6.1 Visual Coding Flashcards
When you see grass as green, the green is not a ____ of grass. Green is the experience that results when the light bouncing off grass reacts with the neurons in your brain. Greenness is in us.
property
You ____ an object when it emits or reflects energy that stimulates receptors that transmit information to your brain.
perceive
Your brain stores a representation of a triangle in terms of altered activity in many neurons, and if you examine those neurons, you will see nothing that looks like a triangle. Your brain ____ information in terms of which neurons respond, the amount of response, and the timing of the responses.
codes
One aspect of coding is which neurons are active. Impulses in certain neurons indicate light, where is impulses in others indicate sound. Johannes Muller described this insight is the law of ____ ____ ____.
specific nerve energies
Müller held that whatever excites a particular nerve establishes a special kind of energy unique to that nerve. In modern terms, the brain somehow ____ the action potentials from the auditory nerve as sounds, those from olfactory nerve as odours, and so forth.
interprets
Another aspect of coding is the amount of ____ – that is, how many action potentials a neuron sends per unit of time.
response
Much of sensory coding depends on the ____ of firing. For example, when pain axons fire many action potentials per second, you feel intense pain. Fewer per second would produce less pain.
frequency
Light enters the eye through an opening in the centre of the iris called the ____.
pupil
Light is focused by the ____ (adjustable) and the ____ (not adjustable) and projected onto the ____, the rear surface of the eye, which is lined with visual receptors.
lens : cornea : retina
Light from the ____ side of the world strikes the ____ half of the retina, and vice versa. Light from above strikes the bottom half of the retina, and light from below strikes the top half.
left : right
In vertebrate retina messages go from receptors at the back of the eye to ____ cells, located closer to the centre of the eye. The bipolar cells send their messages to ____ cells, located still closer to the centre of the eye. The ganglion cells axons join together and travel back to the brain.
bipolar : ganglion
Various types of ____ ____ refine the input to ganglion cells, enabling then to respond specifically to shapes, movements, or other visual features.
amacrine cells
Additional cells called ____ cells get information from bipolar cells and send it to other bipolar, amacrine, and ganglion cells.
amacrine
The ganglion cell axons form the ____ ____, which exits through the back of the eye. The point at which leaves (which is also where the blood vessels enter and leave) is the ____ ____ because it has no receptors.
optic nerve : blind spot
In everyday life, and you never notice your blindspot, for two reasons. First, your brain fills in the ___. Second, anything in the blindspot of one eye is ____ to the other eye.
gap : visible
The ____ is a tiny area specialised for acute, detailed vision.
fovea
Because blood vessels and ganglion cells are almost absent near the fovea, it has nearly ____ vision. The tight packing of receptors also aides perception of detail.
unimpeded
More important for perceiving detail, each receptor in the fovea connects to a ____ bipolar cell, which in turn connects to ____ ganglion cell, which has an axon to the brain.
single
The ganglion cells in the fovea of humans and other primates are called ____ ____ ____ because each is small and responds to just a single cone.
midget ganglion cells
Because the midget ganglion cells provide 70% of the input to the brain, our vision is ____ by what we see in the fovea.
dominated
Towards the ____ of the retina, more and more receptors converge on to bipolar and ganglion cells. As a result, the brain cannot detect the exact location or shape of a peripheral light source.
periphery
In short, foveal vision has a better ____ (sensitivity to detail), and peripheral vision has better sensitivity to dim light.
acuity
The vertebrate retina contains two types of receptors: ____ and ____.
rods and cones
The ____, which are abundant in the periphery of the human retina, respond to faint light but are not useful in daylight because bright light bleaches them.
rods
____, which are abundant in and near the fovea, are less active in dim light, more useful in bright light, and essential for colour vision.
Cones
Because of the ____ of rods and cones, you have good colour vision in the fovea but not in the periphery.
distribution
Although rods outnumber cones by about 20 to 1 in the human retina, cones provide about ____ of the brains input.
90%
In the ____, each cone has its own line to brain. In the ____ (mostly rods), each receptor shares a line with tens or hundreds of others.
fovea : periphery
Overall, 120 ____ rods and 6 ____ cones converge into 1 ____ axons in the optic nerve.
million
Both rods and cones contain ____, chemicals that release energy when struck by light.
photopigments
