Chapter 5 Flashcards
How do we see as humans?
We see because light strikes the retina, sending a message to the brain.
What are the connections from the eyes to the brain?
When light activates the bipolar cells at the back of the eye, these bipolar cells send their messages to the ganglion cells. The ganglion cells’ axons unite and travel back to the brain as the optic nerve.
How do connections from the eyes to the brain produce a blind spot in the eye?
The ganglion cell axons join to form an optic nerve which exists through the back of the eye - the point where it leaves is the blind spot. It contains photopigments, chemicals that release energy when struck by light
What are the main properties of cones?
They are abundant in and near the fovea, are more useful in bright light and essential for color vision. It contains photopigments, chemicals that release energy when struck by light
What are the main properties of rods?
They are abundant in the periphery of the retina, respond to faint light but are less useful in daylight because bright light bleaches them
What are the main features of colour vision?
- It is made of electromagnetic radiation within 400nm and 700nm.
- The trichromatic theory (Helmholtz) - The idea that we percieve colour through 3 different kinds of cones sensitive to different wavelengths, with the colour of light determined by comparing the different responses of the cones. There are less blue cones in comparison to the rest.
- The opponent-process theory - we percieve colour in terms of opposites. The brain has a mechanism that perceives color on a continuum from red to green, another from yellow to blue, and another from white to black. After you stare at one color in one location long enough, you fatigue that response and tend to swing to the opposite.
- The retinex theory - the cerebral cortec compares information from various parts of the retina to determine the brightness and color for each area, explaining colour constancy.
Explain the route of visual information from the retina to the cerebral cortex.
- Rods and cones of the retina make synapses with horizontal cells and bipolar cells.
- The horizontal cells make inhibitory contact onto bipolar cells, which in turn make synapses onto amacrine cells and ganglion cells
- The axons of the ganglion cells form the optic nerve, which leaves the retina and travels along the lower surface of the brain until the optic chiasm where half the axons from each eye cross to the opposite side of the brain.
- Most of the optic nerve goes to the lateral geniculate nucleus of the thalamus, others go to the superior colliculus and to the part of the hypothalamus that controls the waking-sleeping shceduale.
What is lateral inhibition in terms of the connections among neurons in the retina?
Lateral inhibition is the retina’s way of sharpening contrasts to emphasize the borders of objects. The receptors in the retina send messages to excite nearby bipolar cells and they also send messages to horizontal cells that slightly inhibit those bipolar cells and the neighbors to their sides. The net result heightens the contrast between an illuminated area and its darker surround.
What are receptive fields?
How does experiences alter development of the visual cortex?
What are the differences between the ventral and dorsal streams of the visual system?
What are the brain mechanisms for perceiving shapes, faces, and movement?
What are horizontal cells?
The laterally interconnecting neurons in the Inner Nuclear (Bipolar) layer of the retina ofmammalian eyes.
