Sensory Physiology - Tactile Localization

Name __________________________________________

Hour ________

Date ________________

SENSORY PHYSIOLOGY – Tactile Localization Tactile localization is the perception of a stimulus at a specific location on the body. The precision of locating the origin of the stimulus is associated with the stimulus intensity as well as the receptor density at the stimulus location. The more densely the receptors are located to one another, the more precisely you would expect to locate the point of stimulation. Since receptors are not distributed evenly across the skin, different parts of the body have different capacities to locate the stimulus. In this activity, we will attempt to determine areas of the body which may contain higher numbers of receptors.

PROCEDURE 1. The subject must sit with his or her eyes closed. 2. The tester should have one toothpick; the subject should have the second toothpick in their dominant hand. 3. The tester should touch the back of their partner’s non-dominant hand with the point of their toothpick and leave it there, keeping it in one location. 4. The subject will take their toothpick and carefully attempt to touch the same spot. 5. When both toothpicks are on the back of the hand, measure the distance (in millimeters) between the two. This is known as the error of localization. Record this distance in the table. 6. Repeat the procedure using the same body part, but at a slightly different location. 7. Average the two distances measured between the two trials. 8. Attempt this procedure again, this time the subject should hold the toothpick in their non-dominant hand. 9. Continue this same procedure for each of the remaining body locations listed in the chart. 10. When both partners are finished, each person should use their own data to create a bar graph, plotting the average distance, and answer the questions that follow.

Name __________________________________________

Hour ________

Date ________________

Data Table Dominant Hand 1 Trial 2nd Trial Average

Body Part

Non-dominant Hand 1 Trial 2nd Trial Average

st

st

Back of Hand Palm of Hand Inside of Forearm Outside of Forearm Outside of Upper Arm Front of Lower Leg (Shin) Back of Lower Leg (Calf)

Tactile Localization v. Distance (mm) 30

D = Dominant Hand N = Non-dominant Hand

25

20

15

10

5

0

D

N

Back of Hand

D

N Palm

D

N

Forearm (Inside)

D

N

Forearm (Outside)

D

N

Upper Arm

D

N Shin

D

N Calf

Name __________________________________________

Hour ________

Date ________________

ANALYSIS 1. As you observe the tactile localization distances measured, how do different areas of the skin compare? Are they the same? Do they vary? Briefly describe your answer. __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ 2. How do your results compare with those of other groups and individuals? __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ 3. Is the ability to localize a touch in a region related to how densely the touch receptors are located in a particular region? Briefly explain your answer. __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ 4. Does learning or experience modify the accuracy of localization? __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ 5. Did you find a difference between the tactile localization of your dominant and non-dominant hands? This is likely not due to a difference in the concentration of touch receptors. What other factors might contribute to this difference? __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ 6. Using your knowledge from the two-point sensory activity and this one, which regions not tested would likely produce a very accurate tactile localization? Briefly explain your answer. __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________