L3 - Spatial Vision Flashcards
What is Spatial Vision?
How you see things in space.
What are the things you see in space around you.
Who was David Marr? What did he publish?
Trained as an electrophysiologist and a computer scientist.
Published a book called ‘Vision’ (1980)
What were the 3 stages of vision that Marr suggests that we see vision?
Primal Sketch: Sparse Representation of local features
2.5D Sketch: Shape Representation
3D Sketch: Object Representation
What is a Receptive Field?
The particular region of the sensory space (e.g. body surface, or visual field) in which a stimulus will modify the firing of that neuron.
When you present information the neuron changes its firing rate
What happens to receptor fields (area over which neuron changes its firing rate) as they go ‘up’ the visual systems?
These get bigger as they go up cortex.
By the time they go up to the highest level of cortex they are up to a quarter of your visual field
What is a Primal sketch according to Marr?
You just have little bits of the object, a couple of contours. Not the full outline of a shape just sparse parts.
What is a 2.5D sketch according to Marr?
It’s a representation that suggests that there is a contour that can do something but you do not yet have the whole object.
Not fully formed
What is a 3D sketch according to Marr?
When you put all the contours together you get a whole object and it is fully formed.
Describe Hubel and Wiesel’s Simple Cells.
They are orientation selective.
Have an elongated retinal receptive field containing excitatory and inhibitory zones.
Describe Hubel and Wiesel’s Complex Cells.
They have a relatively large receptive field.
Does not contain identifiable excitatory or inhibitory zones.
It is orientation selective (not as much as simple cells)
What is information that increases the firing rate of a neuron called?
Excitatory
What is information that decreases the firing rate of a neuron called?
Inhibitory
What does elongated mean?
To make (something) longer, especially unusually so in relation to its width.
Does the orientation of a stimulus matter more for simple cells or complex cells?
Simple cells react differently to different orientation whereas complex cells generally don’t.
The lines indicate activation and at what time.
Are human being equally sensitive to all contrasts?
No.
As the background changes it makes it more difficult to see differences in contrast.
- What is Spatial Frequency?
- What is Spatial-Frequency Theory?
- The spatial frequency is expressed as the number of cycles per degree of visual angle.
- That the visual cortex operates on a code of spatial frequency.
Is the peak sensitivity for human contrast at a high, low or mid-range frequency?
Our peak sensitivity is at a mid-range of spatial frequency.
What are the 4 principles of Gestalt Laws?
They argued that we use -
Proximity
Similarity
Common fate
Good Continuation
In order to help organise information
What is Gestalt’s Law of Proximity?
We use proximity to group things together.
If there are 6 dots and 3 are close to one another, we will group those 3 each into individual groups.
What is Gestalt’s Law of Similarity?
When separating objects into groups we typically group objects that are similar to one another together.
What is Gestalt’s Law of Good Continuation?
Parts that flow together neatly (have continuous edges) are typically grouped together.
Boundary is likely to be a smooth contour.
What is Object Invariance?
Humans are able to recognise something as the same type of object, even though the individual items have different attributes.
- You can see something is a bird even if you’ve never seen that type of bird before*
- Some sort of flexible template?*
Describe Haushofer and Kanwisher’s theory of Object Recognition.
There is a specialised region within the brain for distinct categories.
Different areas for faces, houses etc.
Describe Habak, Wilkinson, Zakher and Wilson’s theory on Object Recognition.
It is a bottom-up process that can be thought of in terms of spatial filtering.
Low-level vision, we are constantly doing spatial frequency analysis.
What does the Face Adaptation theory suggest?
That humans have a special ‘face space’ in the brain - the fusiform face area (FFA) that is specialized for facial recognition.
Children can identify faces in objects from a very young age.
True or False
True
We seem to have innate ability to detect faces from a very young age (biological advantage perhaps)
Human beings are just as good at recognizing bits of a face as we are at recognizing a whole face
True or False
False
We struggle to recognize parts of a face and put it to a person.
If you look at an angry face then look at a neutral face you are more likely to perceive the face as a -
Neutral Face
Happy Face
or Angry Face?
Angry Face, it seems as though our interpretation follows over somehow.
Prosopagnosia is?
How is it acquired?
The inability to recognise faces.
Through brain trauma, stroke or degenerative disease. Can be congenital.
Capgras syndrome is?
How is it acquired?
Inability to recognise the identity of a person.
Acquired as a result of brain trauma, stroke or degenerative disease. Can be congenital.
