The Visual System

The Awareness Test Just for fun, let’s test your awareness of your surroundings…

How do we see? No light? No sight! light enters the eye as waves of electromagnetic energy light enters the eye as waves of electromagnetic energy length of the wave determines a light’s color length of the wave determines a light’s color the height of the wave (amplitude) determines brightness the height of the wave (amplitude) determines brightness

Structure of the Visual System

Optic Nerve (1) nerve that carries visual information from the eye to the occipital lobes of the brain nerve that carries visual information from the eye to the occipital lobes of the brain

Blind Spot (2) where the optic nerve exits the eye where the optic nerve exits the eye no rods and cones at this point, so there is a small blind spot in vision (pg. 166) no rods and cones at this point, so there is a small blind spot in vision (pg. 166)

Retina (3) has cells that convert light energy to nerve impulses has cells that convert light energy to nerve impulses made up of three layers of cells: made up of three layers of cells: Receptor cells Receptor cells Bipolar cells Bipolar cells Ganglion cells Ganglion cells

Receptor Cells sight - change light into neural impulses the brain can understand sight - change light into neural impulses the brain can understand visual system has two types of receptor cells – rods and cones visual system has two types of receptor cells – rods and cones

Rods only detect,, and shades of gray only detect black, white, and shades of gray

Cones detect sharp images and color detect sharp images and color cluster at the fovea cluster at the fovea

Bipolar Cells middle layer of retina middle layer of retina gather information from rods & cones and pass it on to the ganglion cells gather information from rods & cones and pass it on to the ganglion cells

Ganglion Cells axons of ganglion cells form the optic nerve axons of ganglion cells form the optic nerve blind spot is created where optic nerve exits the eye (page 166) blind spot is created where optic nerve exits the eye (page 166)

Cornea (4) outside layer on the front of the eyeball outside layer on the front of the eyeball two tasks: two tasks: focuses light by bending it toward a central focal point focuses light by bending it toward a central focal point protects the eye protects the eye

Pupil (5) opening in center of eye opening in center of eye controls amount of light entering the eye (surrounded by the iris) controls amount of light entering the eye (surrounded by the iris)

Iris (6) colored portion of the eye colored portion of the eye regulates the size of the pupil by changing its size - allowing more or less light to enter the eye regulates the size of the pupil by changing its size - allowing more or less light to enter the eye

Lens (7) focuses the image on the back of the eye (retina) focuses the image on the back of the eye (retina) muscles that change the thickness of the lens change how the light is bent thereby focusing the image muscles that change the thickness of the lens change how the light is bent thereby focusing the image

Fovea central focal point of the retina central focal point of the retina spot where vision is best (most detailed) spot where vision is best (most detailed)

Color Vision Theories

Trichromatic (three-color) Theory cones are “tuned” to be sensitive to red, green & blue wavelengths of light cones are “tuned” to be sensitive to red, green & blue wavelengths of light all the colors we see are a combination of these three colors all the colors we see are a combination of these three colors

Color Deficient Vision people who lack one of the three types of cones people who lack one of the three types of cones usually the red or green receptors are missing usually the red or green receptors are missing inherited & found more in males inherited & found more in males

Opponent-Process Theory of Color color-processing neurons oppose one another: color-processing neurons oppose one another: red – green red – green yellow – blue yellow – blue black – white black – white light that stimulated one half of the pair inhibits the other half light that stimulated one half of the pair inhibits the other half

Hearing

Sound sound comes in waves that are produced by vibration sound comes in waves that are produced by vibration

The Structure of the Auditory System

Auditory Canal (6) opening where sound waves enter the ear for processing opening where sound waves enter the ear for processing

Tympanic Membrane/Eardrum (7) transfers sound vibration from the air to the ossicles transfers sound vibration from the air to the ossicles

Tympanic Membrane (w/ tear)

Ossicles three tiny bones that transfer sound waves from the eardrum to the cochlea three tiny bones that transfer sound waves from the eardrum to the cochlea hammer (5) hammer (5) anvil (4) anvil (4) stirrup (3) stirrup (3)

Ossicles – Hammer, Anvil, Stirrup

Oval Window receives sound vibration from the ossicles receives sound vibration from the ossicles vibrates the fluid in the cochlea vibrates the fluid in the cochlea

