👁️
Chapter 4: Sensation and
Perception
Topic 1 - The Visual System
Terminology:
Sensation: the stimulation of the senses, through the sensory receptors of our sensory
organs.
Perception: is the selection, organization, and interpretation of the incoming sensation.
Transduction: a subprocess that occurs during sensation.
Threshold: a dividing point between energy levels that do and do not have an effect.
Absolute threshold: the minimum amount of stimulation an organism can detect.
Just noticeable difference: the smallest difference in the amount of stimulation a
specific sense can detect.
Sensory adaptation: a gradual decline in the sensitivity to prolonged stimulation; similar
to habituation.
1.1) The stimulus: Light
To see there must be light.
Light is a form of electromagnetic radiation that travels as a wave. Light waves vary in
amplitude(height) and in wavelength(the distance between peaks).
Amplitude: affects mainly the perception of brightness
Wavelength: affects mainly the perception of color
Light can also vary in its purity (how varied the mix is). Purity influences the perception of
the saturation or richness of colors.
Saturation: refers to the relative amount of whiteness in a color; as whiteness declines
saturation increases.
Chapter 4: Sensation and Perception 1
, The visible spectrum is only a small portion of what humans can see
humans can’t see on the ultraviolet or infrared spectrum
incoming visual input (what you see) is converted into neural impulses that re-sent to the
brain
1.2) The eye: Living optical instrument
The role of the lens and the pupil in the functioning of the eye:
1. Light (stimulus energy) enters the eye through the transparent window at the front -
cornea
2. And moves through the pupil (black dot-hole) - the lens behind the cornea focuses the
light rays forming the retina.
3. In doing so an upside-down image of objects falls onto the retina,
4. The lens then adjusts/focuses the image
Lens: a transparent eye structure that focuses the light rays falling on the retina.
Lens is made up of a relatively soft tissue, capable of adjustments that facilitate a process
called accommodation.
Accommodation: occurs when the curvature of the lens changes to alter visual focus.
When you focus on a close object, the lens of your eye gets rounder (fatter) to give a clear
image.
When you focus on a far object, the lens of your eye flattens to give a better image.
Pupil: regulates the amount of light reaching the retina
constricts to allow less light and therefore gives a sharper image
Iris: surrounds it and is a colored ring of muscle
Common visual problems (caused by focusing problems or defects on the lens:
Nearsightedness: can see clearly objects that are close, but blurry when objects are far. -
focus of light falls short on the retina.
Farsightedness: sees objects that are far very well, while close objects are blurry. - focus
of light falls short behind the retina.
Cataract: when your lens is clouded
Chapter 4: Sensation and Perception 2
, 1.3) The retina:
Retina: neural tissue lining the inside back surface of the eye
It is a complex layer of specialized cells arranged in layers.
Functions:
Absorbs light
Processes images
Sends visual information (images) to the brain
The axons that run from the retina to the brain meet at a single spot where they exit the eye.
At that point, all the fibers drive through a hole in the retina called the optic disk.
Optic disk: a hole in the retina, where you cannot see the part of an image that falls on it —>
this is known as the blind spot
Visual receptors of the retina: Rods and cones
Cones: specialized visual receptors that play a key role in daylight and color vision
Cones provide better visual acuity - sharpness and precise detail.
Cones are concentrated in the center of the retina and quickly decrease in density towards
its sides.
- This area is called the
fovea: a tiny spot in the center of the retina that contains only cones.
Rods: specialized visual receptors that play a key role in night vision and peripheral vision.
Are found on the outer areas of the retina.
Elongated
Play a role in peripheral vision
Dark adaptation:
The process in which our eyes become more sensitive to light in low illumination. —>
Example: when you enter a dark room your eyes will focus on whatever light is available
Light adaptation:
The process in which our eyes become less sensitive to light in high illumination. —>
Example: when you live in the house and step outside on a bright, sunny day.
