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QUESTION

Jul 23, 2020

Assignment Instructions For your Midterm essay exam, you will complete 10 essay questions which focus on the course readings. Midterm essay answers must be attached as a Word document to the appropria

Assignment Instructions

For your Midterm essay exam, you will complete 10 essay questions which focus on the course readings. Midterm essay answers must be attached as a Word document to the appropriate assignment page, not typed into the assignment student comments boxes. In addition to writing a 300 word answer to each essay question with APA formatted citations and references (APA title page and reference page are required. Each question should be answered clearly and numbered) students will answer each question thoroughly and completely, providing examples where required.

Answer the questions below in your Midterm exam.

1. Describe the process of perception as a series of steps, beginning with the environmental stimulus and culminating in the behavioral responses of perceiving, recognizing, and acting.

2. Because the long axons of neurons look like electrical wires, and both neurons and electrical wires conduct electricity, it is tempting to equate the two. Compare and contrast the functioning of axons and electrical wires in terms of their structure and the nature of the electrical signals they conduct.

3. What are the two answers (one “simple” and the other “profound”) to the question, “Why is our perception of colors and details worse in dim illumination than in bright illumination?”

4. What is color constancy? Describe three factors that help achieve color constancy. What is brightness constancy? Describe the factors that are responsible for brightness constancy. Lastly, compare and contrast color constancy with brightness constancy.

5. When you walk from outside, which is illuminated by sunlight, to inside, which is illuminated by “tungsten” illumination, your perception of colors remains fairly constant. But under some illuminations, such as street lights called “sodium vapor” lights that sometimes illuminate highways or parking lots, colors do seem to change. Why do you think color constancy would hold under some illuminations, but not others?

6. What is sensory adaptation? How does it occur within the various senses? What function does sensory adaptation serve? Provide a relevant example that illustrates your point.

7. What are the characteristics of the energy that we see as visible light? Provide an example illustrating how these characteristics are expressed when someone sees a rainbow. What types of things (situations and/or objects) can interfere with these characteristics?

8. How does the eye transduce light energy into a neural message? What is the blind spot in the eye and how does it impact the transduction of light energy?

9. How is visual information processed in the brain? What are some things (situations and/or objects) which can impede visual information being processed in the brain? Please include a relevant example to illustrate your answer.

10. What theories contribute to our understanding of color vision? Discuss at least two relevant theories of color vision.

READING

WEEK-1

https://www.youtube.com/watch?v=unWnZvXJH2o

https://www.youtube.com/watch?v=R-sVnmmw6WY

READING

Introduction

Topics to be covered include:

· Sensation and perception

· Sensory processing

· Physiology-perception relationship

· Neurons

What are sensation and perception? This lesson will walk through the process of sensory processing with an overview of the parts of the process you will explore in greater detail in later lessons. The sensation and perception process is a process that involves our physical senses reacting to a stimulus in the environment (like a bee), and moving that information to the brain for analysis based on our own unique bundle of experiences and knowledge. This makes perceptions unique to each person.

Visual processes will be introduced as they pertain to sensation and perception. Why is light important in visual processing? This lesson will answer that question and discuss the route sensory information takes in the visual processing systems. One of the main actors in this process is the neuron. By the end of this lesson, you will have a better understanding of what a neuron is and what it does as a messenger, conveying signals to and from the brain.

Sensation and Perception

A girl is out in a field enjoying the warm summer sunshine and beautiful flowers with a toddler. She hears a buzzing sound, and starts to look around to place the source. She is familiar with this sound, and looks for a bee. When she finds it, she realizes it is flying toward her and she begins to run. She has been stung by a bee before, and does not want to feel that pain again. The toddler that is with her, hears the same buzzing and sees the same bee, but does not run. As a matter of fact, the toddler is curious and stands watching until the girl picks him up and moves him to a new location.

Why did the toddler have a different reaction to the bee? It has to do with perception, and the cognitive processing that occurs as information from the senses is relayed to the brain for analysis. There is quite a lot of processing that occurs in between hearing the buzzing sound and looking for a bee, and seeing the bee, identifying what it is, and moving away from it.

PRIOR KNOWLEDGE CHANGES PERCEPTION

If the information relayed to the brain matches information previously stored through acquired knowledge and experience, the brain perceives this sensory information based on what is previously stored. The toddler did not have information stored on what bees do, so she was not afraid. The girl, on the other hand, has been stung before, and has previously stored knowledge about bees. Her knowledge led to her perception of the situation. This example shows the interaction of sensation and perception.

Sensation is the process of gathering and transmitting information from the five senses: sight, hearing, taste, smell and touch. Sensation acts as a conveyor of information, but does not process the information (Goldstein & Brockmole, 2017). The information from the senses is processed by the brain as it interprets the information based on knowledge previously stored. This cognitive process is called perception (Goldstein & Brockmole, 2017). In this example, sensation occurs as the girl hears a buzzing sound and sees the bee. The information is then sent to the brain, where it is compared to information already stored in memory systems to create perception.

Processing Sensory Information

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· Bottom-up and Top-down Processing

From the beginning, the girl heard a buzzing sound. This information was relayed to the brain. The brain prompted the visual senses to search for the sound. The eyes registered the bee and sent that information to the brain. This time the brain sent the command to move away from the area. The command was based on information stored in the girl’s memory, and experiences she had previously had with a bee. The information that was relayed from the senses to the brain is called bottom-up processing (Goldstein & Brockmole, 2017). The information relayed from the brain to the rest of the body, and the recognition and review of knowledge is called top-down processing (Goldstein & Brockmole, 2017). One easy way to remember this is to think about the location of the brain, and most of the senses. Most of the senses are below the brain, so sending information to the brain would be an uphill process. The brain sits at the top of the body, for the most part, so information used by the brain would be top-down.