Cochlea (2) where sound waves are changed into neural impulses where sound waves are changed into neural impulses filled with fluid filled with fluid

Cochlea

Hair Cells receptor cells in the cochlea that change sound vibrations into neural impulses receptor cells in the cochlea that change sound vibrations into neural impulses

Hair Cells

Semicircular Canals used in sensing body orientation and balance (vestibular sense) used in sensing body orientation and balance (vestibular sense) relies on fluid in the canals relies on fluid in the canals

Auditory Nerve (1) formed by fibers at the base of each hair cell formed by fibers at the base of each hair cell nerve that carries sound from the ears to the temporal lobes nerve that carries sound from the ears to the temporal lobes

How can we tell the difference between different sounds? 3 Theories: 3 Theories: place theory place theory volley theory volley theory frequency theory frequency theory

Place Theory of Hearing different types of sound waves vibrate different locations/places on the cochlea different types of sound waves vibrate different locations/places on the cochlea high sounds vibrate one area, low sounds another high sounds vibrate one area, low sounds another problem: very low sounds cause entire cochlea to vibrate problem: very low sounds cause entire cochlea to vibrate

Frequency Theory of Hearing frequency with which the cochlea is vibrated tells us what sound we hear frequency with which the cochlea is vibrated tells us what sound we hear problem: cannot explain how we tell the difference between high-pitched sounds (neurons can only fire so fast) problem: cannot explain how we tell the difference between high-pitched sounds (neurons can only fire so fast)

Volley Theory of Hearing sensory neurons in the cochlea (the hair cells) fire in groups, as volleys sensory neurons in the cochlea (the hair cells) fire in groups, as volleys pattern of firing allows us to tell the difference between sounds pattern of firing allows us to tell the difference between sounds

Sensation

Sensation awareness of the world awareness of the world process where our sensory systems & nervous system receive stimuli from the environment process where our sensory systems & nervous system receive stimuli from the environment

Perception interpretation of sensory information interpretation of sensory information process of organizing & interpreting sensory information process of organizing & interpreting sensory information

Two ways we process information: 1. bottom-up processing analyze the raw material entering through the eyes, ears, etc. analyze the raw material entering through the eyes, ears, etc. 2. top-down processing focus on expectations & experiences in interpreting sensory information focus on expectations & experiences in interpreting sensory information

Interpret this Sensory Information… I’m going to Fl --- for spring break. I’m going to Fl --- for spring break. “Daylight savings time ends tomorrow, and so people should remember to change their …” “Daylight savings time ends tomorrow, and so people should remember to change their …” “ ” “ ”

Perception in Action How do you interpret this sensory information?

Top-down or Bottom-up? Example (don’t write this ) Identify an unknown object based on elements of sensation: Identify an unknown object based on elements of sensation: red sphere red sphere cool, hard surface cool, hard surface fits comfortably in your hand fits comfortably in your hand pleasant aroma pleasant aroma satisfying crunch when bitten satisfying crunch when bitten tastes both sweet and tart tastes both sweet and tart Analysis of this data leads to the perception that the unknown object is an _________________. Analysis of this data leads to the perception that the unknown object is an _________________.

Top-down or Bottom-up? Example (don’t write this either) Would the descriptions below be processed top-down or bottom- up? Explain. Would the descriptions below be processed top-down or bottom- up? Explain. red sphere red sphere cool, hard surface cool, hard surface fits comfortably in your hand fits comfortably in your hand pleasant aroma pleasant aroma satisfying crunch when bitten satisfying crunch when bitten tastes both sweet and tart tastes both sweet and tart What types of sensations would you experience when eating the food pictured to the right? What types of sensations would you experience when eating the food pictured to the right?

Illusions Module 10: Perception

Illusions misinterpreting sensory stimuli misinterpreting sensory stimuli help researchers understand how sensation and perception normally works help researchers understand how sensation and perception normally works

Müller-Lyer Illusion

Most people think segment AB equals BC. In reality AB is much longer than BC. Theory: we have learned to interpret arrowheads at the ends of a line as an indication of distance

Müller-Lyer Illusion

Ames Room Photos explain the photos at the top of page 200 explain the photos at the top of page 200 video Segment: “Ames Room Illusion Explained” video Segment: “Ames Room Illusion Explained”

Ames Room Illusion: Secret Revealed