Chapter 4!

The Visual System:Essentials of sight

Light- a form of electromagnetic radiation that travels like a wave

Amplitude- the height within the wavelength◦ Mainly affects perception of brightness

Wavelength- distance between peaks◦ Affects the perception of color

Purity- how varied the mix is between the two◦ Influences the perception of the saturation

(richness) of colors

The Stimulus: Light

Refers to the whiteness that is in the color Whiteness declines=saturation increases Most objects don’t omit light; the reflect it

Saturation

Only including wavelengths that people can see

There are so many more, visual spectrum is only a small portion

What is light?

Insects- ultravioletFish/reptiles- infrared

Two main purposes:◦ Channel light into neural tissue that receives it

(retina)◦ Houses the retina

Cornea- transparent “window” and the lens behind it form upside down image of objects then image is adjusted

Lens- transparent eye structure that focuses the light rays falling on the retina

The eye: A living optical instrument

Accommodation◦ Lens making adjustments that facilitate is called

accommodation◦ Occurs when curvature of lens adjusts to alter

visual focus Nearsightedness

◦ Close objects are clear; far objects blurry

Farsightedness◦ Far objects are seen clearly; close objects are blurry

Iris- the colored ring of muscle surrounding the pupil

Pupil- opening in the center of the iris that helps regulate the amount of light that passes through to the rear chamber of the eye

pupil

Retina- neural tissue lining the inside back surface of the eye- absorbs light- processes images- sends visual information to the brain

optic disk- fibers (axons) diving into a hole behind the retina

Blindspot- the hole that the optic disks creates in the retina

The Retina: the brain’s envoy in the eye

Cones- specialized visual receptors that play a key role in daylight vision and color vision

Visual acuity- sharpness and precise detail Fovea- tiny spot in the center of the retina

that contains only cones- greatest visual acuity

Rods- specialized visual receptors that play a key role in night vision and peripheral vision- more sensitive

Visual receptors

Dark adaptation◦ processes in which the eyes become more

sensitive to light in low illumination◦ 30 minutes

Light adaptation◦ process in which lightbecomes less sensitive to light in high illuminations

Dark and light adaptation

Optic nerve- collection of axons that connect the eye to the brain

Receptive field- retinal area that when it is stimulated affects the firing of that cell

Information processing in the retina

Light falls on the eye, but you see with your brain.

The retina does a lot of information processing for a sensory organ, visual input is meaningless until it is processed in the brain.

Vision and the Brain

Optic Chiasm- The point at which the axons from the inside half of each eye cross over then project to the opposite half of the brain.

Visual information gets to the brain by axons leaving the back of each eye form the optic nerves, then traveling to the optic chiasm. This insures that signals from both eyes go to both hemispheres of the brain.

After reaching the optic chiasm. They split into two pathways one leading to the thalamus. This is considered the main pathway where about 90% of axons from the retinas synapse in the lateral Genicualte nucleus (LGN)

Visuals signals are processed in the LGN and then distributed to areas in the occipital lobe making up the primary visual cortex.

Visual Pathways to the Brain

Visual input ultimately arrives in the primary visual cortex located in the occipital lobe.

David Hubel and Torsten Wiesel identified three major types of visual cells in the cortex which were called simple cells, complex cells, an hypercomplex cells.

THe key point of all this is that the cells in the viual cortex seem to be highly specialized. They have been characterized as Feature Detectors.

Feature Detectors- Neurons that respond selectively to very specific fetures of more complex stimuli.

After visual input is processed in the primary visual cortex, it is often routed to other cortical areas.

Info. Processing in the Visual Cortex

After this they travel to one of two streams The ventral stream (what) or dorsal stream (where).

These are known as the what, where streams. As signals move farther along in the visual

processing system, neurons become even more specialized or fussy about what turns them on, and the stimuli that activate them become more and more complex.

“Grandmother cell” was to be humorous but it is the idea that certain cells react to the visual image of certain people.

Continued..

The lights people see are mixtures of different wavelengths. Perceived color is primarily a function of the dominant wavelength in these mixtures.

Lights with the longest wavelengths appear red, whereas those with shortest appear violet.

Most of the diverse variations are the result of mixing a few basic colors, there are two kinds of color mixtures: subtractive and additive.

Subtractive- color mixing works by removing some wavelengths of light, leaving less light than was originally there.

Additive- color mixing works by superimposing lights, putting more light in the mixture than exists in any one light by itself

Viewing the World in Color

The lights people see are mixtures of different wavelengths. Perceived color is primarily a function of the dominant wavelength in these mixtures.