Vision

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The sense most people tend to rely on first is vision. The brain interprets the wavelength of light and interprets it as color. Different wavelengths of visible light represent different colors (Griggs, 2016). Shorter wavelengths appearing as blueish colors, mid-length waves appear greenish, and longer waves appear as red, orange and yellow hues (Goldstein & Brockmole, 2017). The wavelength determines color and the amplitude determines the intensity (Griggs, 2016). The wavelength is measured as the distance between wave crests and amplitude is measured by the height of each crest (Griggs, 2016). The number of waves that pass in one second in the frequency.

Visible light is the range of electromagnetic radiation that humans can see, from about 400 to 700 nanometers of wavelengths. The rest of the electromagnetic spectrum is invisible to the human eye (Goldstein & Brockmole, 2017).

Neurons

· MESSAGE TRANSPORTERS

· PARTS OF A NEURON

· SPECIALIZATION OF NEURONS

· HOW A MESSAGE TRAVELS

Let us look at how the message travels through a neuron. The dendrites receive the message from other neurons. They then send the information to the soma. The soma receives the messages from the other neurons and moves them to the axon. The axon carries a message from the soma to the terminal branches that will move the message on to the next neuron in the communication network. The message moves down the axon through an electrical current. The message moving through the axon is called the action potential (Goldstein & Brockmole, 2017).

Action Potential

When a message travels through a neuron it is based on an electrical charge. When an axon is at rest, meaning a message is not traveling through it, the electric charge inside the axon is more negative than positive. This is called resting potential. When a signal for a new message occurs, the charge inside the axon reverses to a positive electrical charge. This signal and the change in electrical charge is the action potential. Once the signal passes the axon and moves to the terminal branches, the charge inside the axon returns to a negative status and as long as a new signal is not coming through, the axon returns to resting potential (Goldstein & Brockmole, 2017). An action potential response is an all or nothing response. Once it begins it does not stop until the message signal has moved through the axon.

The electrical charge of the signal would remain the same size throughout its passage in the axon). This is called a propagated response. There is a limit to how many responses can move through the axon during a period of time. There is an interval between signals, which is called a refractory period (Goldstein & Brockmole, 2017).

Neurotransmitters

Now that we have talked about what happens in a neuron as the signal passes from the dendrites to the terminal branches, let’s talk about what happens as the signal passes from one neuron to the next. Neurons do not touch each other. There is a small gap between each neuron called the synapse, or synaptic gap. As you can imagine, this gap is extremely small. Yet, the charge does need to pass through this gap to get to the next neuron. This is where chemical action comes into play. When an electric signal reaches the end of a terminal branch, a chemical process occurs that allows the signal to move across the synapse using neurotransmitters (Goldstein & Brockmole, 2017).

Neurotransmitters are used to transport the signal from the terminal branches through the synapse and docking on the next neuron at the dendrites. As you can see, we have both an electrical action within the neuron, and a chemical reaction to cross from one neuron to the next.

Neurotransmitters, like neurons themselves, are very numerous and very specific. Certain neurotransmitters are used to send certain messages across the gap. They come in different shapes and when they move across the synapse to the next neuron they fit in to specific shapes docks on the next neuron on its receptor site (Goldstein & Brockmole, 2017). This helps to maintain the specialization of the message. For example, the message from the girl’s ears about the buzzing would likely have used a different neurotransmitter than a message about the color of a flower. When the signal from the transmitter encounters the correct receptor site, it sets off the electrical signal that again runs through the neuron starting with the dendrite and moving through the neuron to terminal branch. The signal then releases the same type of neurotransmitter as it did in the previous neuron to cross the synapse to the next neuron in the network.

There are two different types of responses to receptor sites based on the type of neurotransmitter released, and the nature of the receptor site targeted by it. The two responses are excitatory and inhibitory. The excitatory response occurs as the inside of the neuron becomes more positive, ultimately triggering action potential. This process is called depolarization, which occurs as the change in the charge moves from very negative to positive. The excitatory response triggers increasing rates of nerve firing (Goldstein & Brockmole, 2017).

Think about what might happen if the girl moves away from the bee and it continues to follow her. Her reaction would become more excited, and the nerve firing would reflect this. Once the bee moves off in a different direction, the girl would calm down, and the nerve firing would be greatly reduced. As the girl calms down and stands still, the messages would be reduced. An inhibitory response would occur as the inside of the neuron becomes more negative, decreasing the likelihood of an action potential (Goldstein & Brockmole, 2017). Thus, information is processed as it travels through the neurons. When the information is urgent, like the bee chasing the girl, the neurons move with urgency. When the bee is gone and girl calms down, the neurons reduce the need for excitement and reaction.

Neural Convergence

· From the lens, the light reaches the retina, which is the light-sensitive part of the eye that engages in the transduction process for vision. The retina has three layers of cells: ganglion, bipolar and receptor cells. The ganglion cells receive the light waves first, passing them through to the bipolar cells, and then finally to the receptor cells. The receptor cells consist of rods and cones. The rods are responsible for dim light and colorless vision, while the cones are responsible for brighter light and color (Griggs, 2016). There are many more rod cells than cone cells. Remarkably varied, rods and cones are distributed differently over the surface of the retina. The fovea is where our vision is best and we only have cones. The peripheral retina is the part of the retina outside of the fovea area and contains both cones and rods.

The outer segments of the rod and cones contain light-sensitive chemicals called visual pigments that react to light and trigger electrical signals (Goldstein & Brockmole, 2017). These signals emerge from the back of the eye through the optic nerve (Goldstein & Brockmole, 2017). The information is then passed to the optic nerve via the ganglion cells where it begins processing in the brain (Griggs, 2016).

