Chapter 3 Lab, Page 1 of 1
LAB 1 (CHAPTER 3): SOMATOSENSORY PERCEPTION
(graded out of 40, worth 10% of final grade)
This lab consists of two parts. You will need someone to act as an observer (participant) for both parts. This can be room-mate, sibling, etc. If you don’t have access to a partner, let me know and we can a
ange an alternative assignment.
Equipment Required
Part 1:
· A compass, the kind with two points. Alternatively, take a paperclip (the regular "trombone" kind), unbend it so that it's a (relatively) straight piece of wire, then bend it into a skinny "U shape".
· A ruler with millimeters marked.
Part 2:
· 10 small common objects that can be identified by touch.
· A stopwatch or equivalent
Handing In
Hand in your lab as follows:
1. Fill out this document in the spaces provided
2. Save it as "Lab1YourNameStudent#.docx"
(e.g., Lab1CharlesCollin123456.docx). It's okay if it's .doc format.
3. Send it via email to the TA (see syllabus for email address)
4. Use the subject line: PSY3108X Lab1, YourName StudentNumbe
(e.g., PSY3108A Lab1, Charles Collin 123456)
Failure to follow these instructions properly will lead to a 10% mark deduction, so be careful!
Part 1: Measuring Two-Point Threshold by Method of Limits (25 marks)
In this part of the lab, you will measure three absolute thresholds using the classic Method of Limits. In preparation, you should review the material in Chapter 1 (Lectures 2-4) on psychophysical methods and thresholds, focusing especially on the Method of Limits, as well as the section in Chapter 3 (Lectures 5-7) on measuring two-point thresholds.
Method:
1. Experimenter and observer should sit at a table across from one another in a quiet area without distractions.
Experimenter: Adjust the compass so that its points are 10 mm apart.
Observer: Lay your right arm on the table, palm up, fingers outstretched. If wearing long sleeves, roll the right one up to the elbow. Close your eyes.
2. Experimenter: You'll be testing the participant's ability to distinguish between one-point and two-point skin contact at a variety of distances. On each trial, flip a coin. If it is heads, then do two-points, then one. If tails, do one point, then two. That is, if you got heads, then touch both points of the compass to the observer's skin first, then touch just one point. In all cases, apply only gentle pressure; just enough to slightly dent the skin. When doing two-points, make sure both points touch at the same time. Ask the observer if she feels two points on the first touch or the second. This is called a temporal 2AFC task. Record whether her answer was co
ect (Y or N) in the grid at the end of this section.
Observer: Do your best to report whether you felt two points on the first touch or the second. If you're unsure, guess.
3. Experimenter: Adjust the distance between the two points to 8 mm and repeat the procedure, asking whether the observer feels two points on the first touch or the second. Continue this way, reducing the distance by 2 mm each time until the observer makes a mistake. This completes the first run, which is a descending run.
4. Next, complete an ascending run. That is, start with the points of the compass 2 mm apart (or as close as they can go), and go up by 2 mm increments until the observer reports feeling two points separately.
5. Complete a total of two descending runs and two ascending runs. Calculate the thresholds for each run, and the overall threshold for the four runs.
6. Repeat the entire above procedure—four runs, alternating between ascending and descending—for the palm of the hand. Touch the points right in the centre of the palm. However, this time start descending runs at 20 mm and go by steps of 4 mm.
7. Repeat the entire procedure—four runs, alternating between ascending and descending—for the forearm. Touch the points about 5 cm down from the inside of the elbow. However, this time start descending runs at 60 mm and go by steps of 10 mm.
NOTE: If the maximum values given above (10 mm for finger, 20 for palm, 60 for forearm) are not sufficient for the observer to feel two points, then go beyond this, trying larger increments, until she is able to feel two points. If the observer is still co
ect at the minimum, go below this until she makes a mistake. If the observer still gets the answer co
ect on the finger tip when the points are 2 mm apart, then mark the threshold for that run as 1 mm.
Results: Enter subject responses in the following grids. Using the procedure we went over in class, calculate the threshold for each run and the overall threshold.
FINGERTIP
Run 1
Run 2
Run 3
Run 4
2-point Dist.
