Summary
Sensation and Perception
UU
Inhoudsopgave
Chapter 2 The first steps in vision: From light to neural signals........................2
Chapter 3 Spatial vision: From spots to stripes................................................6
Chapter 4 Perceiving and recognizing objects..................................................9
Chapter 5 Perception of color........................................................................12
Chapter 6 Space perception and binocular vision...........................................15
Chapter 7 Attention and Scene perception....................................................16
,Chapter 2 The first steps in vision: From light to neural signals
Light physics
Light is a form of electromagnetic radiation = energy produced by vibrations of electrically
charged material.
- Waves
- Photons
Light is made up of waves when it moves around the world and being made up of photons
when it is absorbed.
Visible light waves have wavelengths between 400 and 700 nanometers. As wavelengths vary
in the visual spectrum, the hue we observe changes.
When light strikes a light-colored surface, most of the light is reflected. This is what gives the
surface its ‘light’ appearance.
Most of the light striking a dark surface is absorbed
When light is neither reflected nor absorbed, it is transmitted through the surface. As light is
transmitted (through a window), some of the waves will be refracted (=alter course).
Physiological mechanism: eyes that capture light
An eye can form an image of the outside world, enabling animals to use light to recognize
objects.
Cornea = the transparent ‘window’ into the eyeball, it is transparent, most light photons are
transmitted through it. It contains no blood vessels and is made of a highly ordered
arrangement of fibers. It does have a rich supply of transparent nerve endings
Aqueous humour = the watery fluid in the anterior chamber of the eye. The fluid is derived
from blood and supplies oxygen and nutrients to, and removes waste from, both the cornea
and the lens.
Lens = the structure inside the eye that enables the changing of focus. Also, completely
transparent and without blood supply.
Pupil = the dark circular opening at the center or the iris in the eye, where light enters.
Iris = the colored part of the eye, consisting of a muscular diaphragm surrounding the pupil
and regulating the light entering the eye by expanding and contracting the pupil. This happens
via the pupillary light reflex: the iris automatically expands or contracts to allow more or less
light.
Vitreous humour = the transparent fluid that fills the vitreous chamber in the posterior part of
the eye. This chamber comprises 80% of the internal volume of the eye.
Retina = a light-sensitive membrane in the back of the eye that contains photoreceptors and
other cell types that transduce light into electrochemical signals (= transduction) and transmit
them to the brain through the optic nerve. Only some of the light will actually reach the retina.
Focusing light onto the retina
Accommodation = the process of altering the refractive power by changing the shape of the
lens. It changes the focus.
Accomplished through contraction of the ciliary muscle. The lens is attached to this muscle
through tiny fibers called the zonules of Zinn.
When the muscle is relaxed, the zonules are stretched and the lens is flat. In this state, the eye
will be focused on very distant objects.
, When the muscle contracts, it reduces the tension on the zonules and enables the lens to
bulge. The fatter the lens is, the closer you can focus.
The ability to accommodate declines with age. presbyopia = ‘old sight’ the age related
loss of accommodation, which makes it difficult to focus on near objects. Because the lens
becomes harder and the surrounding capsule loses elasticity.
Emmetropia = the condition in which there is no refractive error, because the refractive
power is perfectly matched to the length of the eyeball
Refractive errors occur when the eyeball is too long or too short relative to the power of the
4 components.
- Myopia = nearsightedness, they cannot see distant objects clearly. The eyeball is too
long. Can be corrected with negative (minus) lenses.
- Hyperopia = farsightedness, the eyeball is too short and the image will be focused
behind the retina. If it is not too severe, it can be compensated with accommodation. If
this fails, it can be corrected with positive (plus) lenses
Fundus = the back layer of the retina
Optic disc = the point where the arteries and veins that feed the retina enter the eye and where
axons of the ganglion cells leave the eye via the optic nerve. This portion contains no
photoreceptors and is therefore also called the ‘blind spot’.
Fovea = a small pit located near the center of the macula and containing the highest
concentration of cones and no rods. It is the portion of the retina that produces the highest
visual acuity and serves as the point of fixation.
Two types of photoreceptors:
- Rods = specialized for night vision
- Cones = specialized for daylight vision, fine visual acuity and color vision
Dark and light adaption
- Pupil size: only accounts for a small part of the system to adapt to light and dark
conditions
- Photopigment regeneration
Most important: neural circuitry.
A ganglion cell is most sensitive to differences in the intensity of the light in the center and in
the surround of its receptive field (= the region of the retina in which visual stimuli influence
a neuron’s firing rate).
Retinal information processing
When photoreceptors capture light, they produce chemical changes that start a cascade of
neural events ending in a visual sensation.
Outer segment = contains photopigment molecules
Inner segment = between the outer segment and the nucleus
Synaptic terminal = the location where axons terminate at the synapse for transmission of
information by the release of a chemical transmitter.
