4. Basics Of Visual Processing Flashcards
Objectivist view of vision
Perception reflects reality. An appealing idea, but incorrect.
Subjectivist view of vision
We perceive via inference.
Why is inference necessary?
Vision is your brain’s best guess / a story your brain tells you, based on assumptions and use of noisy, incomplete evidence.
What is phenomenology?
Applying physics to make subjective predictions about perception.
What is psychophysics?
Objective and quantifiable measure of the relationship between visual stimuli and behaviour.
Psychophysics is agnostic about _____________
__________________ about the processes that happen between stimuli and related behaviour.
Two perception based ways of studying vision
Phenomenology and psychophysics
Four hardware based ways of studying vision
Neuropsychology / brain imaging Stimulation / implants Physiology Anatomy
Studying hardware helps us to find out what happens between ____________ and ____________
Studying ___________ helps us to find out what happens between stimulus and behaviour
What can we find out from neuropsychology studies, like brain imaging or lesion cases?
Where is the system? (What kind of study would test this?)
What can we find out from stimulation / implant studies, like cortical implants for people with complete blindness?
Where is the system, and what does it do? (What kind of study would test this?)
What can we find out from physiology studies, like measuring the voltage of a cell with electrodes?
What do its components do? (What kind of study would test this?)
What can we find out from anatomy studies, like looking at the dendrites of a neutron?
How are its components organised? (What kind of study would test this?)
How does Marr describe: a) the goal of visual processing b) how we achieve it?
a) discovering from images what is present and where it is, to produce a description useful to the viewer, so that they can behave effectively b) through a hierarchy of increasingly symbolic representations
Retinal ganglion cells are the ____________
The first neurons in the visual pathway
Three types of retinal ganglion cells (RGCs)
Midget Parasol Small bistratified (Are all types of….)
Receptive field
A region of space where if visual info lands on it, it will affect the activity of the cell.
Three properties of retinal ganglion cells receptive fields:
- circular - antagonistic centre-surround organisation (on-centre or off-centre) - confers selectivity for size and polarity (onset/offset) of features
Spontaneous activity
Random baseline firing of cells at rest
How will an on-centre RGC respond to: a) a light spot in the centre b) a light surround
a) a light spot in the centre will stimulate the on response b) a light surround will stimulate the off response What type of cell am I?
How will an off-centre RGC respond to: a) a light spot in the centre b) a light surround
a) a light spot in the centre will stimulate the off response b) a light surround will stimulate the on response What type of cell am I?
How will an on-centre RGC respond to: a) a dark spot in the centre b) a dark surround
a) a dark spot in the centre will stimulate the off response b) a dark surround will stimulate the on response What type of cell am I?
How will an off-centre RGC respond to: a) a dark spot in the centre b) a dark surround
a) a dark spot in the centre will stimulate the on response b) a dark surround will stimulate the off response What type of cell am I?
How will a retinal ganglion cell respond to a uniform field of light?
A ____________ will not respond to a ______________. It responds to change (in space or time) and specificity (size and polarity)
Midget ganglion cells:
a) three features
b) associated pathway
I am:
a) sensitive to colour and fine detail (I have small RFs!) but I have poor temporal sensitivity (poor for motion)
b) associated with the parvocellular pathway What am I?
Parasol ganglion cells:
a) three features
b) associated pathway
I…
a) have no colour sensitivity, see coarse detail (I have large RFS!) and height temporal sensitivity (I’m good with motion!)
b) am associated with the magnocellular pathway What am I?
