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Sensations and PerceptionsChapter 4

+Sensations and Perceptions

Sensation- the process by which a stimulated receptor (such as eyes or ears or other senses) creates a pattern of neural messages that brain interprets. Sensation represents the first series of steps in processing incoming information.

Perception- a mental process that elaborates and assigns meaning to the incoming sensation patterns.

+How does stimulation become sensation?

Core Concept: The brain senses the world indirectly because the sense

organs convert stimulation into the language of the nervous system: neural impulses

+How does stimulation become sensation?

Our senses have adaptive functions. They aid our survival by directing us towards certain stimuli that help us to live such as foods we like and seeking shelter.

Our senses also help us to find pleasure in things like the arts, athletics, and relationships.

How do our senses do all of this? The brain senses the world indirectly because the sense

organs convert stimulation into the language of the nervous system: neural messages.

+How does stimulation become sensation?

The brain never receives stimulation directly from the outside world, it must rely on secondhand information from the go-between sensory system, which delivers only coded neural messages, out of which the brain must create its own experiences.

Example: You can’t receive phone messages without a telephone receiver to convert the electronic energy into sound you can hear. Your brain needs sensory system to convert the stimuli from the outside world into neural signals that it can comprehend.

+3 Attributes common to all senses.

1. Transduction

2. Adaptation

3. Thresholds

+Transduction: changing stimulation into sensation.

Is the term used for the sensory process that converts physical energy, such as light or sound waves into the form of neural messages.

Transduction begins with the detection by a sensory neuron of the physical stimulus (such as the sound wave made by a vibrating guitar string). When the appropriate stimulus reaches a sense organ, it activates a specialized neuron (receptor) which respond by converting their excitation into a nerve signal.

Neural impulses carry a code of the sensory event in a form that can be further processed by the brain. (The only thing that continues on into the nervous system is information)

+Sensory Adaptation

Main role of our stimulus detectors is to announce changes in the external world. Clap of Thunder

Sensory adaptation: the great quantity of incoming sensations would quickly overwhelm us if not for this.

Is the diminishing responsiveness of sensory systems to prolonged stimulation. Unless it is quite intense or painful, stimulation that persists without changing in intensity usually shift to the background of our present awareness. Ex- Background music you hear in stores while shopping is

usually played so often you can’t remember the songs, but if someone was playing Christmas music in the summer you would remember.

+Thresholds

Absolute Thresholds- The amount of minimal stimulation necessary for a stimulus to be detected. Example: If you point out a faint star to a friend, but he cannot

see it. The stars light is above your absolute threshold (you can see it) but below his.(cannot see it)

Difference Thresholds- the smallest physical difference between two stimuli that can recognized as a difference.(JND) Ex- You are relaxing by watching TV, but your sibling is

studying. She asks you to turn down the TV, but you don’t want to but feel you should make some effort. If you turn it down as little as possible, your sibling might think you haven’t turned it down enough but you might be able to hear the difference.

+Thresholds

The minimal amount of change in the signal that is still recognizable is the– Just Noticeable Difference (JND)

JND and Difference Threshold are used interchangeably by psychologist.

+Thresholds

Weber’s law – The JND is always large when the stimulus intensity is high, and small when the stimulus intensity is low

Fechner’s law – S = k log R

S = sensation

R = stimulus

k = constant that differs for each sensory modality

+Thresholds

Steven’s power law – S = kla

S = sensation

k = constant

l = stimulus intensity

a = a power exponent that depends on the sense being measured

+Signal Detection Theory

Explains how we detect “signals” consisting of stimulation affecting our eyes, ears, noses, skin, and other sense organs.

Signal detection theory says that sensation is a judgment that the sensory system makes about incoming stimulation. Often it occurs outside of consciousness. Example: You are less likely to hear your name being called

in a crowded, loud, busy, hallway then you are in a quiet classroom.

+Signal Detection Theory

1. Stimulus Event

2. Neural Activity

3 Comparison with personal Standard

4. Action or No Action

+Subliminal Persuasion

Studies have found that subliminal words flashed briefly on a screen can “prime” a person’s later responses

No controlled research has ever shown that subliminal messages delivered to a mass audience can influence people’s buying habits

+How Are the Senses Alike? How Are They Different?