Visual pigments are made in the inner segment and stored in the outer segment. They consist
of an opsin (protein), which determines which wavelengths the pigment molecule absorbs,
Sensation and Perception
UU
Inhoudsopgave
Chapter 2 The first steps in vision: From light to neural signals........................2
Chapter 3 Spatial vision: From spots to stripes................................................6
Chapter 4 Perceiving and recognizing objects..................................................9
Chapter 5 Perception of color........................................................................12
Chapter 6 Space perception and binocular vision...........................................15
Chapter 7 Attention and Scene perception....................................................16
,Chapter 2 The first steps in vision: From light to neural signals
Light physics
Light is a form of electromagnetic radiation = energy produced by vibrations of electrically
charged material.
- Waves
- Photons
Light is made up of waves when it moves around the world and being made up of photons
when it is absorbed.
Visible light waves have wavelengths between 400 and 700 nanometers. As wavelengths vary
in the visual spectrum, the hue we observe changes.
When light strikes a light-colored surface, most of the light is reflected. This is what gives the
surface its ‘light’ appearance.
Most of the light striking a dark surface is absorbed
When light is neither reflected nor absorbed, it is transmitted through the surface. As light is
transmitted (through a window), some of the waves will be refracted (=alter course).
Physiological mechanism: eyes that capture light
An eye can form an image of the outside world, enabling animals to use light to recognize
objects.
Cornea = the transparent ‘window’ into the eyeball, it is transparent, most light photons are
transmitted through it. It contains no blood vessels and is made of a highly ordered
arrangement of fibers. It does have a rich supply of transparent nerve endings
Aqueous humour = the watery fluid in the anterior chamber of the eye. The fluid is derived
from blood and supplies oxygen and nutrients to, and removes waste from, both the cornea
and the lens.
Lens = the structure inside the eye that enables the changing of focus. Also, completely
transparent and without blood supply.
Pupil = the dark circular opening at the center or the iris in the eye, where light enters.
Iris = the colored part of the eye, consisting of a muscular diaphragm surrounding the pupil
and regulating the light entering the eye by expanding and contracting the pupil. This happens
via the pupillary light reflex: the iris automatically expands or contracts to allow more or less
light.
Vitreous humour = the transparent fluid that fills the vitreous chamber in the posterior part of
the eye. This chamber comprises 80% of the internal volume of the eye.
Retina = a light-sensitive membrane in the back of the eye that contains photoreceptors and
other cell types that transduce light into electrochemical signals (= transduction) and transmit
them to the brain through the optic nerve. Only some of the light will actually reach the retina.
Focusing light onto the retina
Accommodation = the process of altering the refractive power by changing the shape of the
lens. It changes the focus.
Accomplished through contraction of the ciliary muscle. The lens is attached to this muscle
through tiny fibers called the zonules of Zinn.
When the muscle is relaxed, the zonules are stretched and the lens is flat. In this state, the eye
will be focused on very distant objects.
, When the muscle contracts, it reduces the tension on the zonules and enables the lens to
bulge. The fatter the lens is, the closer you can focus.
The ability to accommodate declines with age. presbyopia = ‘old sight’ the age related
loss of accommodation, which makes it difficult to focus on near objects. Because the lens
becomes harder and the surrounding capsule loses elasticity.
Emmetropia = the condition in which there is no refractive error, because the refractive
power is perfectly matched to the length of the eyeball
Refractive errors occur when the eyeball is too long or too short relative to the power of the
4 components.
- Myopia = nearsightedness, they cannot see distant objects clearly. The eyeball is too
long. Can be corrected with negative (minus) lenses.
- Hyperopia = farsightedness, the eyeball is too short and the image will be focused
behind the retina. If it is not too severe, it can be compensated with accommodation. If
this fails, it can be corrected with positive (plus) lenses
Fundus = the back layer of the retina
Optic disc = the point where the arteries and veins that feed the retina enter the eye and where
axons of the ganglion cells leave the eye via the optic nerve. This portion contains no
photoreceptors and is therefore also called the ‘blind spot’.
Fovea = a small pit located near the center of the macula and containing the highest
concentration of cones and no rods. It is the portion of the retina that produces the highest
visual acuity and serves as the point of fixation.
Two types of photoreceptors:
- Rods = specialized for night vision
- Cones = specialized for daylight vision, fine visual acuity and color vision
Dark and light adaption
- Pupil size: only accounts for a small part of the system to adapt to light and dark
conditions
- Photopigment regeneration
Most important: neural circuitry.
A ganglion cell is most sensitive to differences in the intensity of the light in the center and in
the surround of its receptive field (= the region of the retina in which visual stimuli influence
a neuron’s firing rate).
Retinal information processing
When photoreceptors capture light, they produce chemical changes that start a cascade of
neural events ending in a visual sensation.
Outer segment = contains photopigment molecules
Inner segment = between the outer segment and the nucleus
Synaptic terminal = the location where axons terminate at the synapse for transmission of
information by the release of a chemical transmitter.
Visual pigments are made in the inner segment and stored in the outer segment. They consist
of an opsin (protein), which determines which wavelengths the pigment molecule absorbs,
