Homework 5 - due Thursday 7/6

2- point Thresholds

Do the following demonstration and then answer the following questions.

You are going to be testing what the threshold is for detecting if two points are touching the skin. If you touch the skin simultaneously with 2 points and it feels like just one, then that distance between the points is below threshold for detection. If you touch the skin with 2 points and it does feel like two separate points then that distance is above threshold. You are going to find the threshold for 2 point detection on different parts of the skin. For this you will need a person to serve as the participant, and you will be the experimenter.

Materials needed:

2 toothpicks with pointy tips or two mechanical pencils

a pencil to record the data

a piece of paper

Procedure: (method of limits)- do the following for the fingertip, palm, and inside of arm near elbow(see exact placement on diagram below)

1. Trace the participant's hand onto a separate sheet of paper (palm up). It should resemble the diagram above.

2. Have the participant close his/her eyes (they cannot look at the points touching the skin).

3. Take two toothpicks (or two mechanical pencils), and pull them a few inches apart.

4. Keep the distance constant between the two. At the same time, briefly touch the two points to the skin and release. (see diagram for the 3 locations)

Only touch the skin for about 1 second. Do not hold the points in place on the skin. Try to touch the skin with the 2 points at the same time (not one then the other).

5. Ask the participant if it felt like 1 point or 2. (they may know that 2 points are touching them, but they are to report if it feels like 1 or 2)

If it felt like 2, slightly decrease the distance between the 2 points and repeat steps 3 & 4.

If it felt like 1, slightly increase the distance between the 2 points and repeat steps 3 & 4.

-continue until you find the distance just on the border where they can feel it as 2.

6. When you find the distance between the 2 points that is at the threshold for detecting 2 points, mark that distance on the hand diagram that you first traced. (e.g. |------------| would be the mark if that's how far apart the two points were at a particular location or |---| if only that far apart). This represents the distance between the 2 points at the threshold for discriminating the 2 points).

7. Repeat the whole procedure for each skin location (fingertip, wrist, and inside of arm near elbow).

8. Choose one more location on the body (your choice of where), and do the same procedure on that location.

Questions to answer: (typed) -- MAKE SURE TO TURN IN YOUR HAND DRAWING

1. In your own words, explain what the 2 points threshold for discrimination is (i.e. what this demonstration is illustrating).

2. At what location was discrimination of the 2 points the best when comparing the fingertip, palm, and wrist? How did your 4th location (the one of your choosing) compare to those other locations?

3. What does this mean for our ability to detect fine discriminations at different locations on the arm and body? Why do you think some locations better than others?

4. What does this tell us about how easily would a blind person be able to read braille type with his/her arm as opposed to the fingertip?