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





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?


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


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


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.