Lights with the longest wavelengths appear red, whereas those with shortest appear violet.

Most of the diverse variations are the result of mixing a few basic colors, there are two kinds of color mixtures: subtractive and additive.

Subtractive- color mixing works by removing some wavelengths of light, leaving less light than was originally there.

Additive- color mixing works by superimposing lights, putting more light in the mixture than exists in any one light by itself

Viewing the World in Color

the trichromatic theory of color vision was first stated by Thomas Young and later modified by Hermann von Helmholtz.

Trichromatic Theory- holds that the human eye has three types of receptors with differing sensitivities to different light wavelengths.

Helmholtz believed that the eye that had specialized receptors that were sensitive to the wavelengths associated with red, green, or blue.

Color Blindness- encompasses a variety of deficiencies in the ability to distinguish among colors.

Blindness is misleading because it is very rare to find someone to be completely blind of all colors they usually are dichromats meaning they see two of the three.

Trichromatic Theory of Color Vision

Complementary colors- are pairs of colors that produce gray tones when mixed together.

The various pairs of complementary colors can be arranged in a color circle.

Afterimage- a visual image that persists after a stimulus is removed.

the color of the afterimage will be the complement of the color you originally started at.

Opponent process theory- holds that color perception depends on receptors that make antagonistic responses to three pairs of colors.

The antagonistic processes in this theory provide plausible explanations for complementary afterimages and the need for four names to describe colors.(red, blue, green, yellow)

Continued...

Activity one- blindfold

The Visual System: Perceptual Processes

Exploring perceptual processes in vision

Perceiving Forms, Patterns, and ObjectsHow does the brain make sense of forms, objects, depth, etc.? The brain makes sense of it all through

visual perceptionsFor example.A Reversible figure is made intentionally made to be ambiguous. It is usually a drawing that is compatible with two different interpretations that can shift back and forth.

Feature Analysis: Assembling FormsWhat is Feature Analysis? It is the process of detecting specific

elements in visual input and assembling them into a more complex form

For example. A person starts with the components od a

form, such as lines, and then builds them into perceptions of objects, such as squares or triangles. (Form Perception)

Form Perception What is Form Perception? Form Perception refers to our ability to

visually perceive objects in the world in response to the patterns of light that they caste on our retinas

Feature analysis assumes that form perception involves: (1)Bottom-Up processing (2) Top- Down processing

(1) Bottom-Up ProcessingWhat is Bottom-Up processing? Bottom-Up processing is a progression of

individual elements to the whole.For example. We attend to or perceive elements by starting

with the smaller, more fine details of that element and then building upward until we have a solid representation of it in our minds.

(2) Top- Down ProcessingWhat is Top- Down processing? Top-Down processing is a progression from

the whole to the elements.For example. The is evidence that people can perceive a

word before its individual letters, a phenomenon that has to reflect top-down processing

The Visual System: Perceptual Process

Is a tendency to experience a stable perception in the face of continually changing sensory input

Your brain is able to keep an object the same far away as up close

We are able to distinguish; size, color, shape, brightness, and location

Perceptual Constancies in Vision

visual illusion- involves an apparently inexplicable discrepancy between the appearance of a visual stimulus.

Involves a misinterpretation of perception Common visual Illusions: Mueller-Lyer

Illusion, the Ponzo Illusion, and Monster Illusion

The Power of Misleading Cues: Visual Illusions

Two Lines appear different lengths Reality they are same Misperception of depth and size constancies

lead to illusion.

Muller-Lyer Illusion

Horizontal lines same length Seem different because of the vertical lines Vertical lines slant towards each other Monster Illusion Same concept and both same size

Ponzo Illusion/ Monster Illusion

Are objects that can be represented on a two dimensional drawing, but cannot be on a three dimensional drawing

First glance they look fine, but after close examination they don’t add up or actually work

One perception about hypothesis in vision is inconsistent while another would be consiten

Impossible Figures

Common Impossible Figures

Reveals about formulating hypothesis Reveal about when hypothesis is wrong Is completely subjective to what the person

sees and only certain things can be objective.

What Do Illusions Reveal About Visual Perception?

The Auditory System: Hearing

• The ability to hear what is happening around you.

• Must be processed by the brain.

Triggered by any sound producing a sensory input in the form of sound waves.

Sound waves are the stimuli starting the hearing experience.

