Lecture 2 Flashcards
(30 cards)
What is perception?
It is the active organising, identifying and interpreting of sensory information to comprehend the environment and to guide actions. Interpretations being based on knowledge/experience.
What is the difference between sensation and perception?
Sensation is the biological, passive process from triggering sensors via raw stimuli. Perception is not an accurate measurement of the outside world but rather an intepretation of that sensory input.
Where does perception happen?
From sensory organs like the five senses and others like time, facial and emotional perception
Why is visual perception important?
Half of the neocortex is dedicated to visual processing and we know most about the visual system as it is full of illustrative examples. Vision is also are most trusted sense, it even changes how we percieve sounds and other senses
What is the visual pathway?
Light enters through the lens to the retina; going through ganglion cells to bipolar cells and horizontal cells and then photoreceptors. The light is then transduced into electrical potentials that are then communicated to the bipolar cells and then ganglion cells where their axons connect to the neurons in the optic nerve.
What is the fovea?
It is the center of your visual field dominated by photo receptors with no ganglion or bipolar cells covering them.
What are the types of 100 million photoreceptors?
We have cones that are densely packed in the fovea and responsible for daylight vision in fine detail and colour vision. Rods are good for night vision and are reponsible for translating the periphery
What is the optic disk?
The point were all the axons of the ganglion cells exit the eye; where we have a blindspot. Brain fills in the blind spot by making an “informed guess” based on surroundings, showing how perception is not a true replication of the world as we know it.
What is the hyper early form of perception in the retina?
Even in the retina already, photoreceptors interact to emphasize meaningful aspects of the input. This is through methods like lateral inhibition,
What is lateral inhibition?
So when a stimulus have a dark and light side, the light side fires more action potentials than the dark. Horizontal cells inhibit their neighbours so when it has fires a lot of action potentials, it inihibits a lot from their low firing neighbour creating contrast and edges.
How does visual processing continue to the primary visual cortex from the eye?
Light from the left reaches the right side of both eyes and vice versa. This leads to the optic nerves having an optic chiasm (meeting point) which switches the left fields to the left hemisphere and the right fields to the right hemisphere. This then moves to the lateral geniculate nucleus (image enhancement) and then to the visual cortex with axons going to different parts. visual areas are organised as maps of space so where they are on the retina is approximate to where they are on V1 (fovea takes up 40% though)
What does the superior colliculus do?
It moves the eye through reflexive, rapid motions when something spikes interest in ones visual field
What are some features of the visual cortex?
It is hierarchical (V1 > V2 > V3 etc.) and it is also has distributed parallel processing in functionally specialised areas
How does coding in the sensory cortex work?
Neurons detect visual features such as edges, lines, orientations etc. However, different neurons detect different features and are activated differently. By weighing inputs, they are turned to that feature and output firing rate informs higher-level neurons (like a horizontal line + vertical line = corner). Neurons with similar functions communicate easily as they are close together which leads to the specialisation of brain areas.
What is the region of visual field that a neuron responds to?
Receptive Field
How does information change in the visual pathway?
The further it goes along the visual pathway, the more complex the tuning becomes and the larger receptive fields become
How did we discover information about visual pathways?
Research from Hubel and Wiesel where, with a small electrode, they were able to measure the activation of certain cells with certain stimuli and find a relationship between the two
What are the famous dissociations (specialisations) of neural pathways?
- “what” pathway (ventral stream) which is tuned for objects and faces and feeds into memory areas (medial temporal lobe)
- “Where/how” pathway (dorsal stream) which is tuned for location, motion and direction which informs the motor cortex, eye movement system and attention (essentially vision for action)
Are pathways isolated?
No, visual pathways are not isolated and everything in the brain “talks” to each other as object knowledge form the ventral stream can inform actions and “motion” from the dorsal stream can be a part of episodic memories in the medial temporal lobe. A pathway is more about the type of computations done by neurons than strictly seperated information.
What are the “solutions” to the binding problem?
- Spatial location - although they form in different areas of the brain, they assemble to the same area in space > we also perceive two objects in the same space via attention
- Synchronized, rhythmic firing - leads to the combination of neural activation that leads to one sensory experience
What is a major issue in the binding problem?
How do we perceptually group objects. After detecting a bunch of a feature, how do we know it belongs to one feature? Essentially how do we understand grouping and object segmentation. Gestalt psychology aims to answer this.
What are Gestalt laws?
They are rules for grouping that suggest that the mind organises sensory input as wholes and not sums of parts
What are some examples of Gestalt systematic grouping rules?
- Proximity - perceiving dotes as being grouped together depending on the closeness of the objects in space
- Similarity - grouping based on similarity
- Good continuation - grouping based objects aligning on a smooth path
- Closure - bias to perceiving closed figures when they aren’t closed
- Simplicity - bias to elements being grouped together in the easiest way to understand/interpret
- Common fate - grouping based on objects moving in the same direction
What are the criticisms of gestalt psychology?
They are useful descriptions of perceptual principles but they don’t explain the why and they aren’t really laws, just regularities. Gestalt perception is also based on experience rather than some innate quality.
