Pre-lab Reading
How you relate to the world is in large part a reaction to sensory input from the world around you, such as what you see, hear, smell, touch, and taste. All animals have senses but they have evolved differently for each species depending on the selection pressures in their local environ-ment. For example, many animals that live in caves, like cave salamanders and fish, have reduced vision due to a lack of light. Yet many of them also have heightened senses of hearing which help them to gather information in a light-deprived environment.
When a sensory input like a sound or smell is encountered, sensory receptors generate impulses that are transmitted to sensory neurons, which carry the impulses to the brain or spinal cord. Finally, interneurons carry the impulses to the sensory interpretive centers, such as hearing, vision, or smell, in the brain. The cerebral cortex of the brain interprets the impulses and sends information to motor neurons in the body about how to respond to the sensory input.
Sight
Light waves reflect off of objects and are bent as they enter the cornea. Between the cornea and the lens is a fluid called the aqueous humor. The light waves continue through the pupil (the size of which is controlled by the iris) and lens where they become focused on the retina. The inner eye, between the lens and the retina, is a jellylike fluid called the vitreous humor. On the retina photoreceptors transmit impulses to the visual center in the brain where they are interpreted as visual images. Rods and cones are specific kinds of photoreceptors. Rods are involved in black and white visual information, while cones are used in color vision. Human eyes can gain information from the visible light spectrum, at wavelengths of 400–700 nanometers. Many other species can see other aspects of the visual spectrum such as UV light.
Hearing
Ears contain receptors for sound stimuli as well as ones that help maintain equilibrium. The ear contains three parts: the outer, middle, and inner ear. The outer ear, or pinna, encounters sound waves that are transmitted through the air and then funneled toward the auditory canal, which leads toward the eardrum. In the middle ear, the sound waves cause vibrations in the eardrum which causes the three small bones [the malleus (attached to ear drum), incus, and stapes] of the inner ear to vibrate and transmit sounds to the cochlea. The vestibule is the large portion at the base of the cochlea and is in contact with the stapes. The snail-shaped cochlea in turn causes movements in the basilar membrane. These final movements transmit signals to the hearing center of the brain. The inner ear, the vestibule, also contains receptors that inform the brain about the position of the head and body, which is how the ear informs us about our equilibrium.
Taste
Taste occurs in the mouth and is the result of special epithelial cells called chemoreceptors. Have you ever wondered why food tastes blander when you have a head cold? It is because taste is a combina-tion of both taste and smell; thus, when you have a cold, scents can’t reach the sensory receptors for smell. There are five basic tastes: sweet, sour, bitter, salty, and umami (savory).
Touch
The ability to sense touch in humans is governed by the somatosensory system. This system is comprised of a network of various specialized receptors located mainly in the skin as well as few other locations. There are four main types of somatosensory receptors in the body: thermoreceptors (temperature), nociceptors (pain), mechanoreceptors (pressure and vibration), and proprioceptors (sense of space). The function of all sensory receptors is greatly influenced by a process called sen-sory adaptation, where the responsiveness of the receptor decreases over time in the presence of a constant stimulus.
Online Lab 4: Materials, Methods, and Procedures
Materials
• Online colorblindness test chart and online assessment too
l • Measuring tape or tool (see instructor demo)
• Tape
• Online blind spot test chart
• Negative afterimage charts
• Timer/stopwatch (on phone is fine)
• Door frame (as in your house)
• Three containers large enough to submerge both hands at the same time
Water at three different temperatures:
• Warm (not hot or scalding!)
• Room temperature
• Cold (add a few ice cubes to room temperature water)
• Decibel meter or sound meter app on smartphone (see instructor suggestions)
Methods Sight
I. Colorblindness
1. View the online colorblindness test chart. What shapes do you see?
2. Record your observations in the datasheet.
3. Your lab instructor will direct you to an online color blindness assessment. Complete the test and record your score in the datasheet.