Core concept: The senses all operate in much the same way, but each extracts different information and sends it to its own specialized processing region in the brain.

+How are senses alike/different?

Vision, hearing, smell, taste, touch, pain, body position: in a sense are all the same. They transduce stimulus into energy into neural impulses. They provide us with information about the world—but how are they different?

With the exception of pain, each sends the information it extracts to a different part of the brain.

Different sensations occur because different areas of the brain become activated.

+Vision

The eye is a camera the brain uses to make motion pictures of the world.

The eye gathers light, focuses it, converts it to neural signals, and sends these signals on their way to to be processed.

What makes the eye different from other sense organs is its ability to extract the information from the light waves and then turn the characteristics of the light into neural signals the brain can process.

+Vision

The transduction happens in the retina. The light sensitive layer of cells at the back of the eye that acts much like the light-sensitive chip in a camera.

The real work in the retina is done by light sensitive cells known as photoreceptors. They operate much like tiny pixel receptors in a digital camera.

These photoreceptors consist of two types of specialized neuron—rods and cones. They absorb light energy and respond by creating neural impulses

+Rods and Cones

Rods- 125 million rods “see in the dark” that is the detect low intensities of light at night. Help you find a seat in a dark movie theater.

Cones- Making the fine distinctions necessary for color vision is the job of 7 million cones that come into play in bright light. Each one is specialized to detect the light waves we either sense as blue, red, or green. The cones concentrate in the very center of the retina, in a small region, called the fovea.

Fovea- gives us our sharpest vision. We usually use or fovea when scanning to focus on whatever interests us most.

+Anatomy of Visual Sensation

Photoreceptors – Light-sensitive cells in the retina that convert light energy to neural impulses

Rods – Sensitive to dimlight but not colors

Cones – Sensitive tocolors but not dim light

Fovea – Area of sharpest vision in the retina

+Cells in the retina

These cells are vital to vision, but they do not respond directly to light.

Bipolar cells- have the job of collecting impulses from many photoreceptors(rods and cones) and shuttling them on to the ganglion cells which takes them to their other destinations.

Bundled together, the axons of ganglion cells make up the optic nerve. Which transports visual information from the eye to brain.

Your visual system carries no light at all beyond the retina, only patterns of nerve impulses conveying information derived from incoming light.

+Blind Spot

A small area of the retina in each eye where everyone is blind, because that part of the retina has no photoreceptors.

It is located at the point where the optic nerve exists in each eye. If you vision is normal, you do not experience blindness there because what one eye misses is registered by the other eye and the brain “fills in” the spot.

+Anatomy of Visual Sensation

Optic nerve – Bundle of neurons that carries visual information from the retina to the brain.

Blind spot – Point where the optic nerve exits the eye and where there are no photoreceptors

+Processing Visual sensations in the brain

We look with our eyes, but see with our brain.

In order to do this, we use the visual cortex in our brain. The brain begins working its magic by transforming the

incoming neural impulses into visual sensations of color, form, boundary and movement. The visual cortex also takes the 2-dimensonal patterns from each eye and assemble them into a 3 dimensional world of depth.

With further processing the cortex combines these visual sensations with memories, motives, emotions, and sensations to create a visual representation of the world and our interests.

+Brightness

Brightness comes from the intensity of amplitude of light, determined by how much light reaches the retina.

Bright light, coming from an approaching cars headlights, involves a more intense light wave, which creates neural activity in the retina, whereas dim light from your car’s instrument panel does not.

+Color

Color (hue)- is not a property of things in the external world, rather its is a psychological sensation created in the brain from information obtained by the eyes from the wavelength of visible light.

Color is the SENSATION that the brain creates based on wave lengths of light striking our eyes.

The eyes detect the special form of energy we call visible light. The light we can see occupies a tiny segment of the cast electromagnetic spectrum. Our only access into the spectrum comes from the visible spectrum

+Terms

Electromagnetic Spectrum- Entire range of electromagnetic energy, including radio waves, X-rays, microwaves, and visible light.

Visible Spectrum- Tiny part of the electromagnetic spectrum to which our eyes are sensitive.