Referring back to the example of the girl seeing the bee; light enters the outermost layer, the cornea, then passes through to her pupil, the opening at the center of the iris, the lens enables her to focus on the bee from a distance as it flies closer to her (Goldstein & Brockmole, 2017). Sending electrical “messages,” the girl’s retina translates light into nerve signals allowing her to detect the colors of the bee, yellow and black. Located in the back of the retina are her visual receptors, the cones allow the girl to see the details and colors of the bee, while the rods, which are far more numerous than cones, do not play a significant role in seeing the bee because it is daylight.

Neurons

· MESSAGE TRANSPORTERS

· PARTS OF A NEURON

· SPECIALIZATION OF NEURONS

· HOW A MESSAGE TRAVELS

We have a basic understanding of visual and auditory information processes, but what transports the message from the sensory organs to the brain and from the brain to the rest of the body? Signals are sent via neurons. Neurons are cells capable of transmitting information. Each neuron is specialized to transmit certain types of information. There are vast networks of complex circuits made up of billions of neurons in thousands of neuron networks throughout the body. Neurons communicate with other neurons with like specializations. Thus, neurons that specialize in identifying what a sound is through vision would communicate with each other. As you can imagine, the messages travel through the sensory organs and brain systems very quickly. If you think about how long it would take for a girl to hear buzzing, then look for the bee, identify the bee and move away, you can see how quickly the numerous neural messages move.

· Reception and Transduction

In this example, the visual receptors respond to the light reflected from the bee to the girl’s eyes (Goldstein & Brockmole, 2017). Each sense has sensory receptors, which are cells that respond to the different types of energy that transmit information in the environment, like the sound and light waves from the bee. The auditory receptors were also in effect, because the girl’s ears picked up the sound of the buzzing before the girl saw the bee. With visual receptors, light energy is transformed into electrical energy as the visual pigments react to the light. This process is called transduction. Transduction occurs as information from the senses is translated into a message sent to the brain. The message is sent via specialized neural networks that transmit the sensory information from the sensory receptors (Goldstein & Brockmole, 2017). Information that is transmitted through the neural networks is coded, or converted to a form of information that travels the neurons to the brain. While the signals change as they move from the initial reception of auditory and visual sensory stimuli, the electrical signals ultimately become a conscious experience based on the perception of the bee in the recognition of what it is (Goldstein & Brockmole, 2017). Recognition is based on the meaning that the girl had assigned to a bee through her previous knowledge and experiences. That meaning is what prompted the behavioral response to flee.

Vision

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Your eyes are made up of different interworking parts. Light enters through the cornea, which is located at the front of the eye (Griggs, 2016). The cornea begins the process as it starts to bend the light waves that then passes through to the pupil. The pupil is a tiny hole that lets light through. It is controlled by the iris, which gives the eye its color and regulates the size of the pupil (Griggs, 2016). The iris adjusts the amount of light that enters the eye, then the light moves through a transparent lens, which adjusts the focus of the images (Griggs, 2016). The lens is flexible and can change in shape to take in either distant or close images. This ability to change in shape to fit the distance of images is called accommodation (Griggs, 2016). The cornea and lens together determine the eye’s focusing power. About two-thirds of light is reflected by the cornea, while the remaining third passes to the lens. The lens can change its shape in order to focus the light from objects at different distances, while the cornea remains fixed in place (Goldstein & Brockmole, 2017).

Neurons

· MESSAGE TRANSPORTERS

· PARTS OF A NEURON

· SPECIALIZATION OF NEURONS

· HOW A MESSAGE TRAVELS

Neurons consist of different parts responsible for electrically transmitting the message through each neuron:

· The dendrites are the branchlike structures that first receive information.

· The soma, or cell body, maintains the health and metabolism of the cell.

· The nucleus resides within the soma, and is responsible for making the proteins that maintain cell function. The nucleus also houses the DNA for the cell.

· The axon is the long nerve fiber that is connected to the soma, and transmits the information that is passed on from the soma.

· The terminal branch is at the end of each neuron. It is the launching place of the information from that neuron across the synapse to the next neuron.

· The synapse is the very small gap between each neuron.

· Reception and Transduction

Vision

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Neurons

· MESSAGE TRANSPORTERS

· PARTS OF A NEURON

· SPECIALIZATION OF NEURONS

· HOW A MESSAGE TRAVELS

Neurons consist of different parts responsible for electrically transmitting the message through each neuron:

· The dendrites are the branchlike structures that first receive information.

· The soma, or cell body, maintains the health and metabolism of the cell.

· The nucleus resides within the soma, and is responsible for making the proteins that maintain cell function. The nucleus also houses the DNA for the cell.

· The axon is the long nerve fiber that is connected to the soma, and transmits the information that is passed on from the soma.

· The terminal branch is at the end of each neuron. It is the launching place of the information from that neuron across the synapse to the next neuron.

· The synapse is the very small gap between each neuron.

Now that we have some background on the neuron as a single functioning unit and how signals travel through individually, it is time to look at neurons collectively as they work in the retina. Five different types of neurons are layered together into interconnected neural circuits within the retina. As we discussed earlier, information travels from receptor cells to bipolar cells to ganglion cells. There are two other types of neurons that are part of the connections in the retina: the horizontal cells that send signals between receptor neurons, and amacrine cells that pass signals between the bipolar and ganglion cells. Neural convergence, or convergence occurs when multiple neurons synapse onto one neuron. In the retina, there are 126 million receptor cells and 1 million ganglion cells, which means multiple receptor cells will send signals to the same ganglion cell. There are 120 million rods and 6 million cones in the retina, so again, there is a difference in the number of cells sending information to the ganglion cells. Based on these numbers, we can see that more rods will send signals to ganglion cells than cones. The greater convergence of rods results in more sensitivity than cones, and better detail vision in cones than rods (Goldstein & Brockmole, 2017).