10mm
Y
Y
Y
Y
8mm
Y
Y
Y
Y
6mm
Y
Y
Y
Y
4mm
Y
Y
Y
Y
2mm
Y
Y
N
Y
Threshold:
1mm
1mm
4mm
1mm
Average Threshold = XXXXXXXXXX) / 4
= 1.75mm
PALM
Run 1
Run 2
Run 3
Run 4
2-point Dist.
20mm
Y
Y
Y
Y
16mm
Y
Y
Y
Y
12mm
Y
Y
Y
Y
8mm
Y
Y
Y
Y
4mm
Y
Y
Y
Y
2mm
N
Y
Y
Y
Threshold:
4mm
1mm
1mm
1mm
Average Threshold = XXXXXXXXXX) / 4
= 1.75mm
FOREARM
Run 1
Run 2
Run 3
Run 4
2-point Dist.
60mm
Y
Y
Y
Y
50mm
Y
Y
Y
Y
40mm
Y
Y
Y
N
30mm
N
Y
Y
Y
20mm
Y
Y
Y
Y
10mm
Y
N
N
Y
5mm
N
Y
N
Y
Threshold:
10
4
20
4
Average Threshold = XXXXXXXXXX)/4
= 9.5mm
Graph: The average spacing between SA1 receptors in the skin varies according to the area examined. At the fingertip is 1.1 mm. It is 3.5 mm on the palm and 37.0 mm on the forearm. Produce a graph showing the relationship between the two point thresholds measured above and these receptor densities. You can either draw a graph using drawing software, produce one using Excel if you know how to do that, or just draw it on paper, take a picture and paste it in. In any case, paste in the graph below.
Fingertips
Palm
Forearm
Discussion: Briefly discuss your results below. What do these results tell you about how differences in tactile acuity arise? How do your results compare with those given in Chapter 3 (see esp. Lecture 6, slide 25). Do your results agree with the Law of Outward Mobility?
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Part 2: Time to Identify Common Objects by Touch (15 marks)
In preparation for this part of the lab, you should review Chapter 3, especially Lecture 7, slides 8 to 12.
Also, you should find ten small common objects. Do not reveal these to the observer. These can be any small objects, such a cup, a ruler, a pen, a glove, a calculator, etc. Careful! The objects must not be fragile, sharp, or otherwise dangerous or unpleasant to touch.
Procedure: Sit at a table across from one-another.
Observer: Put your hands, palms down, on the table in front of you, about 30 cm apart. Close your eyes. When prompted by the experimenter,
ing your hands together and attempt to identify the object placed between them as quickly as possible. When you think you know what it is, say the name.
Experimenter: For each object, do the following: Place it on the table between the observer's hands and get ready with the stopwatch. Tell the observer to begin ("Ready? Set. Go."). Start the stopwatch as soon as the observer makes contact with the object, and stop it as soon as she says the name of the object. Prepare to be quick, it will often take only a second or two!
If the observer gives the co
ect answer, mark the time to identify the object in the grid at the end of this section.
If the observer states an inco
ect answer, mark an X on the data sheet and do not include this trial in your analyses (this should happen pretty rarely or else you've chosen some overly difficult objects!).
In addition to timing the observer's identifications, watch as she identifies the object, attempting to note which haptic exploration procedures are used. See Lecture 7 for some of the most common ones.
Results:
Object
Time to ID
Exploration procedures employed
Hair clip
1.67
Enclosure and Lateral motion
deodorant
1.31
Enclosure, pleasure, unsupported holding
Debit card
2.59
Lateral motion and unsupported holding
tiara
2.21
Lateral motion and contour following
Water bottle
1.07
Enclosure and static contact
Vaseline
2.47
Contour following and enclosure
Chapstick
2.07
Unsupported holding and enclosure
Pencil case
.98
Lateral motion
Sleep mask
1.75
Pressure and enclosure
Nail polish
1.66
Unsupported holding and enclosure
Discussion: What was the average time taken to identify the objects? How does your value compare to that reported in Klatzky, Lederman & Metzger, (1985)? What were your general observations regarding haptic exploratory techniques? Were any more common than others? Was there any suggestion of a relationship between the type of object and the type of technique used? Did you notice any techniques that Lederman & Klatzky XXXXXXXXXXdid not describe?
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