W1 Flashcards
(21 cards)
What is the neural basis of vision and action?
The neural basis of vision and action involves a complex interplay between visual, motor, and cognitive systems, with unconscious brain processes significantly influencing our actions.
What are planning choices?
Studies have shown our brain considers:
Duration
Path
Velocity
Joint angles
Muscle activity
Neural firing pattern
What are motor invariants?
Sequenced stereotyped trajectories for eye and arm movements including path and velocity
Why do motor invariants exist? JTE
Minimum jerk hypothesis: We optimise the smoothness of our movement
Minimum torque-change model: We try to minimise forces around our joints
Minimum endpoint variance: We minimise variance at end of our movement
Model limitations → Similar predictions, making it difficult to determine the most accurate theory.
What is the neuromuscular junction? (NMJ)
The bridge between the brain and muscles.
The NMJ is a crucial point where motor neurons connect with muscle fibres. When a motor neuron fires, it creates a strong response at the neuromuscular junction, causing filaments to contract. This is the basis of all our movements
How is the neuromuscular junction adapted? (NMJ)
You’ll find a highly convoluted surface (twists and turns) in the post-synaptic cell (muscle fibre).
This intricate folding significantly increases the surface area.
A larger surface area is needed for motor neurons and muscle fibres to connect + translate to more receptors activating → stronger connection.
A single action potential originating from the motor neuron can effectively trigger a muscle contraction.
How do the eyes and the brain CONNECT?
The brain exclusively receives information about the external world through the retina, the light-sensitive layer at the back of the eyeball.
Light-sensitive cells on the retina detect specific frequencies of light.
These cells process the information before transmitting it to a smaller number of ganglion cells.
The output from the ganglion cells forms the optic nerve, which carries the visual information to the brain.
How do we exploit forced perspective?
A technique employing opticial iollusions to make an object appear closer/further or larger/smaller than what it.
What is pareidolia?
Pareidolia, the brain’s tendency to perceive faces in random stimuli (like “Jesus” in toast), involves activation of the fusiform gyrus, a brain region crucial for face recognition.
Why don’t we see things as they are?
Resolution problem: If the eyes recorded everything like video cameras, the sheer volume of data would be overwhelming.
**The energy problem: **Constant retinal cell activity would require immense energy, leading to a significant increase in blood vessels and a large blind spot. (The brain, despite sophisticated energy-saving mechanisms, consumes 20% of the body’s power, equivalent to a low-power lightbulb.)
What’s the solution to this?
The Compression Mechanism!
We only transmit important information (not things humans don’t need to react to.)
Changes are prioritised over stuff that stays the same
We only detect new objects that move
Consequences of this:
Highly responsive to immediate events and fine details in black and white, but struggles to perceive gradual shifts or subtle color variations.
Well-suited for tasks requiring rapid comparisons within a fixed timeframe, but less effective for assessing long-term trends or making absolute determinations.
What are encoding changes over space?
When the brain is overstimulated, it responds by inhibiting active signals to maintain balance. Thus the brain processes visual information efficiently by adapting to repeated patterns across space.
G-cells detect green at different locations.
Lateral inhibition occurs when spatial inhibitor cells suppress neighboring active cells.
Each G-cell has a corresponding spatial inhibitor cell that regulates its activity.
Adaptation is fast—it activates and fades quickly.
The brain compresses signals that remain constant across space to enhance efficiency.
So how does context affect perception?
Color Perception & Opponent Process Theory
The visual system processes colors using opponent cells (e.g., red-green, blue-yellow).
Seeing green activates green-sensitive cells while inhibiting red-sensitive cells.
If both red and green cells activate, the brain perceives an orangey color.
Cell Activation & Contrast Effects
Changing focus or stimuli activates different cells.
Strong activation of red-sensitive cells leads to spatial inhibition, suppressing surrounding opposing-color cells to enhance contrast.
Adaptation & Colour Aftereffects
Prolonged colour exposure overstimulates and fatigues corresponding cells.
Sensory adaptation weakens their response, leading the brain to compensate by activating opposite colour cells (e.g., afterimages).
This process involves spatial inhibition (enhancing contrast) and computational inhibition (adjusting perception balance).
Contrast Enhancement by the Brain
The brain prioritises contrast over absolute colour perception.
It suppresses prolonged activation and highlights differences, creating afterimages or altered colour perception when stimuli change.
What is the Craik O’brien-Cornsweet illusion?
This is a visual trick where a subtle gradient at the edge of two areas makes one appear lighter and the other darker, even though they’re the same shade.
It shows how our brains interpret edges and contrast to perceive brightness.
What is lateral inhibition?
Lateral inhibition disables the spreading of action potentials from excited cells to neighbouring cells. This enhances contrast and sharpens sensory information.
It’s like your brain is turning up the volume on the loudest signals and quieting the rest, so you can perceive details more clearly.
This happens in your eyes to help you see edges and in your skin to help you feel textures.
Illusions:
Lilac Chaser: Moving color/disappearing discs due to afterimages and motion perception.
Craik–Cornsweet–O’Brien: Edges trick us into seeing different shades of the same color.
Troxler’s Effect: Peripheral stationary objects fade when you stare at a point.
Simultaneous Contrast: Surrounding colors change how we see a central color.
What is path vs velocity
Path: sequence of the position of the hand in space
Velocity: time sequence of along a path