As we have just seen, rods are more sensitive than cones. In the daylight, the intensity of light is much greater than at night, so there are many photons hitting the retina. At night or in dim light, the intensity of light is low, meaning far fewer photons reach the retina. This is why we need lots more rods than cones. When you are walking in dim light, you are using your rods to detect the objects you are looking at. So, less light is needed by the rods to identify the stimuli in your presence. Cones have better visual acuity, or ability to distinguish details (Goldstein & Brockmole, 2017). This visual acuity would have been beneficial to the girl as she looked for a small bee in a large field of flowers.

Conclusion

Let’s revisit the girl and her bee. We have just learned how much goes into hearing buzzing, looking for the sound, seeing a bee, recognizing the bee and remembering what a bee does and moving away from the bee. Try an experiment: listen for a sound, turn toward the sound, identify it and then wave your hand. How long did it take you? Did it seem like any time passed at all? Yet, quite a bit occurred in that seemingly infinitesimal period of time. The sound was transmitted through the auditory system via neural networks, transduced, processed by the brain. A message was then sent from the brain through motor neurons to have the head move to find the source of the sound. The visual systems picked up the light reflection of the bee, sent it through the optical systems, transduced it and moved it to the brains systems for processing. The brain then sent the message to motor neurons to move. Thousands of neurons were activated to send these messages. All of this happened in a period of time we would experience as instant.

In our next lesson we will look at the trip the message takes through the nervous system in more detail.

Sources

Carlson, N. R., Miller, H. L., Heth, D. S., Donahoe, J. W., & Martin, G. N. (2010). Psychology: The science of behavior (7th ed.). Boston, MA: Allyn & Bacon.

Goldstein, E. B. & Brockmole, J. R. (2017). Sensation and perception (10th ed.). Boston, MA: Cengage.

Griggs, R. A. (2016). Psychology: A concise introduction (5th ed.). New York, NY: Worth Publishers.

Image Citations

"A bee on a flower " by https://pixabay.com/en/bee-lavender-insect-nature-yellow-1040521/.

"A hearing test: a girl has on headphones and her eyes closed as a technician changes which ear receives the sound" by 36420083.

"Visible spectrum of light" by 20609699.

"Close up of an eye " by https://pixabay.com/en/eye-iris-algae-macro-blur-natural-2340806/.

"Alt text: Anatomy of the eye, as described in this section of the lesson, with a ray of light being focused on the fovea" by https://commons.wikimedia.org/wiki/File:Cataracts.png.

"Anatomy of the ear, as described in this section of the lesson" by 59184884

"Anatomy of a neuron, as described in this section of the lesson" by 56921155

"A diagram that shows messages traveling across the synapse between two nerves" by https://en.wikipedia.org/wiki/Synapse#/media/File:Chemical_synapse_schema_cropped.jpg.

"Anatomy of the ear, as described in this section of the lesson" by https://pixabay.com/en/eye-diagram-eyeball-body-pupil-39998/.

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WEEK 2

https://youtu.be/bk0raUXwCjc

READING

Introduction

Topics to be covered include:

The components of sound and how they interact
The function of the cochlea
Localization of sound

In this lesson, we will learn more about sound and the auditory systems that sound waves pass through as they are transmuted to signals the brain can understand. Sound travels as vibrations through the outer and middle ears before it is transmuted to electrical signals in the inner ear. We will also look at how we are able to identify where a sound came from, and how sound hits each of our ears.

How We Rely on Sound

For many, sight is the first sense we rely on. We see something and go by what we see. Yet, we cannot always see something, and what we perceive based on our sight is not always accurate. So, which sense do we rely on more than we realize? We can hear in the dark, and while we can be fooled by sounds, we might be a little more cautious with what we hear as opposed to what we see. We use our hearing to listen to and identify different sounds. Some sounds are enjoyable, and others might be a little too loud, or have an unpleasant sound, like a siren or a child playing the same note on a recorder for the fiftieth time trying to get it just right.

Yet, let’s look at an example that will help us explain sound and auditory perception. We are at a concert for second grade children playing their recorders, the plastic flute-like instruments elementary children often learn to play notes on. A couple of children seem to be doing better than others, and have solo parts. Parents scramble to record their children and happily move to the sounds that fill the auditorium. Of course, some visitors might not conclude that the recorders are quite as melodious as they listen to the concert. In each case, pressure changes in the air create the stimulus for hearing, similar to how light is processed by visual senses. This change in air pressure activates the auditory senses. The information travels through the outer ear to the middle ear, then to the inner ear. The information is processed and sent through brains systems to create a perceptual experience. We have systems that help us determine where the sound comes from, based on how quickly it hits an ear, and which ear it hits first. In some ways, this information is more reliable than visual senses.

Physical and Perceptual Definitions of Sound

This video shows how sounds are produced and how you hear them: What is Sound?

Open file: Transcript ‹1/5 ›

The StimulusLike vision, sound begins with a distal stimulus. In our example, the distal stimulus would be the sound of the recorder. The vibration of the recorder causes changes in the air that trigger auditory organs to process this representation of sound and send it to the brain. This sound is physically based on the pressure changes that occur as the sound is emitted from the distal stimulus (Goldstein & Brockmole, 2017). The sound is also perceptually based on our experience– we perceive the recorder sound as wonderful (if you are mom), or as perhaps a little annoying (if you are anyone other than mom). So, we have the recorder vibrating with a frequency of 1,000 Hertz (Hz), which is the physical stimulus, and the experience of sound based on your enjoyment of the recorder concert (Goldstein & Brockmole, 2017).

Loudness and Pitch

The frequency of sound is on the horizontal axis; the dB levels at which we can hear each frequency is on the vertical axis.