The Auditory System: Hearing

Vibrating molecules produce sound. (Sound waves)

Sound is Characterized by the following: Amplitude Wave Length Sound Purity

The Stimulus: Sound

Amplitude: the amount of energy in a sound wave.

Wave Length: the distance from one sound wave to the next. Measured from Crest to Crest

Sound Purity: measured in “Pitch”. It is also know as the tone of the sound.

The Stimulus: Sound

Amplitude Graphs

Wave Length Graph

Wavelengths of sound are described in terms of their frequency.

Frequency◦is measured in cycles per second (Hertz)◦Higher Frequency results in higher pitch◦Lower Frequency results in lower pitch

Human Hearing Capacities

Humans can hear sounds as low as 20 Hz and as high as 20,000 Hz.

The Human ear is most sensitive around 2000 Hz.

Humans are more sensitive to a single frequency rather than a complex mixture of many separate frequencies.

Human Limits

Amplitude (Decibels)

Frequency (Hertz)

The ear is divided into three different sections that function by using different moving parts.

The External Ear-Vibration of air molecules

The Middle Ear-Vibration of movable bones

The Inner Ear- Waves in fluid

Sensory Processing in the Ear

The external ear consists of the Pinna. The Pinna is basically a cone that collects the sounds.

Sound waves are picked up by the Pinna and funneled through the auditory canal into the eardrum which is a vibrating membrane.

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Within the middle ear the vibrations of the eardrum are transmitted to vibrate 3 tiny bones in the ear (hammer, anvil and stirrup) together these bones are referred to as the Ossicles.

The Ossicles pick up small changes in air pressure.

The inner ear consists mainly of the Cochlea. The Cochlea is a fluid filled, coiled tunnel that contains receptors for hearing. The Cochlea is vibrated by the Ossicles and the signals are routed through the thalamus and auditory cortex.

There are TWO main theories of hearing and these are the Place Theory and Frequency Theory

Auditory Perception Theories of Hearing

Place Theory

•Herman Von Helmholtz theorized that a specific sound frequency would vibrate in it’s own specific manor. This in turn would cause the basilar membrane to only vibrate in specific patterns. •This would be similar to plucking a specific guitar string makes a specific pitch.

In place theory it is said that perception of pitch corresponds to the vibration of different portions or places along the basilar membrane.

It is assumed in this theory that hair cells at various locations vibrate independently by different frequencies. Then that the brain detects the different frequency according to which area is most active.

Frequency Theory holds that perception of pitch corresponds to the rate or frequency that the basilar membrane vibrates.

In this theory rather than a guitar the Basilar Membrane is compared to a drumhead.

The whole membrane is said to vibrate in response to sound

Frequency Theory

It is said that a specific frequency causes the basilar membrane to vibrate a corresponding number of times in a second. 3,000Hz would vibrate 3,000 times a second.

It has been discovered that both place and frequency theory were correct in part but both were flawed.

Place theory was correct other than the thinking that the hairs are independent. They are not and they actually move together in the way suggested by frequency theory.

The Current Theory

Pitch perception depends on both place and frequency coding of vibrations along the basilar membrane.

Sounds under 1,000Hz appear to be translated into frequency pitch.

Sounds between 1,000 and 5,000Hz appear to depend on a combo of frequency and place coding.

Sounds over 5,000 seem to depend on place coding only.

Sound Expieriment

Different Frequencies and How You ear Them

THE OTHER SENSES: TASTE, SMELL, AND TOUCH.

The Physical Stimuli for Taste: any chemical substance that dissolves in water.

Gustatory Receptors: Clusters of taste cells found in the taste buds that line the trenches around tiny bumps on the tongue.

THE GUSTATORY SYSTEM: SENSORY OF TASTE

Primary Tastes: Sweet, Sour, Bitter, and Salty

Sensory Adaptation: a gradual decline in the sensitivity to prolonged stimulation.

The Physical Stimuli for Smell: chemical substances that can evaporate into the air.

Olfactory Cilia: the receptors for the nose, hair like structures located in the upper portion of the nasal passages.

THE OLFACTORY SYSTEM: SENSORY FOR SMELL

Smell is the only sensory system that is not routed through the thalamas before it projects onto the cortex.

Oders can affect peoples moods

The Physical Stimuli for Touch: consists of mechanical, thermal, and chemical energy that comes into contact with the skin◦ Produce perceptions of tactile stimulation,

warmth, cold, and pain.

TOUCH: SENSORY SYSTEMS IN THE SKIN