Name______Per______
Testing Tactile Localization
The density of the touch receptors varies significantly in different areas of the body. In general, areas that have the greatest density of tactile receptors have a heightened ability to "feel". These areas correspond to areas that receive the greatest motor innervation; thus they are also typically areas of fine motor control. Let's check it out.
Tactile localization is the ability to determine which portion of the skin has been touched. The tactile receptor field of the body periphery has a corresponding "touch" field in the brain. Some body areas are well represented with touch receptors, and tactile stimuli can be localized with great accuracy, but density of touch receptors in other body areas allows only crude discrimination.
Look at the five areas listed in the chart. Make a hypothesis that explains which area you think will have the most touch receptors. Write your hypothesis here. ______
The subject's eyes should be closed during the testing. One experimenter touches the palm of the subject's hand with a pointed black felt-tipped marker. The subject should then try to touch the exact point with his or her own marker, which should be a different color. Measure the error of localization in millimeters.
Repeat the test in the same spot twice more, recording the error of localization for each test. Average the results of the three determinations and record in the chart. Repeat for each of the five areas.
Testing Tactile Location / Error of localization (distance between marks - measured in millimeters)Body area tested / Trial 1 / Trial 2 / Trial 3 / Average
Palm of hand
Fingertip
Ventral Forearm
Back of Hand
Back of Neck
1. Does the ability to localize the stimulus improve the second time?_____ the third time?____
Explain your answer.
2. Which area has the smallest error of localization (is most sensitive to touch)?
3. Rank each of the five areas that you tested in order from most sensitive to least sensitive.
4. Below is sample data from a previous year. Rank this data from most sensitive to least sensitive.
Body Part / Average error of localizationPalm of hand / 8.5 mm
Fingertip / 5.4 mm
Ventral Forearm / 13.7 mm
Back of Hand / 11.4 mm
Back of Neck / 12.6 mm
5. Does your data agree with the sample data? Explain why or why not.
6. Based on the data complete this sentence with greater than or less than: The higher the average error of localization (distance between marks), the ______the sensitivity of that area of the body.
7. Define tactile localization.
8. Make a bar graph of YOUR data and the SAMPLE data. Make sure your graph has a title that tells what the graph is showing. Label the x and y axis and include unit of measurement on the y-axis. Use different colors to represent your data and the sample data.
8. Write a conclusion that relates the number of touch receptors in the skin to the level of sensitivity. Include a sentence about your hypothesis (was it correct or incorrect).
9. Explain what touch receptors do.
10. Using your knowledge of anatomy and physiology of the skin, explain why a person's fingertips are more sensitive to touch than their forearms. Include the term touch receptors.
11. Each box below represents an area of skin. One is from a highly sensitive area (fingertip), the other is from an area that is not very sensitive (forearm). Using hearts to represent touch receptors, fill in the boxes below to show the relationship between the number of touch receptors and the level of sensitivity.