LOUDNESS
PITCH
TIMBRE

The amplitude of a sound is expressed in dB. The perceptual aspect of the sound stimulus loudness is related to the level of an auditory stimulus. The higher the dB the louder we perceive a sound, but this varies with the frequency of the sound. The audibility curve indicates the range of frequencies we can hear. Underneath the audibility curve we would not be able to hear talk, but above the curve we can hear tones. This area above the curve is called the auditory response area. The area above the upper range of the audibility curve is the threshold of feeling, which is an area where the amplitudes are so high that we can feel them, and they would likely cause us pain, but we wouldn’t necessarily hear them (Goldstein & Brockmole, 2017). How many of you have ever heard of a dog whistle? The amplitude of a dog whistle is so high that we, as humans, cannot hear it but dogs can. Dogs can hear frequencies higher in the human audibility curve. As you get older, the range of frequencies you can hear shrinks. You can test your hearing at: Hearing Test. (transcript not yet available)

The video plays sounds of the frequency indicated on the screen. Watch the video until you can hear the sound. That is the lower threshold of your hearing. Towards the end of the video you will probably find that you cannot hear sounds above a certain frequency.

The Journey through the Ear

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THE OUTER EAR Now that we have seen sound travel from the distal stimulus to the ear, it is time to see happens once it reaches the ear. We took an abbreviated journey through the ear in Lesson 1 and now we will look at this journey in more detail. The journey begins with the outer ear. The structure of the outer ear that we all see is called the pinna (plural pinnae). From the pinnae sound travels through the auditory canal, which is the tube-like recess that leads to the eardrum, also called the tympanic membrane. When you find wax in your ear, you find it in the auditory canal. The purpose of the wax and the small size of the canal is to protect the eardrum. The auditory canal also enhances the intensity of sound through resonance. Resonance is a result of the interaction between soundwaves reflected back from the close end of the auditory canal with new soundwaves entering the canal (Goldstein & Brockmole, 2017).

Vibrations and Electrical Signals

FROM SOUND TO ELECTRICAL SIGNALS TO BRAIN
PLACE THEORY
FREQUENCY TUNING CURVE
COCHLEAR AMPLIFIER

As sound vibrations move through the stapes and press against the oval window, the oval window begins a back-and-forth motion that transmit the vibrations to the liquid inside the cochlea, which, in turn, sets the basilar membrane into an up and down motion. Remember that the basilar membrane lies below the organ of Corti, so the up and down motions cause the organ of Corti to move up and down also. The organ of Corti in turn causes the tectorial membrane to move back and forth just above the outer hair cells. At this point, the vibrations are transformed into electrical signals, beginning the process of transduction. As the cilia of the hair cells bend in one direction structures called tip links are stretched, opening tiny ion channels in cilia membranes. When its channels are open, positive ions flow into the cell and create an electric signal. When the cilia bend in the opposite direction, the tip links go slack, ion channels close and the electrical signal stops. This causes alternating bursts of electrical signals and no electrical signals as the tip links stretch and then slacken. When signals are sent, neurotransmitters are released to cross the synapse between the inner hair cells and the auditory nerve fibers, which causes the nerve fibers to fire. If you think about this, you see a pattern. The auditory nerve fibers fire with the rising and falling pressure of a pattern from a pure tone. When the auditory nerve fibers fire at the same place in the sound stimulus is called phase locking (Goldstein & Brockmole, 2017).

Frequency Theory

Remember that pitch is concerned with the quality of the sound described as high or low. This is determined based on the frequency, which we have just seen is impacted by place. So, what is pitch impacted by? One other theory is frequency theory, which proposes that the frequency of the sound wave throughout the basilar membrane is the same as the firing rate of the hair cells. If, for example, a frequency of the sound is 300 Hz, the firing rate of the hair cells across the basilar membrane would be 300 pulses per second. So, if we put the place theory and the frequency theory together, what would we get? Research has determined that specific locations on the basilar membrane match specific sound wave frequencies – except for the lower ones. The lower ones seem to match the frequency theory and the firing rate of the entire basilar membrane. There is a maximum firing rate for nerve cells, and cells take turns firing, which increases the maximum firing rate for all of the cells in the group. This process is called the volley principle, and between place theory, frequency theory, and the volley principle, we can see how information is processed by the brain to perceive pitch (Griggs, 2016).

From the Cochlea to the Brain

Now that we have seen what happens in the cochlea, let’s move out of the cochlea and continue toward the brain. The auditory nerve carries the signal away from the cochlea toward a sequence of subcortical structures. The first structure is the cochlear nucleus, and then the superior olivary nucleus in the brain stem. This signal then moves to the inferior colliculus located in the midbrain, and then on to the medial geniculate nucleus in the thalamus. The signal continues from the thalamus to the primary auditory cortex in the temporal lobe. While the exact location of the brain specifically responsible for response to pitch, the most responsive area seems to be the anterior auditory cortex, which is an area close to the front of the brain (Goldstein & Brockmole, 2017).

Hearing Loss

This graph demonstrates the hearing damage for workers in a noisy weaving factory. dBA is another abbreviation of dB.

So far, we have looked at the process for normal hearing. What if someone experiences a loss of hearing? How does that happen? Most hearing loss is associated with the outer hair cells, and damage to auditory nerve fibers. Damage to outer hair cells results in a loss of sensitivity in the basilar membrane, making it harder for someone to separate sounds, such as hearing a door close during a concert. Inner hair cell damage can also result in loss of sensitivity.

One form of hair loss is presbycusis, which is caused by damage to hair cells from extended exposure to loud noise, ingestion of substances that can cause hair cell damage, and age-related degeneration. There is a loss of sensitivity that is more pronounced at higher frequencies with presbycusis, and tends to have a higher prevalence in males than females. Noise-induced hearing loss is another form of hearing degeneration resulting from loud noises. In this case, the damage often involves the organ of Corti. It is also possible to have hearing loss that is not indicated by standard hearing test results, called hidden hearing loss. Standard hearing tests often measure hair cell function, which might not indicate issues with complex sounds (Goldstein & Brockmole, 2017).

