Exploring Human Senses AP Psych Lab Stations

KEY QUESTION: How do structures in the body enable human beings to sense their environment? BACKGROUND: In the human body, specialized nerve cells respond to conditions in the environment and send a signal through other nerve cells to the brain. These specialized nerve cells have structures called sensory receptors, structures that will only respond to a specific kind of stimulus. There are many types of receptors in the human body. Working together, these receptors send signals to the brain that enable our senses of sight, hearing, taste, touch, and smell. The figure below summarizes the five senses and the types of sensory receptors involved.

PROCEDURE

1. Station 17 will be completed as a large group before you start rotating stations. 2. Working in groups of 3 or 4, rotate through each station. 3. Read and HIGHLIGHT the Background Information (when provided) before completing the activity. 4. Read the procedures, perform the activity, and record your information in the sections that correspond

to each station. 5. Rotate roles in your group so that each person can be the.subject, the observer, and the recorder for

each station.

Station 1: Light and Deep Touch 

Background The skin is the largest sensory organ of the body. The skin has many sensory receptors for cutaneous sensations and is sensitive to many kinds of stimuli including touch, pressure, temperature, and pain. Sensory receptors are structures on sensory neurons that respond to a specific stimulus like touch. Cutaneous sensations are sensations that come from the skin. The acuteness of a sensation depends on the density of the receptors and the size of the receptive field in the area that is being stimulated. Receptor density is equal to the number of receptors per unit area, and this varies by location across the body surface. A receptive field is the area on the skin that activates a sensory neuron. Receptive fields may be small and numerous or large and overlapping. Areas of the body such as the tongue, lips, back of the neck, and fingertips possess higher receptor densities with smaller receptive fields and can therefore sense stimuli more acutely. Areas such as the back, arms, palms, thighs, and calves have fewer receptors per unit area and larger receptive fields. These areas have lower sensitivity and discrimination ability. During this activity, you will measure the skin's sensitivity to touch and pressure. Meissner's corpuscles are nerve endings in the skin that are responsible for detecting the sensation of light touch. They are most prevalent in the fingertips and on the tongue. Other parts of the body are less sensitive to light touch. Pacinian corpuscles are nerve fibers surrounded by thin coverings of connective tissue; they respond to pressure on the skin. Data Results

Compare the results for the three areas. Is the number of positive responses to a light touch the same in all three areas? Why or why not?

Compare the results for the three areas. Are there differences in pressure sensitivity? Why or why not?

Station 2: Thermoreception 

Background The skin is the largest sensory organ of the body. The skin has many receptor sites for cutaneous sensations and is sensitive to many kinds of stimuli including touch, pressure, temperature, and pain. The acuteness of a sensation depends on the density of the cutaneous receptors and the size of the receptive field in the area that is being stimulated. Receptor density is equal to the number of receptors per unit area, and this varies by location across the body surface. A receptive field is the area on the skin that activates a sensory neuron. Receptive fields may be small and numerous or large and overlapping. Areas of the body such as the tongue, lips, back of the neck, and fingertips possess higher receptor densities with smaller receptive fields and can therefore sense stimuli more acutely. Areas such as the back, arms, palms, thighs, and calves have fewer receptors per unit area and larger receptive fields. These areas have lower sensitivity and discrimination ability. During this activity, you will measure the skin's sensitivity to temperature. The corpuscles of Krause and Ruffini are sense organs that provide information in response to cold and hot, respectively.

Data Results

Examine your data. Did you identify more warm or cold receptor sites?

Were any areas sensitive to both heat and cold? If so, which?

Why is sensitivity to both heat and cold important?

Station 3: Two-Point Discrimination 

Background The integration of responses from cutaneous receptors by the brain and spinal cord results in perception of the type of sensation and the location of the sensation. The distribution of receptors is not uniform. Thus, despite stimulation of separate nerves 5 to 6 centimeters apart, two distinct, simultaneous touches on the back are often perceived as one touch by the central nervous system. Two simultaneous touches are distinguished only if there are two stimulated receptors. The tongue, however, can distinguish touches as close as 1 millimeter apart, and interpretation of information from fingertips allows awareness of two distinct touches 2.5 millimeters apart. Data Results

Are some locations more sensitive than others? Based on the two-point discrimination data for these four areas of the skin, what inferences can you make regarding receptor densities in these areas?