II. Blind Spot Vertebrate animals all possess a small region in the eye where the optic nerve passes through the optic disk. There are no photoreceptors at this point of the retina, resulting in a small part of the visual field of each eye that is blind.
1. Tape three sheets of paper together and mark off 120 cm, as shown in the instructor’s demon-stration. Tape the measuring sheet to a wall at the height of your head.
2. Load the blind spot finder slides to your laptop or phone. 3. Stand so that your eye is lined up with the 1 cm mark (the measuring sheet should be either at your right or left side, and you should be looking toward the 120 cm mark).
4. Hold the phone or laptop out in front of you at around the 100 cm mark. 5. Focus your gaze on the black x. 6. Slowly bring the image closer to you.
7. Stop when the black dot (or the mouse) disappears. Record the distance between your eye and the image using the measuring chart.
8. Switch eyes and repeat steps 3–7.
9. Can you detect your blind spot if both eyes are open when you do the test?
III. Physiological Afterimage Physiological afterimages are an example of local adaptation, in this case a change in response/ sensitivity of photoreceptors in a restricted region of the retina. Your instructor will give you three online slides to test the physiological afterimage effect. It is best to view these slides on a computer or laptop screen rather than on a phone.
Afterimage Effect #1
1. Set up your stopwatch so you are ready to start timing in step 3 without having to look at the stopwatch.
2. Cover your left eye and gaze with your right eye at the white dot in the image on the left side of the screen and count slowly to 30.
3. Move your gaze to the black dot in the center of the image on the right side of the screen and begin the stopwatch.
4. Record the time when the afterimage disappears and answer the questions in the datasheet.
5. Repeat steps 1–4 while covering your right eye.
Afterimage Effect #2
1. Cover your left eye. Gaze at the black dots in the eyes of the human pictured on the left side of the screen. Count slowly to 50.
2. Shift your gaze to the black ‘x’ on the right side of the screen, and count to 30. 3. Record your observations on the datasheet.
4. Repeat steps 1–3 covering your right eye and without covering either eye. Answer the questions in the datasheet.
Afterimage Effect #3
1. This effect uses two slides: a phrase in red letters on the green background, and white slide. Make the slides full screen. With both eyes open, gaze at the second word on the first slide for a slow count of 30, and then quickly advance to the second (white) slide.
2. Record your observations in the datasheet.
Touch
I. Proprioception Kohnstamm’s Phenomenon
1. Stand in the center of a doorway. With your palms facing toward your body, firmly press the backs of your hands and wrists against the door frame. Alternatively, stand about six inches from a wall. Press the back of your right (or left) hand against the wall with firm, steady pressure.
2. Hold the pressure for a slow count of 40.
3. Step away from the doorway/wall. What happens to your arm? Slowly lower your arm(s). Wait a moment and relax your arm(s) again.
4. Repeat steps 1–3, but this time try and force your arm(s) to remain at your side(s).
5. Record your observations in the data sheet.
I. Thermoreception 1. Before you proceed with this experiment, fill out the hypothesis and prediction sections of your datasheet.
2. Submerge your right hand in the container with cold water. 3. Submerge your left hand in the container with warm water.
4. Note your observations when you first place your hands in the water and after 3 minutes. Record the observations in your data sheet.
5. Remove both hands from the cold or warm water and place both hands together in the container of room temperature water.
6. Note your observations when you first place both hands in room temperature water and after 3 minutes.
Hearing and Sound
1. View the video demonstration of the Weber and Rhine tests. Answer the questions in the datasheet.
2. Measure the intensity of sounds in your physical environment using a decibel meter on your phone. Try to find at least three examples each of what you consider to be 1) soft sounds, 2) medium-loud sounds, and 3) very loud sounds you can find. Be sure to remove yourself imme-diately from any environment with a sound that is physically uncomfortable.
3. Record the measurements in the datasheet. 4. Answer the questions in the datasheet.