Lesson 3 Flashcards
The Eye
Wavelengths
Is what we are actually looking at when we look at visible light.
- Visible light to the human eye
- Defined as the distance from the peak of one light or sound, to the peak of the next
Cornea
Protects the eye and bends light to provide focus (front of the eye)
Lens
The transparent structure behind the pupil that changes shape to help focus images on the retina (a process known as accommodation)
Retina
Light sensitive inner surface of the eye, containing the photoreceptor rods and cones plus layers of neurons that begin the processing of visual information.
Blind Spot
The point where the optic nerve leaves the eye, creating a blind spot because no receptor cells are located there.
Optic (visual) nerve
The nerve that carries neural impulses from the eye to the brain
Fovea
The central focal point in the retina, around which the eyes cones cluster
Rods
Retinal receptors that detect black, white and gray.
- Necessary for peripheral and dim-light vision.
- Share bipolar cells: sending combined messages.
Cones
Retinal receptor cells that are concentrated near the center of the retina and that function in daylight or in well-lit conditions.
- Detect fine detail and enable you to perceive colour.
- In dim-light they become ineffectual.
- Each cone transmits to a single bipolar cell that relays the cone’s individual message to the visual cortex (via the thalamus).
Near-sighted
Too much curvature (via accommodation) of the lens focuses the image in front of the retina so nearby objects are seen more clearly than distant objects.
Far-sighted
Too little curvature of the lens (via accommodation) focuses the image behind the retina so distant objects are seen more clearly than nearby ones.
Young-Helmholtz trichromatic (3-colour theory)’
The retina contains 3 different colour receptors (cones), each one especially sensitive to 1 of the 3 colours.
When we stimulate combinations of these cones, we see other colours.
Example: there are no cone receptors sensitive to yellow but we can see this colour when mixing red and green light, which stimulates both red-sensitive and green-sensitive cones.
Colourblind
People who are colourblind lack a functioning red or green, or both sensitive cones.
-Can be monochromatic (one-colour) or dichromatic (two-colour)
- Color vision deficiency in which one of the three cone cells is absent or not functioning and color is thereby reduced to two dimensions - means they find it difficult, or cannot, distinguish red and greens.
Opponent-process theory
Suggests that the way humans perceive colors is controlled by three opposing systems.
- Suggests that afterimages come from looking at one color for a long period, which causes those receptor cells to become fatigued.
When they begin sending weaker signals, their opposing cells fire, sending signals that cause the perception of the opposing color.
Afterimages
Defined as sense experiences that occur after a visual stimulus has been removed.
Occipital lobe
Damage to the occipital lobe through stroke or an accident can result in disorders such as:
- Prosopagnosia (Face Blindness)
- Blindsight
Prosopagnosia (Face Blindness)
Damage leads to an interruption of different aspects of the face-recognition process. The person has difficulty or cannot recognise other peoples faces, and even their own.
Blindsight
This is when visual information from the eye is being processed unconsciously, so people with blindsight don’t know that they are visually processing.
You are classified blind if you have no conscious awareness of visual information.
However, blindsight shows us that there is an existence of different visual processing areas in the brain that are responsible for isolated features of vision. Even if the occipital lobe is damaged, there are other area still processing visual information without awareness
Photoreceptors
Special cells in the eye’s retina that are responsible for converting light into signals that are sent to the brain. Photoreceptors give us our color vision and night vision. There are two types of photoreceptor cells: rods and cones.
Ganglion Cells
Projection neurons of the vertebrate retina that transmit information from other retinal neurons to the brain .
Accommodation
The ability of the eye to focus on near and far objects . While focusing on the distant object and moving to a near object, the focus is not lost. As the lens in the eye flattens out and becomes thin, the eye uses less reflective power and can focus on a distant object.