   

Station 4: Taste 

Background Humans can detect five distinctive taste qualities: bitter, salty, sour, sweet, and umami (a savory taste of amino acids). "Umami" is the Japanese word for delicious. Taste receptor cells (TRCs) respond to chemicals dissolved in saliva. The different TRCs respond to different substances. Although each type of taste receptor is most responsive to a particular substance, every type can be stimulated by a broad range of chemicals, resulting in the complexity of our sense of taste. How do we know if something is bitter? The act of tasting something bitter can be summarized as a two-step process. First, a molecule binds to a specific receptor protein on the tongue. The binding of the molecule to the receptor then generates a signal that is sent from the cell to the brain, allowing you to perceive a bitter taste sensation. The receptors in your taste buds are so specific that they can detect even slight differences between molecules. The binding strength between a taste molecule and a receptor is determined by the shape of the receptor, and a tightly bound molecule produces a strong taste sensation. The shape of the receptor is influenced by genetic factors. For this station, you will test for your ability to taste some substances that have been embedded in paper strips.

● Control Taste Paper: This untreated paper is a control. Any taste sensation that you have from this paper is a result of the paper, and not the result of any chemical additive.

● PTC Taste Paper: Phenylthiocarbamide (PTC) is a type of thiourea. Tasters perceive PTC as bitter. The ability to taste PTC is controlled by the "PTC gene;' TAS2R38.

● Thiourea Taste Paper: Thiourea is the name for a molecule with -N-C=S within its structure. Many chemicals with this structure will bind to the bitter taste receptor regulated by the TAS2R38 alleles. Tasters perceive thiourea as bitter.

● Sodium Benzoate Taste Paper: It is not fully understood how the ability to taste sodium benzoate is regulated. The most common taste perceptions of sodium benzoate are sweet, salty, bitter, and tasteless.

Data Results

Why can some people aste the PTC, sodium benzoate, and thiourea taste papers, while others cannot?

Station 5: Smell (Olfactory Fatigue and Memory) 

SAFETY!!! The test subject should wear the protective eyewear during this activity.

Background Unlike taste sensations (of which there are only five), there are numerous smell responses, stimulated by many types of chemicals. This results in a great number and variety of odors. The organs of human smell, the olfactory epithelium, are in the upper portion of each nasal cavity. This region consists of olfactory receptor cells found in tiny, hairlike cilia that are bathed in a layer of mucus. Gaseous odor molecules dissolve in this mucus layer and bind to the membranes of the receptor cells. Axons from the receptor cells carry impulses to the olfactory bulb, which lies under the frontal lobe of the brain. In time, sensitivity to continuous odors may diminish or even become nonexistent, while the response to other odors is unimpaired. This phenomenon is known as "olfactory fatigue:' In this exercise, you will explore how long you retain the ability to smell an odor before the scent begins to fade or becomes imperceptible. Data Results

Fragrance Right Nostril Fatigue Left Nostril Fatigue

Clove Oil

Peppermint Oil

How much time elapsed before you culd no longer smell the clove oil, or the smell greatly diminished?

Could you smell the peppermint oil immediately after the diminished odor of the clove oil? What does this say about the nose’s ability to detect new or different odors?

How do the fatigue times of the clove oil and the peppermint oil compare when sniffed in succession with the right nostril?

Did switching to the left nostril to sniff the clove oil and peppermint oil diminish or enhance the odors?

Is the fatigue time for the left nostril significantly different that the right nostril? Why or why not?

When you smelled the cloves and the peppermint, describe any memories that you associated with those odors.

