Chapter Four
Sensation & Perception
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Sensation
The stimulation of sensory
receptors and the transmission of sensory information to the central nervous
system.
A biological process.
How many senses do you have?
Perception
The process by which sensations
are organized into an inner representation of the world.
A psychological process.
making sense of your
sensations
Psychophysics (see p.143)
The study of the relationships
between physical stimuli (such as light or sound) and their perception.
Gustav Theodor Fechner first psychophysicist
absolute threshold - the minimal amount of energy that can
produce a sensation
Ernst Weber - early psychophysicist (p.145)
difference threshold - the minimal difference in intensity which
is detectable
Just Noticeable Difference
The minimal amount by which a
source of energy must be increased or decreased so that a difference in
intensity will be perceived.
jnd
Signal Detection Theory
The view that the perception of
sensory stimuli involves the interaction of physical, biological, and psychological
factors.
Sensory Adaptation (p.146)
The processes by which organisms become more sensitive to stimuli that
are low in magnitude and less sensitive to stimuli that are constant or ongoing
in magnitude.
Sensitization- becoming more sensitive to stimuli that are low in
magnitude.
Desensitization - becoming less sensitive to constant stimuli.
Vision & Light
Light is the
part of the electromagnetic spectrum that stimulates the eye and produces
visual sensations.
See the
electromagnetic spectrum on p.148.
Light travels
in waves, with wavelengths.
Visible
light: 400 to 700 nanometers
Roy G. Biv
Parts of the Retina
Photoreceptors (Rods & Cones)
Cones - color cells (6.5 million)
Rods - Black & White/ Low light (125 million)
Bipolar Cells
Ganglion Cells - form Optic Nerve
Color Vision: The Basics
Hue
- the color of light, as determined by its
wavelength
Amplitude - the size of the wave; determines brightness or
intensity
Saturation - the degree of purity of a color
The Color Wheel (See Fig. 4.6, p. 151.)
complementary - opposite on the wheel
analogous - similar colors, next to each other
Theories of Color Vision
Trichromatic Theory
- see p.153; also known as the Young-Helmholtz
Theory
three types of
cones
red sensitive
green sensitive
blue sensitive
supported by microspectrophotometry
Opponent Process Theory
Proposed by Ewald Hering in 1870
three types of
receptors:
red-green
blue-yellow
light-dark
explains retinal
afterimages.
See page 153.
Color Blindness
Monochromat
- a person who is totally color blind and is sensitive to black and white
only.
Dichromat - a person who is sensitive to black/white and either red/green
or blue/yellow and hence partially color blind.
Trichromat - a person (or
a mouse!) with normal color vision.
Visual Perception
Top-Down Versus Bottom-Up Processing
Top-down
processing
Use of
contextual information or knowledge of a pattern in order to organize parts of
the pattern
Bottom-up
processing
Organization
of the parts of a pattern to recognize the pattern they compose
Gestalt rules of Visual Perception
Figure - Ground
Closure
proximity-nearness
similarity
continuity
Perception of Motion
Autokinetic effect
Stroboscopic
motion
Phi phenomenon
Monocular Cues for Depth
Perspective
interposition
texture gradient
shadowing
motion parallax
See p. 160.
Binocular Cues for Depth
Convergence
- based on the inward movement of the
eyes as they attempt to focus on an object that is drawing nearer.
Retinal
Disparity - based on the difference in
the image cast by an object on the retinas of the eyes as the object moves
closer or farther away.
Perceptual Constancies
Size constancy
Shape constancy
Color constancy
Brightness
constancy
Kinesthesis
The
sense that informs us about the positions and motion of parts of our bodies.
From
the Greek word for motion, (kinesis) and perception (aisthesis).
The sense of equilibrium that
informs us about our bodies positions relative to gravity.
Made possible by the semicircular
canals of the inner ear.
See page 173.