Perception of Sound

We have covered perception of sound based on pitch, frequency and amplitude, so now what about how we perceive where a sound comes from? Imagine you are at the concert and you hear a baby crying in the audience. You turn your head to the left and see the parent quickly ferrying the child out of the auditorium. You knew where to look based on auditory localization. Now, let’s say you are in the school’s waiting room, waiting with other parents for your child’s name to be called so you can pick them up. It is a small room with quite a few parents, and when the teacher calls your name, you are able to hear it the first time, even though it travels two different paths – directly from the teacher’s mouth to your ears, and by bouncing off the walls of the small room. The fact that your auditory perception relies mainly on the direct path is called precedence effect. Think about this small, noisy waiting room again. Many parents are talking to each other. You are speaking with two parents, and are able to hear what they are saying even though others are talking all around you. Your ability to segregate your conversation from the other conversations in the area is called auditory stream segregation (Goldstein & Brockmole, 2017).

Localization of Sound

Let’s think back to our first scenario where we heard the baby crying while the concert recorder band is playing. You hear sounds from two different directions, which creates an auditory space When you locate the sound of the baby in that auditory space, it is called auditory localization. If you think about the baby’s cry and the sound of the recorders, you will see that they are different and would stimulate different hair cells and nerve fibers in the cochlea. Thus, the auditory system uses location cues created by the way the sound interacts with your head and ears. The two location cues are binaural cues, which depend on information from both ears, and monaural cues, which depends on information from just one ear. Research indicates three dimensions are involved in location of sound: the azimuth, extending from left to right, the elevation, extending up and down, and the distance the sound travels from its source to the person listening to it.

Binaural cues use the time it takes to reach both ears to determine horizontal positions (left or right), but they do not help with vertical information (azimuth). There are two types of binaural cues, interaural level difference, which is based on the difference in sound level, and interaural time difference, which is based on the difference between the time it takes for a sound to reach the left ear, and the time it takes for a sound to reach the right ear. Both time and level differences can be the same at different elevations, which means they do not account for the elevation of a sound, causing a place of ambiguity, or cone of confusion. Information using monaural cues can locate sounds at different elevations using the spectral cue (Goldstein & Brockmole, 2017).

NEURAL SIGNALS

Now that we have identified different cues, think about how they might send and receive signals through neural circuits. One theory, the Jeffress model, proposes that neurons used to transmit signals from the ears are designed to receive signals from both ears. In other words, each neuron processes signals from both ears. The signals move inward and ultimate meet as the neurons sending the sound from the right ear meet the neurons sending the sound from the left ear. The neuron they meet at are called coincidence detectors because they only fire when both signals meet at the same time. When they meet at the same time at this neuron, the neuron indicates that interaural time difference is zero. If the sound comes from one side first, the signal from the ear on that side begins sending signals before the other ear (Goldstein & Brockmole, 2017).

Auditory Areas of the Brain

Areas of the brain that have been indicated in sound location include the back of the cortex, or posterior belt area, and an area toward the front of the cortex, or the anterior belt area. There seems to be a “what” auditory pathway that extends from the anterior belt to the frontal cortex, and the “where” auditory pathway, which extend from the posterior belt to the frontal cortex. The “what” pathway works with determining what a sound is, and the “where” pathway determines where the sound is coming from (Goldstein & Brockmole, 2017).

BACK TO THE WAITING ROOM

We are going to return to the recorder concert. If the concert had been outside, perception of the sounds would have directly moved from the recorders to your ears, or direct sound. This concert was inside in an auditorium, so sound reached the ears of the parents through the direct path, and by bouncing off of the various surfaces of the auditorium, which is indirect sound. As parents talk to each other in separate groups, adding to a general array of sound sources the environment is called the auditory scene. You are able to separate out and listen to your conversation with another parent even though numerous conversations were going on around you. This ability to separate the sound from each source is called auditory scene analysis.

Imagine that you hear your name from a female voice while you are talking to a parent, and you saw someone open their mouth and look your way at the same time, so you believed the sound of your name came from that person (even though another parent said your name). You did this based on the ventriloquist effect, which occurs when sounds come from one place, but appear to come from another. In this case, you relied more on your vision than your hearing, and you were wrong. On the other side of this, people can use echolocation to detect the positions and shapes of objects without sight. People who cannot see often learn this technique of making a clicking sound and listening for echoes to determine locations and shapes (Goldstein & Brockmole, 2017). These examples show how important hearing is as a source of sensory information.

Conclusion

A simple concert shows us how much we use our hearing in our daily lives. Sound is processed as vibrations that are transported through the outer ear to the middle and then inner ear systems. Systems in the inner ear are responsible for transforming the vibrations into electrical signals that the brain can understand as audio messages. We also have mechanisms that help us determine where a sound is coming from based on which ear the sound arrives at first. Of course, sometimes we can be mistaken. This can happen when our eyes register one thing while our ears register a sound, causing us to make an assumption about where the sound comes from. Sound is important, and our ears can provide information when our eyes cannot, or when our eyes are mistaken.

Sources

Goldstein, E. B. & Brockmole, J. R. (2017). Sensation and perception (10th ed.). Boston, MA: Cengage.

Griggs, R. A. (2016). Psychology: A concise introduction (5th ed.). New York, NY: Worth Publishers.

Image Citations

"A close up of a microphone " by https://pixabay.com/en/microphone-shure-singing-music-2498641/.

