. Processes in perception.

ASSIGNMENT 300 WORDS MINIMUM

After watching the two videos below, discuss the role of higher-level or “cognitive” processes in perception. Then describe a situation in which you initially thought you saw or heard something, but then realized that your initial perception was in error. What was the role of bottom-up and top-down processing in this process of first having an incorrect perception and then realizing what was actually there?

Support your belief and use specific examples. You may refer to your assigned Week 1 readings or draw on scholarly online resources. The latter must be academic in nature (e.g. from the APUS online library) and not from pop culture and/or commercial websites, blogs, opinion sites, etc.

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

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.

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/.