sensation
The passive process of bringing information from the outside world into the body and the brain
Define perception
The active process of selecting, organising, and interpreting the information brought to the brain by the senses
Describe the organ brain structure association
Sense organ (eye) -> (arrows are electrical signals) receptor cells (rods and cones) –> nerve conduit (optic nerve) –> brain area (visual cortex)
What are the two approaches to study perception?
Gestalt psychology and computational approach; feature representaiton
What is gestalt psychology
Gestalt - german for form of shape
Paradigm which emerged in late 19th century
Concerned with identifying laws which govern visual perception
What are gestalt laws
Explains how parts are arranged into forms and object and perceived as a whole
What is an issue with gestalt psychology?
It is descriptive not mechanistic because a major focus of gestalt laws is describing the conditions that lead to grouping. Gestalt is less about understanding the mechanism underlying grouping
What is the gestalt law of similarity?
Elements that look similar will be perceived as being part of the same form
What is the gestalt law of proximity?
Elements that are close together will be perceived as belonging together
What is the gestalt law of Good continuation?
We perceive lines as following a smooth course
What is the gestalt law of closure?
A boundary isn’t necessary for us to perceive a shape. When small elements are arranged in groups, we tend to perceive them as larger figures. This can lead us to seeing illusory lines that do not exist.
What is the gestalt law of Pragnanz (Similarity)?
We organise a scene according to its simplest (shortest) explanation
What is the gestalt law of common fate?
Elements that move together tend to be grouped together
What is the gestalt law of symmetry?
Elements that are symmetrical tend to be grouped together
What is the gestalt law of parallelism?
Elements that are parallel tend to be grouped together
What is feature representation in the visual pathway?
Eye-rods and cones-optic nerves-visual cortex
What is the visual pathway?
1) retina
2) optic nerve
3) thalamus
4) primary visual striate cortext V1
5) High visual cortices V2 IT
Describe feature representation in the optic nerve and thalamus
Receptive fields - features that neurons are most responsive too
- centre surround organisation
- light centre and dark surround or vice versa
- neurons responsive to dot like circular visual stimuli
Describe feature representation in the primary visual cortex
- Classic studies by Hubel and Wiesel in 1950s investigating primary visual cortex
Neurons in V1 respond to circular stimuli but are not very active
Instead they are excited by line stimuli of specific orientation
What is orientation important for
Edge detection
What are receptive fields in V1 built up by
Combining receptive fields of neurons in the thalamus
What are the two streams of visual processing?
The WHAT pathway and the WHERE pathway
Describe the WHAT pathway
Identifies shape and objects, ventral to inferior temporal lobe , VENTRAL STREAM
What is the WHERE pathway?
Motion, dorsal to superior parietal lobe, DORSAL STREAM
Describe computational thinking
We reconstruct a visual scene by combining simpler elements, faithful reconstruction, built from visual inputs alone
Describe how we think using gestalt psychology?
We combine elements in ways to gain a holistic understanding of a scene, simplified interpretation, built using assumptions and knowledge bout the world
What is top down?
Background knowledge and expectations influence what is perceived. Expectation driven
What is bottom up?
Processing the stimuli influences what is perceived - data driven
Describe top down information
Context matters - our environment gives us clues when the stimulus is ambiguous. The context we perceive a stimulus in can cahnge our perception of it
What are visual illusions a consequence of?
Bottom up vs top down processing
How do we resolve ambiguities?
We need to decide which visual scene caused the image on the retina. Assumptions and cues are combined to make a best guess at what it is we’re seeing.
Cues; features of the image that give clues as to the nature of the stimulus (BU)
Assumptions; expectations about what we will see or what different cues mean (TD)
