Lectures 2-4
What is light?
Electromagnetic radiation that is part of the electromagnetic spectrum
Both a particle and a wave
Name the two photoreceptors
Rods and cones
What does contralateral mean with respect to vision?
Each hemisphere of the brain responds to the opposite side of the visual field
Describe the 2 core issues our visual system needs to solve to resolve ambiguity
1. Many different objects can generate the same image on the retina
And on the flip side:
2. The same object can generate very different images on the retina
What is color?
How our brain interprets different wavelengths of visible light
________: difficulty seeing close objects
________: difficulty seeing distant objects
_Hyperopia_: difficulty seeing close objects
_Myopia_: difficulty seeing distant objects
For seeing in the dark, when do we rely on cones, and when do we rely on rods?
What part of our visual field has better dark vision early on vs later on?
After the light dims:
Cones: 0-10 mins
Rods: 10-30+ mins
The center of our visual field is better at dark vision earlier, whereas the periphery is better later
The dorsal stream processes __________
The ventral stream processes ___________
The dorsal stream processes spatial and action-related information--the "where" stream
The ventral stream processes object information--the "what" stream
Describe the 2 competing theories of how we resolve ambiguity
•Structuralism: our perception results from just the adding up of visual information. The whole is the sum of its parts; we don’t make any inferences beyond what we see
•Gestalt psychology: the whole is different than the sum of its parts. We “add something” to the basic visual information to create our perception
Describe the two types of attention
•Overt attention: when you move your eyes to a location and attend to that location
•Covert attention: When you shift your attention without moving your eyes
List 3 bottom-up influences on the perceptual process
Salient information
Motion
Changes and abrupt onsets
Powerful stimuli
__________ allow photoreceptors to send signals to each other.
__________ allow ganglion cells to send signals to each other.
___Horizontal cells__ allow photoreceptors to send signals to each other.
__Amacrine cells___ allow ganglion cells to send signals to each other.
Name 4 steps of the path of the visual signal after it leaves the eye, in the correct order
Optic nerve
Optic chiasm
Thalamus (most of the signal)*
Area V1
Ventral and dorsal streams
What is scene gist?
What does it imply for theories of how we analyze scenes?
Scene gist: the general description or basic properties of a scene. typically includes information about:
•The scene category
•What the scene is generally about (its meaning)
•The general layout and spatial structure
Implies that scene recognition does not depend on object recognition
Describe the different components of eye movements, what they form when considered together, and how they are measured
•Fixation: when your eyes stop and take in information
•Saccade: moving your eyes from one place to another
Together, they form a scanpath: the series of fixations and saccades one makes on a given stimulus
Eye movements are measured using eyetracking
Name 2 eye conditions and their corresponding part of the eye
Glaucoma - aqueous humor
Astigmatism - Cornea
Cataracts - Lens
Myopia (nearsightedness) / hyperopia (farsightedness): lens
(Acanthamoeba - cornea)
Later lectures:
Diabetic retinopathy (floaters caused by retina damage)
Macular degeneration - center of the retina (aka macula, which includes the fovea)
Retinal detachment - caused by injury to the retina
What is neural convergence? How does it affect vision?
Neural convergence: one ganglion cell represents many photoreceptors
It compresses vision and makes it lower resolution
What area processes faces?
What disorder results from damage to this area?
How do we process faces?
Fusiform face area
Prosopagnosia
Holistically (processed as a whole, not a collection of features)
Describe 4 gestalt principles
- Good continuation: figures with edges that are smooth are more likely seen as continuous than edges that have abrupt or sharp angles. Also, objects that are partially covered by other objects are seen as continuing behind the covering object
- Pragnanz: (principle of simplicity): Things are seen in a way such that the resulting structure is as simple as possible
- Common fate: Things that are moving in the same direction appear to be grouped together
- Common region: Elements within the same region of space appear to be grouped together
- Uniform connectedness: A connected region of the same visual properties is perceived as a single unit
Describe spatial neglect and the circumstances in which we can overcome it
•Spatial neglect: a neurological condition that causes one to ignore part of the world (Hemispatial neglect: ignoring the left or right half of the world)
•Threatening things can make them notice neglected side, especially when there is less competition from good side
Name the steps of the perceptual process, in the correct order
Distal stimulus, proximal stimulus, receptor processes, neural processing, perception, recognition, action
If a light is shined on a visual receptor, what happens to nearby receptors?
What is this phenomenon called?
If a light is shined on a visual receptor, nearby receptors decrease firing.
This is called lateral inhibition
According to the retinotopic map, if objects are close together in your visual field: _________________________
What does cortical magnification refer to?
The neurons that represent them are close together in Area V1
Cortical magnification: Information in foveal vision is way over-represented in terms of how much space it takes up on the retinotopic map
Describe the 3 components of Bayesian inference, and the goal of Bayesian inference in visual perception
Components:
1. Prior: our initial estimate of the probability of an outcome (pre-existing beliefs/knowledge)
2. Likelihood: the extent to which the current available evidence is consistent with an outcome (current evidence)
3. Inference: The result of combining the prior and the likelihood; what we infer
Goal: resolve ambiguity in what we're looking at
Describe the two mechanisms for color vision (one at the retina, one in the brain)
•Trichromacy: there are 3 types of cones that each prefer different wavelengths: S cones (short wavelengths), M cones (medium wavelengths), L cones (long wavelengths)
•Opponent process theory: color vision is caused by opposing responses generated by blue vs yellow, and red vs green (and white vs black)