PSY 250 Lecture Notes - Lecture 40: Temporal Lobe, Fusiform Face Area, Lightdark
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Chapter 10: Vision and Visual Perception Book Notes
- Introduction Information
- Vision enables us to read and to absorb large amounts of complex information
- Vision helps us navigate in the world, build structures, and avoid danger
- Color helps distinguish objects from their background, and enriches our lives with natural
beauty and works of art
- Vision has received more research attention than the other senses combined
- We understand a great deal about how the brain processes visual information
- Studies of vision are providing a valuable model for understanding complex neural
processing in general
- Light and the Visual Apparatus
- Vision is an impressive capability
- 126 million light receptors in the human eye and a complex network of cells connecting
them to each other and to the optic nerve
- Optic nerve itself boasts a million neurons, compared with 30,00 in auditory nerve
- Optic nerve transmits information to the brain at an estimated 100 million bits/second
- The Visible Spectrum
- To understand we need to start describing the adequate stimulus
- Visible light is a part of the electromagnetic spectrum
- Electromagnetic spectrum includes a variety of energy forms, ranging from
gamma rays at one extreme of frequency to the radiations of alternating current
circuits at the other
- Visible part of the spectrum accounts for only 1/70 of the range
- Most energies in spectrum aren’t useful for producing images
- Humans can see infrared images only with the aid of specialized equipment, and
this capability is very useful to the military and the police for detecting people and
heat-producing vehicles and armament at night
- Electromagnetic energy within our detectable range produces well-defined
images because it is reflected from objects with minimal distortion
- Our sensory equipment is adapted for detecting the energy that is most useful to
us, just as the night-hunting sidewinder rattlesnake is equipped to detect the
infrared radiation emitted by its prey and a bat’s ears are specialized for the high-
frequency sound waves it bounces off small insects
- List is a form of oscillating energy and travels in waves just as sounds do
- Unit of measurement is a nanometer (nm)
- Visible light ranges from about 400 -800 nm
- The Eye and its Receptors
- Eye is a spherically shaped structure with a clear liquid
- Outer covering (sclera) is opaque except for the cornea, which is transparent
- Behind cornea is lens
- Lens is a flexible tissue and the muscles attached to it can stretch it out flatter to
focus the image of a distant object on the retina, or they can relax to focus on the
image
- Iris gives our eyes color, is a circular muscle whose opening from the pupil, and it
controls the amount of light entering the eye by contracting reflexively in bright
light and relaxing in dim light
- Retina: the light-sensitive structure at the rear of the eye, is made up of two main
types of light sensitive receptor cells, called rods and cones, and the neural cells
that are connected to them
- Receptors (photoreceptors): at the very back of the eye
- Light must pass through the neural cells to reach the photoreceptors, but this
presents little problem because the neural cells are transparent
- Bipolar cells are connected to ganglion cells which form the optic nerve
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- Photopigments: light-sensitive chemicals
- Light passing through the photopigment causes some of the molecules to break
down into 2 components, and the ensuing chemical reaction ultimately results in
a neural response
- 2 components recombine to maintain supply of photopigment
- Rods and cones are named for their shapes
- Human eye contains about 120 million rods and about 6 million cones
- Rhodopsin: rod photopigment
- More sensitive to light
- Rods function better in dim light than cones do
- You rely on your rods for vision in dim light
- Rods barely function in bright light
- The delay in adjusting to a darkened movie theater is due to the time it
takes the rhodopsin to resynthesize
- Rods differentiate only among different levels of light and dark (why we
can’t recognize colors in dim light
- Iodopsin: cone photopigment
- Requires a high level of light intensity to operate
- Cones are nonfunctional in dim light, but function well in daylight
- Three varieties of iodopsin
- Located in different cones
- Respond differentially to different wavelengths of light
- Cones can distinguish among different wavelengths
ROD SYSTEM
CONE SYSTEM
FUNCTION
Functions best in dim light,
poorly or not at all in bright
light.
Detail vision is poor.
Does not distinguish colors.
Functions best in bright light,
poorly or not at all in dim light.
Detail vision is good.
Distinguishes among colors.
LOCATION
Mostly in periphery of retina.
Mostly in fovea and
surrounding area.
RECEPTIVE FIELD
Large, due to convergence on
ganglion cells; contributes to
light sensitivity.
Small, with one or a few
cones converging on a single
ganglion cell; contributes to
detail vision.
- Pathways to the Brain
- Axons of ganglion cells join together and pass out of each eye to form two optic
nerves
- There are no receptors where the nerve exits the eye (blind spot)
- Visual Field: the part of the environment being registered on the retina
- Retinal Disparity: a discrepancy in the location of an object’s image on the two
retinas
- Color Vision
- There is a correspondence between color and wavelength
- Color is a property of the light reflected from an object and of the object itself
- Wavelength doesn’t always predict color
- The term color refers to the observer’s experience rather than a characteristic of the
object
- Example: it is technically incorrect to say that the light is red or that a book is
blue, because red and blue are experiences that are imposed by the brain
- Trichromatic Theory
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Document Summary
Chapter 10: vision and visual perception book notes. Vision enables us to read and to absorb large amounts of complex information. Vision helps us navigate in the world, build structures, and avoid danger. Color helps distinguish objects from their background, and enriches our lives with natural beauty and works of art. Vision has received more research attention than the other senses combined. We understand a great deal about how the brain processes visual information. Studies of vision are providing a valuable model for understanding complex neural processing in general. 126 million light receptors in the human eye and a complex network of cells connecting them to each other and to the optic nerve. Optic nerve itself boasts a million neurons, compared with 30,00 in auditory nerve. Optic nerve transmits information to the brain at an estimated 100 million bits/second. To understand we need to start describing the adequate stimulus. Visible light is a part of the electromagnetic spectrum.
