Chapter 3 + 4: Neural processing and Bottom-up perception Flashcards
What’s the basis of bottom-up perception?
- Basic sensory elements and stimuli are combined, and those combinations are then combined, to eventually produce a perception of the whole.
TRUE OR FALSE: Pattern recognition occurs within the brain
- This is true
- Ex. Rods and cones work independently of one another, but it’s up to the brain to integrate the various signals together to be able to identify patterns
What’s the general process of getting visual signals to the brain?
- Optic nerve > Lateral Geniculate Nucleus (LGN, found within the thalamus) > Visual cortex of the brain
- Each eyeball sends signals from their field of view to both sides of the brain
- Optic nerves cross over at the optic chiasm, which is found before the LGN
What does the thalamus do?
- Doesn’t do any major processing, primarily acts as a relay station for the brain
The left field of view corresponds to…
… The right side of the brain
- The right field of view = left side of the brain
What does topographic organization mean?
- Means that adjacent retinal cells in the retina will also activate adjacent cells in the visual cortex
- Can be thought of as a map of the visual scene
What’s cortical magnification?
- Due to the high density of photoreceptors (primarily cones) found at the fovea, the image at this spot is disproportionately magnified at this spot in the visual cortex
- Cones have great acuity and poor convergence, which contributes to this concept
What are feature detectors?
- Responsible for detecting basic features in the visual scene based on specific patterns of firing in the retina
- Helps maintain the topographic positioning
- There are approximately 10ish types of feature detectors (ex. colour, texture, depth, etc.)
What does the Principle of Neural Representation state?
- Everything we experience is based not on direct contact with stimuli, but on representations (neural code) in the receptors in our brain
- Brain only speaks the language of action potentials
What are complex feature detectors?
- Neurons located in the temporal lobe that increase firing rates when we see certain objects with multiple features (ex. identifying a face)
- A form of hierarchical processing
What does parallel processing signify?
- The feature maps can be processed independently in order to perceive its own separate image (ex. using colour only)
What are the three parts of the brain that make up the visual association cortex?
- Occipital lobe (where visual signals go first)
- Parietal lobe (dorsal stream) = associates action with vision
- Temporal lobe (ventral stream) = associates object perception with vision
What does the Pandemonium model attempt to describe?
- Used to describe letter recognition
- Specific feature detectors can be thought of like a rowdy group of shouting demons
- Most demons both listen and shout, also meaning they receive and send signals
- Doesn’t necessarily encapsulate the complexity of the world around us
What’s the Recogition-by-Components (RBC) model?
- Claims that there are 36 fundamental geons from which we make up all real-world objects
- Geons = 3D volumetric shapes
- All objects have a unique configuration of geons
- Invented by Irving Biedermann (1987)
What’s the Principal of Componential Recovery?
- Apart of the RBC model
- As long as we can perceive the relative size/placement of a few of the geons of an object, we can recognize it
What may some top-down influences include?
- Prior knowledge, expectations, attention, etc.
- This knowledge can sensitize the visual system, making it easier to recognize them
Where was lateral inhibition first demonstrated?
- In horseshoe crabs cause they have a unique eye structure made up of ommatidia, where there’s a lens over each receptor, making it easier to remember
- The lateral plexus is what caused the lateral inhibition
What causes lateral inhibition in humans?
- Inhibition transmitted ‘horizontally’ across the retina
- Done by the horizontal cells and the amacrine cells in humans
Why do we perceive faint dark spots at the white intersections of the Hermann grid when the eyes scan over it?
- It’s because the intersectional ganglion cells experience more lateral inhibition because they are surrounded by other bright spots, so the inhibition transferred from the horizontal and amacrine cells is higher, causing the intersection to appear darker for a brief moment when located within our periphery
- The corridor ganglion cells experience less lateral inhibition due to the dark sides which don’t stimulate the eyes as much
What’s simultaneous contrast?
- Perception of brightness in one area is affected by the presence of an adjacent or surrounding area
- Think Mach bands
Where does the majority of neural processing occur?
- In the brain!
What’s a receptive field?
- The area on the receptor surface that, when stimulated, affects the firing of a given neuron
- Receptor surfaces include skin, tongue, retina, etc.
- One neuron’s receptive fields often overlap those of other neurons
- A neuron’s receptive field can encompass hundreds to thousands of receptors at once
- Convergence is also a big factor. There are 126 million receptors and only 1 million ganglion cells
- For eyes, RECEPTIVE FIELDS ARE FOUND ON THE RETINA!
What does it mean when retinal ganglion cells exhibit center-surround organization?
- The central region of the receptive field affects neuron firing differently than the surrounding region
What does an excitatory-center, inhibitory-surround receptive field signify?
- When receptors in the middle are stimulated, there’s an increase in the firing rate
- When receptors on the edges are stimulated, there’s a decrease in the firing rate
- Sometimes called ‘on-center’ RF