+Transduction of Light in the Retina

+Two ways of sensing color

Color is realized in the cortex, but begins in the retina.

Three different types of cones sense different parts of the visible spectrum.

Trichromatic theory- idea that colors are sensed by 3 different types of cones sensitive to light in the red, blue, and green wave lengths.

Opponent-Process Theory- idea that from the bipolar cells onward the visual system processes colors in either complimentary pairs.

+How the Visual System Creates Brightness

Wavelength Color

Intensity-Brightness

+Color Blindness

Total inability to distinguish colors.

Most people just have a problem in distinguishing color in low light situations. It is rare to have full color blindness.

+Hearing

The Physics of Sound Frequency –

Number of cycles completed by a wave in a given amount of time

Low Frequency High Frequency

+Hearing

The Physics of Sound: Amplitude –

Physical strength of a wave

High Amplitude Low Amplitude

+Hearing

Two characteristics of physical properties of any sound wave that will determine how it will be sensed by the brain are: 1. Frequency 2. Amplitude

Frequency- refers to the number of vibrations or cycles the wave completes in a given amount of time. (cycles per second cps, or hertz)

Amplitude- a measure of physical strength of the sound wave. Measure of units- is normally pressure or energy. Ex- when your turn down the volume, you are decreasing the

amplitude of sound waves.

+How we hear sound waves

Like vision, sensation of sound requires that waves be transduced into neural impulses and sent to the brain. This happens in 4 steps.

1. Airborne sound waves must be relayed to the inner ear. Vibrating waves of air enter the outer ear (pinna) and strike

the eardrum (tympanic membrane). This tightly stretched sheet of tissue transmits the vibrations to 2 tiny bones; hammer, anvil, stirrup (named for their shape). These bones immediately pass the vibrations on to the primary organ of hearing, the cochlea, located in the inner ear.

+Steps of hearing

Step 2: The cochlea focuses the vibrations on the basilar membrane (a thin strip of tissue sensitive to vibrations in the cochlea the membrane contains hair cells connected to neurons and once active the neurons fire.). The airborne sound waves become “Seaborne” bc the coiled tube of cochlea is filled with fluid.

Step 3: The basilar membrane converts the vibrations into neural messages. The swaying of tiny hair cells on the vibrating basilar membrane stimulates a sensory nerve ending to fire the neurons, then transform the mechanical vibrations.

+Steps of hearing

Step 4: Finally, the neural messages travel to the auditory cortex in the brain. Neural signals leave the cochlea in a bundle of neurons

called the auditory nerve. The neurons from the two ears meet in the brain stem and are passed to the auditory cortex for further higher order processing.

+How Sound Waves Become Auditory Sensations

Tympanic membrane –The eardrum

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Cochlea –Where sound waves are transduced

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+How Sound Waves Become Auditory Sensations

Auditory nerve –Neural pathway connecting the ear and the brain

+Psychological Qualities of Sound

How do we distinguish one sound from another?

1.Pitch

2. Loudness

3. Timbre

+Pitch

A sound waves frequency determines the highness or lowness of a sound.

High frequencies produce high pitch and low frequencies produce low pitch.

+Loudness

Loudness of a sound is determined by is physical strength, or amplitude.

Sound intensity is usually expressed/ measured in units called decibels. (dB)

+Timbre

The quality of a sound wave that derives from the wave’s complexity (combo of pure tones)

This is what helps you recognize a friend’s voice on the phone or distinguish btw two artists singing the same song.

+Deafness

Two types

1.Conduction Deafness

2. Nerve Deafness

Conduction deafness- the ways in which sound waves are converted to nerve energy have interrupted. In most cases damage has occurred to any of the structures of the middle of the ear.

Nerve Deafness- An inability to hear, linked to a deficit in the body’s ability to transmit impulses from the cochlea to the brain, usually involving the auditory nerve or higher auditory processing centers

+Other Senses

Position and movement: to act purposefully and gracefully, we need constant information about where our limbs and other body parts are in relation to each other and objects in the environment.

The physical mechanisms that keep track of body position, movement, and and balance are composed of 2 different systems.

