Vision- Receptors
Receptive Fields and Rod vs. Cone Visual
Acuity
o
Cones - in the
fovea, one cone
often synapse onto only a single ganglion cell
o
Rods - the axons
of many rods synapse onto one ganglion cell
o
This allows rods
to be more sensitive in dim light, but it also reduces visual acuity
Color Vision
o
Our visual system interprets differences in the
wavelength of light as color
o
Rods are color blind although they are more
sensitive to lights in the blue end of the spectrum then the red end
o
In contrast, cones can see different colors This difference occurs because we have only one type of rod
but three types of cones
Visual Information Processing
§
Trichromatic (three
color) Theory
§
Young and Helmholtz
§
three different retinal
color receptors
§
red
§
green
§
blue
Visual Information Processing
Opponent-Process Theory- opposing retinal processes enable
color vision
“ON” “OFF”
red green
blue yellow
black white
Complementary
Afterimages
Complementary
Afterimages
How the eye works
o
What happens to color in a dark room?
o
Why does your vision in a dark room improve with
time?
o
Why do police now have blue lights on top of
their cars?
o
Why do you see shadows and movements in the
periphery when walking the streets of Oakland
late at night?
Hearing: Sound Waves
o
Auditory
perception occurs when sound waves interact with the structures of the ear.
o
Sound Wave - changes over time in the pressure of an elastic medium (for example, air or water).
o
Without air (or
another elastic medium) there can be no sound waves, and thus no sound
Characteristics of Sound
o
Frequency of a sound wave is related the pitch
of a sound
o
Amplitude of a sound wave is related to loudness
of a sound
Anatomy of Ear
o
Purpose of the
structures in the ear:
n
Measure the
frequency (pitch) of sound waves
n
Measure the amplitude
(loudness) of sound waves
Major Structures of the Ear
o
Outer Ear - acts
as a funnel to direct sound waves towards inner structures
o
Middle Ear -
consists of three small bones
(or ossicles) that amplify the sound
o
Inner Ear -
contains the structures that actually transduce sound
into neural response
Coding of Sounds
How We Locate Sounds
Taste: who are the good cooks?
Perception
o
We have
previously examined the sensory processes by which stimuli are encoded.
o
Now we will
examine the ultimate purpose of sensory information
o
PERCEPTION - the
conscious representation of the external environment.
How do you know what this is?
Historical Debate and Interest
o
Consider the simple ability to perceive depth
Convergence
Binocular: Retinal Disparity
Binocular: Retinal Disparity
How do you perceive depth
Texture Gradient
o
Texture decreases
with distance
Relative Size
o
Size decreases
with distance and can be compared with known objects
Interposition: one object blocking another
Shading
o
Farther away
objects appear darker
What do you perceive
How do you know what is figure or ground?
Perceptual Organization
§
Figure and Ground--organization of the visual
field into objects (figures) that stand out from their surroundings (ground)
Perceptual
Organization: Gestalt Psychologists
§
Grouping
§
the perceptual tendency
to organize stimuli into coherent groups
§
Grouping Principles
§
proximity--group nearby
figures together
§
similarity--group
figures that are similar
§
continuity--perceive
continuous patterns
§
closure--fill in gaps
§
connectedness--spots,
lines, and areas are seen as unit when connected
Perceptual Organization:
Grouping Principles
Perceptual Organization:
Closure
§
Gestalt grouping principles are at work here.