"A graph representing sound, with time on the x-axis and air pressure on the y-axis" by http://oceanexplorer.noaa.gov/explorations/sound01/background/acoustics/media/sinewave_261.jpg.

"An audibility graph showing the dB level needed to hear sounds of different frequencies" by https://upload.wikimedia.org/wikipedia/commons/b/bc/Audible.JPG.

"The anatomy of the ear as described in this section." by 13699578_ML.

"The middle ear anatomy" by 13699578_ML.

"The anatomy of the cochlea " by 46938501.

"The organ of Corti" by 73652691.

"The auditory pathway" by 15313015.

"A graph showing the hearing loss of workers in a noisy weaving factory" by https://commons.wikimedia.org/w/index.php?search=threshold of hearing&title=Special:Search&profile=default&fulltext=1&searchToken=975xk3qgfyy96u9ixxtnhepzs#/media/File:Permanent_threshold_shift_(hearing_loss)_after_no

WEEK 3

https://www.youtube.com/watch?v=o0DYP-u1rNM

https://www.youtube.com/watch?v=6YxffFmi4Eo

https://www.youtube.com/embed/1ss2EWgRCM4?wmode=opaque&rel=0

https://www.youtube.com/embed/Rxl_jh4N_iQ?wmode=opaque&rel=0

https://www.intechopen.com/books/advances-in-ophthalmology/astigmatism

http://www.innerbody.com/image/nervov.html

https://www.intechopen.com/books/advances-in-ophthalmology/myopia-light-and-circadian-rhythms

Nervous System

By: Tim Barclay, PhD

Medically reviewed by: Stephanie Curreli, MD, PhD

Last Updated: Apr 9, 2020

The nervous system consists of the brain, spinal cord, sensory organs, and all of the nerves that connect these organs with the rest of the body. Together, these organs are responsible for the control of the body and communication among its parts. The brain and spinal cord form the control center known as the central nervous system (CNS), where information is evaluated and decisions made. The sensory nerves and sense organs of the peripheral nervous system (PNS) monitor conditions inside and outside of the body and send this information to the CNS. Efferent nerves in the PNS carry signals from the control center to the muscles, glands, and organs to regulate their functions. CONTINUE SCROLLING TO READ MORE BELOW...

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Nervous System Anatomy

Nervous Tissue

The majority of the nervous system is tissue made up of two classes of cells: neurons and neuroglia.

Neurons

Neurons, also known as nerve cells, communicate within the body by transmitting electrochemical signals. Neurons look quite different from other cells in the body due to the many long cellular processes that extend from their central cell body. The cell body is the roughly round part of a neuron that contains the nucleus, mitochondria, and most of the cellular organelles. Small tree-like structures called dendrites extend from the cell body to pick up stimuli from the environment, other neurons, or sensory receptor cells. Long transmitting processes called axons extend from the cell body to send signals onward to other neurons or effector cells in the body.

There are 3 basic classes of neurons: afferent neurons, efferent neurons, and interneurons.

1. Afferent neurons. Also known as sensory neurons, afferent neurons transmit sensory signals to the central nervous system from receptors in the body.

2. Efferent neurons. Also known as motor neurons, efferent neurons transmit signals from the central nervous system to effectors in the body such as muscles and glands.

3. Interneurons. Interneurons form complex networks within the central nervous system to integrate the information received from afferent neurons and to direct the function of the body through efferent neurons.

Neuroglia

Neuroglia, also known as glial cells, act as the “helper” cells of the nervous system. Each neuron in the body is surrounded by anywhere from 6 to 60 neuroglia that protect, feed, and insulate the neuron. Because neurons are extremely specialized cells that are essential to body function and almost never reproduce, neuroglia are vital to maintaining a functional nervous system.

Brain

The brain, a soft, wrinkled organ that weighs about 3 pounds, is located inside the cranial cavity, where the bones of the skull surround and protect it. The approximately 100 billion neurons of the brain form the main control center of the body. The brain and spinal cord together form the central nervous system (CNS), where information is processed and responses originate. The brain, the seat of higher mental functions such as consciousness, memory, planning, and voluntary actions, also controls lower body functions such as the maintenance of respiration, heart rate, blood pressure, and digestion.

Spinal Cord

The spinal cord is a long, thin mass of bundled neurons that carries information through the vertebral cavity of the spine beginning at the medulla oblongata of the brain on its superior end and continuing inferiorly to the lumbar region of the spine. In the lumbar region, the spinal cord separates into a bundle of individual nerves called the cauda equina (due to its resemblance to a horse’s tail) that continues inferiorly to the sacrum and coccyx. The white matter of the spinal cord functions as the main conduit of nerve signals to the body from the brain. The grey matter of the spinal cord integrates reflexes to stimuli.

Nerves

Nerves are bundles of axons in the peripheral nervous system (PNS) that act as information highways to carry signals between the brain and spinal cord and the rest of the body. Each axon is wrapped in a connective tissue sheath called the endoneurium. Individual axons of the nerve are bundled into groups of axons called fascicles, wrapped in a sheath of connective tissue called the perineurium. Finally, many fascicles are wrapped together in another layer of connective tissue called the epineurium to form a whole nerve. The wrapping of nerves with connective tissue helps to protect the axons and to increase the speed of their communication within the body.

· Afferent, Efferent, and Mixed Nerves. Some of the nerves in the body are specialized for carrying information in only one direction, similar to a one-way street. Nerves that carry information from sensory receptors to the central nervous system only are called afferent nerves. Other neurons, known as efferent nerves, carry signals only from the central nervous system to effectors such as muscles and glands. Finally, some nerves are mixed nerves that contain both afferent and efferent axons. Mixed nerves function like 2-way streets where afferent axons act as lanes heading toward the central nervous system and efferent axons act as lanes heading away from the central nervous system.

