This document summarizes Chapter 4 of "Psychology: Themes and Variations." It covers visual perception, gustatory perception, touch, hearing, and smell. It also provides information on the structure of the eye and ear, as well as the different theories of visual perception and the auditory system.
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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
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