1. Vestibular Sense- orients us with respect to gravity. Also tells us when we are moving or how our motion is changing.

2. Kinesthetic Sense- Sense of body position and movement of body parts relative to each other

+Smell

Or Olfaction, involves a chain of biochemical events.

First odors interact with receptor proteins associated with specialized hairs in the nose. The stimulated nerve cells associated with these hairs convey information about the stimulus to the brain olfactory bulbs, where sensations of smell are realized. These bulbs can be found under the frontal lobe.

+Smell

Olfaction –Sense of smell

Olfactory bulbs –Brain sites of olfactory processing

Pheromones –Chemical signals released by organisms to communicate with other members of the species.

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+Taste: Gustation

Also based on chemistry. Works together with smell.

Gustation- sense of taste. Has 4 qualities– sweet, sour, bitter, and salty. A 5th one has been added Umami found in Asian cuisine.

The taste receptor cells are gathered in taste buds, located on the top and side of the tongue, where they can easily sample molecules in our food and drink. These receptors cluster in small mucous membrane projections called papillae.

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+Skin Sense

Protects us against surface injury, holds in body fluids, and helps regulate body temperature.

Skin also contains nerve endings that when stimulated by contact with external objects, produce sensations of touch, warmth, and cold.

These skin senses are connected to the somatosensory cortex and located in the parietal loves.

How does touch effect us?

+Pain

Can arise from intense stimulation of various kinds, such as a very loud noise, heavy pressure, or an extremely bright light.

Pain is not merely a result of stimulation. Phantom limb- sensations arise in the brain itself. People

missing limbs still can feel pain in those limbs.

+The Gate- Control Theory

An explanation for pain control that purposes we have a neural “gate” that can, under some circumstances block incoming pain signals.

READ ABOUT THIS!

+Dealing with pain

Threshold of pain varies enormously from person to person.

Many people can learn how to control pain through techniques.

+Relationship btw sensation and perception

Perception brings meaning to sensation, so perception produces an interpretation of the world, not a perfect representation of it.

A percept is what we perceive. A meaningful product of what we percieve. Often an image

that has been associated with concept, memories, of evens, emotions, and motives.

+Feature Detectors

To help us make perceptual judgments, our brains must have specialized groups of cells dedicated to the detection of specific stimulus features. Such as, length, slant, color.

There is even a part in the occipital lobe containing cells that are especially sensitive to features of the human face—feature detectors

We still don’t know how the brain manages to combine (bind) the multiple features it detects into a single percept (like a face) This is called the “binding problem”

+Bottom-Up and Top-Down Processing

Perception always involves taking sensory data into the system through receptors and sending it “upward” to the cortex, where basic analysis, involving the feature detectors, is first performed to determine the characteristics of the stimuli.

Is it loud, sweet, painful, pleasant smelling? These characteristics are how we determine what we finally perceive as an object or event.

+Top Down

Invokes a perceiver’s goals, past experience, knowledge, expectations, memory, motivations, or cultural background in the interpretation of an object or event.

Will that help me get my degree? Is she conservative or liberal?

Perceptual Constancy- the ability to recognize the same object as remaining “constant” under different conditions, such as changes in illumination, distance, or location.

+Perceptual Constancies

Perceptual constancy – Ability to recognize the same object under different conditions, such as changes in illumination, distance, or location

+Perceptual Ambiguity and Distortion

Illusions – Demonstrably incorrect experience of a stimulus pattern, shared by others in the same perceptual environment

Ambiguous figures – Images that are capable of more than one interpretation

+Theoretical Explanations for Perception

Learning-based inference –View that perception is primarily shaped by learning, rather than innate factors

Perceptual set –Readiness to detect a particular stimulus in a given context

+The Gestalt Approach

Gestalt psychology – View that much of perception is shaped by innate factors built into the brain

Figure – Part of a pattern that commands attention

Ground – Part of a pattern that does not command attention; the background

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Subjective contours – Boundaries that are perceived but do not appear in the stimulus pattern

Closure – Tendency to fill in gaps in figures and see incomplete figures as complete

+The Gestalt Laws of Perceptual Grouping

Similarity

Proximity

Continuity

Common Fate

Prägnanz

+Law of Prägnanz

ABIRD

IN THETHE HAND