Station 6: Blind Spot 

Background The retina of the eye possesses two types of specialized, light-detecting nerve cells known as photoreceptors. They are called rods and cones because of their distinctive shapes. Rods function in dim light and perceive shades of gray, like what you see when your eyes adjust to darkness. There are about 120 million rods in each eye, located at the front of the retina. Cones function in bright light and provide sharp, colorful daylight images. Human eyes contain about 6 million cones concentrated around the center of each retina. There are three different types of cones - red cones, green cones, and blue cones - and each type is sensitive to a different range of wavelengths of light. Different types of cones function together to interpret colors other than red, green, and blue. For instance, in order for the eye to see yellow light, red cones and green cones must work together. Nerve fibers from the rods and cones converge in a small area at the posterior part of the eyeball. This area is known as the optic disc or blind spot because it contains no photoreceptors. The convergence of nerve fibers at the blind spot forms the optic nerve, which leads to the brain. The blind spot can be located using a Blind Spot Diagram like the one at this station. Data Results

Left Eye Right Eye

Distance at which the dot disappeared (cm)

 

 

 

Station 7: Visual Compensation 

Background The retina of the eye possesses two types of specialized, light-detecting nerve cells known as photoreceptors. They are called rods and cones because of their distinctive shapes. Rods function in dim light and perceive shades of gray, like what you see when your eyes adjust to darkness. There are about 120 million rods in each eye, located at the front of the retina. Cones function in bright light and provide sharp, colorful daylight images. Human eyes contain about 6 million cones concentrated around the center of each retina. There are three different types of cones-red cones, green cones, and blue cones-and each type is sensitive to a different range of wavelengths of light. Different types of cones function together to interpret colors other than red, green, and blue. For instance, in order for the eye to see yellow light, red cones and green cones must work together. Nerve fibers from the rods and cones converge in a small area at the posterior part of the eyeball. This area is known as the optic disc or blind spot because it contains no photoreceptors. The convergence of nerve fibers at the blind spot forms the optic nerve, which leads to the brain. The blind spot can be located using a Blind Spot Diagram like the one at this station. Does your brain compensate for the loss of vision from the blind spot? In this activity, you will solve this mystery by describing the presence or absence of a white background when the dot disappears, and by observing a line that extends through and beyond the blind spot. Data Results

Describe the color of the area where the dot disappears compared to the color of the rest of the sheet of paper. Is there an absence of white where the dot was, or does the brain automatically fill in the white background when the dot disappears?

What happens to the vertical line drawn through the dot as the dot disappears into the blind spot? Does the portion of the line that passes through the dot disappear, too? Explain.

 

 

 

 

Station 8: Afterimages 

Background The retina of the human eye contains about 125 million rods and approximately 6 million cones. Both types of photoreceptors are named for their shape. Rods are more sensitive to light, but cones are responsible for color distinction. Rods are found in their greatest density in peripheral regions of the retina, whereas cones are in the middle of the visual field. In humans, each rod or cone contains a visual pigment; in rods that pigment is rhodopsin. There are three classes of cones, generally referred to by the colors red, green and blue, and each with a different visual pigment. Each of the pigments can detect a range of light wavelengths; the brain's perception of intermediate hues, or shades depends on the stimulation of two or more classes of cones. The perception of orange for example is caused by the stimulation of both the red and green cones. When the visual pigments absorb light, the molecules change shape and they no longer can detect light; they become temporarily unresponsive. It can take a few minutes for the visual pigments to return to their original shape and again can detect light. For example, the adjustment period experienced when going from bright light into darkness (or vice versa) is the amount of time that is required to resynthesize the needed pigments in the cells. In this activity, you will investigate how green-sensitive and orange-sensitive cones of the retina can be fatigued, by viewing these intense colors against a white background. Over time, the pigments in the cones are degraded and, when the color is removed, the area of the retina previously stimulated by the color is unable to respond to the less intense color contained in white light. The retina responds to all wavelengths of the spectrum other than the intense color (green or orange) stimulus. The result is an afterimage formed from the remaining colors of the spectrum. Data Results

What color is the afterimage from the orange paper strip?

What color is the afterimage from the green paper strip?