Information processing in the retina
Chapter 4: Sensation and Perception 3
Chapter 4: Sensation and
Perception
Topic 1 - The Visual System
Terminology:
Sensation: the stimulation of the senses, through the sensory receptors of our sensory
organs.
Perception: is the selection, organization, and interpretation of the incoming sensation.
Transduction: a subprocess that occurs during sensation.
Threshold: a dividing point between energy levels that do and do not have an effect.
Absolute threshold: the minimum amount of stimulation an organism can detect.
Just noticeable difference: the smallest difference in the amount of stimulation a
specific sense can detect.
Sensory adaptation: a gradual decline in the sensitivity to prolonged stimulation; similar
to habituation.
1.1) The stimulus: Light
To see there must be light.
Light is a form of electromagnetic radiation that travels as a wave. Light waves vary in
amplitude(height) and in wavelength(the distance between peaks).
Amplitude: affects mainly the perception of brightness
Wavelength: affects mainly the perception of color
Light can also vary in its purity (how varied the mix is). Purity influences the perception of
the saturation or richness of colors.
Saturation: refers to the relative amount of whiteness in a color; as whiteness declines
saturation increases.
Chapter 4: Sensation and Perception 1
, The visible spectrum is only a small portion of what humans can see
humans can’t see on the ultraviolet or infrared spectrum
incoming visual input (what you see) is converted into neural impulses that re-sent to the
brain
1.2) The eye: Living optical instrument
The role of the lens and the pupil in the functioning of the eye:
1. Light (stimulus energy) enters the eye through the transparent window at the front -
cornea
2. And moves through the pupil (black dot-hole) - the lens behind the cornea focuses the
light rays forming the retina.
3. In doing so an upside-down image of objects falls onto the retina,
4. The lens then adjusts/focuses the image
Lens: a transparent eye structure that focuses the light rays falling on the retina.
Lens is made up of a relatively soft tissue, capable of adjustments that facilitate a process
called accommodation.
Accommodation: occurs when the curvature of the lens changes to alter visual focus.
When you focus on a close object, the lens of your eye gets rounder (fatter) to give a clear
image.
When you focus on a far object, the lens of your eye flattens to give a better image.
Pupil: regulates the amount of light reaching the retina
constricts to allow less light and therefore gives a sharper image
Iris: surrounds it and is a colored ring of muscle
Common visual problems (caused by focusing problems or defects on the lens:
Nearsightedness: can see clearly objects that are close, but blurry when objects are far. -
focus of light falls short on the retina.
Farsightedness: sees objects that are far very well, while close objects are blurry. - focus
of light falls short behind the retina.
Cataract: when your lens is clouded
Chapter 4: Sensation and Perception 2
, 1.3) The retina:
Retina: neural tissue lining the inside back surface of the eye
It is a complex layer of specialized cells arranged in layers.
Functions:
Absorbs light
Processes images
Sends visual information (images) to the brain
The axons that run from the retina to the brain meet at a single spot where they exit the eye.
At that point, all the fibers drive through a hole in the retina called the optic disk.
Optic disk: a hole in the retina, where you cannot see the part of an image that falls on it —>
this is known as the blind spot
Visual receptors of the retina: Rods and cones
Cones: specialized visual receptors that play a key role in daylight and color vision
Cones provide better visual acuity - sharpness and precise detail.
Cones are concentrated in the center of the retina and quickly decrease in density towards
its sides.
- This area is called the
fovea: a tiny spot in the center of the retina that contains only cones.
Rods: specialized visual receptors that play a key role in night vision and peripheral vision.
Are found on the outer areas of the retina.
Elongated
Play a role in peripheral vision
Dark adaptation:
The process in which our eyes become more sensitive to light in low illumination. —>
Example: when you enter a dark room your eyes will focus on whatever light is available
Light adaptation:
The process in which our eyes become less sensitive to light in high illumination. —>
Example: when you live in the house and step outside on a bright, sunny day.
Information processing in the retina
Chapter 4: Sensation and Perception 3