· Cranial Nerves. Extending from the inferior side of the brain are 12 pairs of cranial nerves. Each cranial nerve pair is identified by a Roman numeral 1 to 12 based upon its location along the anterior-posterior axis of the brain. Each nerve also has a descriptive name (e.g. olfactory, optic, etc.) that identifies its function or location. The cranial nerves provide a direct connection to the brain for the special sense organs, muscles of the head, neck, and shoulders, the heart, and the GI tract.

· Spinal Nerves. Extending from the left and right sides of the spinal cord are 31 pairs of spinal nerves. The spinal nerves are mixed nerves that carry both sensory and motor signals between the spinal cord and specific regions of the body. The 31 spinal nerves are split into 5 groups named for the 5 regions of the vertebral column. Thus, there are 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves, and 1 pair of coccygeal nerves. Each spinal nerve exits from the spinal cord through the intervertebral foramen between a pair of vertebrae or between the C1 vertebra and the occipital bone of the skull.

Meninges

The meninges are the protective coverings of the central nervous system (CNS). They consist of three layers: the dura mater, arachnoid mater, and pia mater.

· Dura mater. The dura mater, which means “tough mother,” is the thickest, toughest, and most superficial layer of meninges. Made of dense irregular connective tissue, it contains many tough collagen fibers and blood vessels. Dura mater protects the CNS from external damage, contains the cerebrospinal fluid that surrounds the CNS, and provides blood to the nervous tissue of the CNS.

· Arachnoid mater. The arachnoid mater, which means “spider-like mother,” is much thinner and more delicate than the dura mater. It lines the inside of the dura mater and contains many thin fibers that connect it to the underlying pia mater. These fibers cross a fluid-filled space called the subarachnoid space between the arachnoid mater and the pia mater.

· Pia mater. The pia mater, which means “tender mother,” is a thin and delicate layer of tissue that rests on the outside of the brain and spinal cord. Containing many blood vessels that feed the nervous tissue of the CNS, the pia mater penetrates into the valleys of the sulci and fissures of the brain as it covers the entire surface of the CNS.

Cerebrospinal Fluid

The space surrounding the organs of the CNS is filled with a clear fluid known as cerebrospinal fluid (CSF). CSF is formed from blood plasma by special structures called choroid plexuses. The choroid plexuses contain many capillaries lined with epithelial tissue that filters blood plasma and allows the filtered fluid to enter the space around the brain.

Newly created CSF flows through the inside of the brain in hollow spaces called ventricles and through a small cavity in the middle of the spinal cord called the central canal. CSF also flows through the subarachnoid space around the outside of the brain and spinal cord. CSF is constantly produced at the choroid plexuses and is reabsorbed into the bloodstream at structures called arachnoid villi.

Cerebrospinal fluid provides several vital functions to the central nervous system:

1. CSF absorbs shocks between the brain and skull and between the spinal cord and vertebrae. This shock absorption protects the CNS from blows or sudden changes in velocity, such as during a car accident.

2. The brain and spinal cord float within the CSF, reducing their apparent weight through buoyancy. The brain is a very large but soft organ that requires a high volume of blood to function effectively. The reduced weight in cerebrospinal fluid allows the blood vessels of the brain to remain open and helps protect the nervous tissue from becoming crushed under its own weight.

3. CSF helps to maintain chemical homeostasis within the central nervous system. It contains ions, nutrients, oxygen, and albumins that support the chemical and osmotic balance of nervous tissue. CSF also removes waste products that form as byproducts of cellular metabolism within nervous tissue.

Sense Organs

All of the bodies’ many sense organs are components of the nervous system. What are known as the special senses—vision, taste, smell, hearing, and balance—are all detected by specialized organs such as the eyes, taste buds, and olfactory epithelium. Sensory receptors for the general senses like touch, temperature, and pain are found throughout most of the body. All of the sensory receptors of the body are connected to afferent neurons that carry their sensory information to the CNS to be processed and integrated.

Nervous System Physiology

Functions of the Nervous System

The nervous system has 3 main functions: sensory, integration, and motor.

1. Sensory. The sensory function of the nervous system involves collecting information from sensory receptors that monitor the body’s internal and external conditions. These signals are then passed on to the central nervous system (CNS) for further processing by afferent neurons (and nerves).

2. Integration. The process of integration is the processing of the many sensory signals that are passed into the CNS at any given time. These signals are evaluated, compared, used for decision making, discarded or committed to memory as deemed appropriate. Integration takes place in the gray matter of the brain and spinal cord and is performed by interneurons. Many interneurons work together to form complex networks that provide this processing power.

3. Motor. Once the networks of interneurons in the CNS evaluate sensory information and decide on an action, they stimulate efferent neurons. Efferent neurons (also called motor neurons) carry signals from the gray matter of the CNS through the nerves of the peripheral nervous system to effector cells. The effector may be smooth, cardiac, or skeletal muscle tissue or glandular tissue. The effector then releases a hormone or moves a part of the body to respond to the stimulus.

Unfortunately of course, our nervous system doesn’t always function as it should. Sometimes this is the result of diseases like Alzheimer’s and Parkinson’s disease. Did you know that DNA testing can help you discover your genetic risk of acquiring certain health conditions that affect the organs of our nervous system? Late-onset Alzheimer’s, Parkinson’s disease, macular degeneration - visit our guide to DNA health testing to find out more.

Divisions of the Nervous System

Central Nervous System

The brain and spinal cord together form the central nervous system, or CNS. The CNS acts as the control center of the body by providing its processing, memory, and regulation systems. The CNS takes in all of the conscious and subconscious sensory information from the body’s sensory receptors to stay aware of the body’s internal and external conditions. Using this sensory information, it makes decisions about both conscious and subconscious actions to take to maintain the body’s homeostasis and ensure its survival. The CNS is also responsible for the higher function