 

 

 

 

 

Station 9: Visual Accmmodation 

Background The human eye can focus at very short distances. The lens changes shape automatically to project a clear, inverted image having the proper focal length at the retina. This action is called accommodation. The closest point at which an eye can focus is termed the near point, or the minimum focal point, of vision. This can be measured by focusing on a sharply defined point and bringing it closer to the eye until it appears blurred or doubled. The distance from the eye to the object when this occurs is the near point. Data Results

Near point for right eye (cm): Near point for left eye (cm):

   

Station 10: Hearing 

Background The human ear is divided into three regions: the external, middle, and inner ear. The external ear, the part you see, gathers incoming sound waves and funnels them through the ear canal to the tympanic membrane (ear drum), which vibrates at the same frequency as the sound waves that contact it. Beyond the tympanic membrane lies the middle ear, an air-filled cavity in the temporal bone. The middle ear contains a chain of three tiny bones called the auditory ossicles: the malleus (hammer), the incus (anvil), and the stapes (stirrup). The end of the malleus is embedded in the tympanic membrane, and the stapes is attached to another membrane, the oval window, at the entrance to the inner ear. The auditory ossicles transmit sound vibrations from the tympanic membrane to the sound-sensitive portion of the inner ear. The part of the inner ear concerned with sound reception is the cochlea, a fluid-filled organ that resembles a snail's shell. Vibrations of the oval window travel through the fluid to motion-sensitive hairs. The sound-produced vibrations cause the hair cells to bend, eliciting nerve impulses that travel via the acoustic nerve to the auditory cortex in the brain. The louder the noise becomes, the higher the rate of nerve impulse traffic to the brain. Because the cochlea is embedded in a bony cavity, vibrations transmitted through the entire skull can set the cochlear fluid in motion and elicit a sensation of sound. Therefore, a tuning fork placed against any portion of the skull can be heard even when both ears are securely plugged. This phenomenon, called bone conduction, will also be tested in this activity. Data Results

Auditory Acuity Left Ear Right Ear

Distance at which sound is no longer heard (cm)

Bone Conduction

Was the sound louder on the side of the head where the tuning fork was touched? Explain you answer.

 

 

 

Station 11: Hearing 

Data Results

Two Ears Where You Stood (5 ft, 10 ft, 15 ft, etc)

Subject’s Guess of Distance (correct/not)

Trial One

Trial Two

Trial Three

One Ear Covered Where You Stood (5 ft, 10 ft, 15 ft, etc)

Subject’s Guess of Distance (correct/not)

Trial One

Trial Two

Trial Three

Which was easier - one ear or two? Using your knowledge of sound localization, explain your results.

   

Station 12: Stroop Effect 

Data Results Record your times here

Trial 1:

Trial 2:

Why was the second trial harder? What two theories explain these results? Describe them.

 

 

 

 

   

Station 13: Smell Data Results

Number of Smell Safe to Eat or Not Number of Smell Safe to Eat or Not

1 6

2 7

3 8

4 9

5 10

Which smells did you know right away? Why?

How accurate were you? What does this tell you about your sense of smell?

Some of these smells may have brought back a memory. Why does that often happen with smells?

   

Station 14: “Scent”sory Adaptation Data Results - Put the letter in the correct place

Weakest Strongest

______ ______ ______ ______ _______

Are mistakes made in the same place of the "concentration gradient"?

Are the first samples "easier" to smell than later samples? Is there any adaptation of the sense of smell?

With repeated attempts to rate the concentration, does the performance get better or worse?

   

Station 15: Touch

Data Results

Bag #  Object/Texture?  Bag #  Object/Texture? 

1 7

2 8

3 9

4 10

5 11

6 12

 

 

 

 

 

Station 16: Visual Adaptation Data Results

How many inaccurate tosses were thrown while wearing the goggles?

Once you are able to hit the target REMOVE THE GOGGLES & toss a beanbag in the bucket. What happened?

   

Station 17: Taste Data Results SKITTLES 

Color Taste Guess Actual Taste

Green

Blue

Turquoise

Red

Pink

FRUIT LOOPS 

Color Taste Guess Actual Taste

Red

Orange

Yellow

Green

Blue

Purple

OREOS 

Color Taste Guess Actual Taste

1

2

3

4

5

How significant is our sense of sight in determining what we are tasting? Explain.

How significant is our sense of smell in determining what we are tasting? Explain.

Record one thing you learned from each experiment and reading the accompanying articles at the end of the lab.