Somatosensation Using Two Point Thresholds Lab Report
Somatosensation Lab Using Two Point Thresholds
Alex Mendelson
2/24/2014
Two Point Thresholds This week in Sensation and Perception Lab we performed a lab that measured an individual’s somatosensation, which is their sense of touch. In order to measure the sense of touch we manipulated the thresholds of sensation by using the two point threshold procedure. The two point threshold procedure measures the smallest distance of two separate but adjacent points of stimulation on the skin that produces two distinct points of sensation. The touch receptors that are being manipulated in this experiment are nerve cells that relay information to your brain about a physical sensation. Specifically, we are manipulating mechanoreceptors …show more content…
which respond to mechanical pressure or distortion, in this case on the skin. Somatosensation receptors are located throughout the entire body inside of the skin tissue.
Many of the mechanoreceptors are found near hair follicles and are excited when these hair follicles move. Receptors in the skin can both be found near the surface or in deeper tissue; in our two point threshold test we were testing which receptors on different parts of the body were at different depths of the skin. The Type I receptors are located shallow in the skin at the dermal-epidermal boundary, requires a low threshold of stimulation to feel and has a smaller receptive field. Type II receptors are located deep in the dermal tissue, has higher thresholds of stimulation and have large receptive fields. Once the touch receptors are stimulated, the information is transduced into an electrical and chemical message that sends information to our brain and back to our limbs as a response. The skin areas are represented in the brain in neighboring areas on the somatosensory cortex. The structure known as the homunucleus reflects the relative space that our body parts occupy on the somatosensory and motor cortices. In an experiment by Craig and Johnson in 2000, they used two different methods to manipulate the two point threshold: subjective and objective. In the subjective method, the subjects are presented …show more content…
with two points of stimulation at varying distances and the subjects are asked to make a judgment on the perceived experience. In the objective method, two points are stimulated only in some trials while one point is stimulated in others and subjects are asked whether one or two points were presented. Craig and Johnson wanted to try this because their research suggested that the data resulting from the two point threshold technique was not consistent. In our experiment we only used the subjective method of manipulating the two point threshold and to increase reliability we repeated each area we tested.
Methods
This experiment used the two point threshold method of point localization.
The purpose of this lab was to determine the participant’s two point threshold for the finger, palm, forearm, and back. The experimenter used a dial caliper as the tool to deliver a stimulus to the participant. The following increments were used when adjusting the caliper on each body part: finger 0.01 inches, palm 0.05 inches, forearm 0.1 inches, back 0.1 inches. To accurately record the threshold for each body part manipulated, the following conversions were used for the dial caliper: 10 on the watch dial = 0.01 inches, 50 on the watch dial = 0.05 inches, 100 on the watch dial = 0.1 inches. The experimenter used the sharper tips on the caliper and when applying pressure onto the skin the experimenter made sure that both tips touched the participant’s skin at the same time and each applied the same amount of pressure. This lab used the method of limits and recorded the two consecutive points in which the participant felt two stimulus points and recorded the first as the threshold. These thresholds were recorded for ascending trials only. Each body part (finger, palm, forearm, back) was manipulated in three trails each. The participant was not to watch the delivery of the caliper tips during these trials. In order to accurately record the thresholds, the participant was to clearly state if each application of pressure yielded the sensation of one or two points on each body
part.
Results After recording each threshold from the two point test the mean ascending thresholds were calculated for each body part. The mean thresholds obtained were as follows: finger = 0.09 inches, palm = 0.23 inches, forearm = 0.33 inches, back = 0.47 inches. The means were found by adding the threshold from each of the three trials, and dividing that number by the number of trilas (three). As an example, the mean threshold for the finger was calculated as follows:( 0.1+.0.7+0.09)/3 =0.087 rounded to 0.09. Each of the means represents the threshold of stimulation necessary for the participant to feel two separate points applying pressure on their skin.
Table 1. Mean Threshold for Two Point Test per Body Part
Discussion The results of the data indicate a variation in mean threshold of the participant. The graph shows a pattern regarding mean thresholds per body part and the different caliper manipulations. The positive nature of the graph shows an increase in space required to reach the threshold for each body part as indicated in Table 1. The finger required the smallest distance to reach threshold, followed by the palm, forearm and the largest distance to threshold was the back. This indicates that the finger has more Type I receptors that respond to stimuli near the outer layers of the skin. Mean thresholds for the forearm and back may indicate more type II receptors since a higher threshold was required to reach sensation. Problems experienced with the experiment could include the consistency of the caliper prodding. On multiple occasions the experimenter used the same caliper measurement on the participant in result of the participant being unsure if one or two points were felt. This could be solved by giving the participant one chance per increasing increment on the caliper. Another problem that may arise could be that by the third round of ascending trials the sensitivity of the skin area on each body part may be affected. After repeated stimulations of each point, the receptors could have become more sensitive or desensitized. I do not believe this aspect of the experiment could be changed due to the nature of human skin and different receptors being present all over the body. The data collected fulfills the purpose of the lab: to determine the participant’s two pint threshold for the finger, palm, forearm and back. The participant’s two point threshold for each part of the body resembles the relative magnitude of the example bar graph given to us in lab which indicates typical results. Referring back to Craig and Johnson in 2000, the subjective method that we used to manipulate the two point threshold produced the consistent results that we hoped to achieve.
References
Craig, J. C., & Johnson, K. O. (2000). The Two-Point Threshold Not a Measure of Tactile Spatial Resolution. Current Directions in Psychological Science, 9(1), 29-32.
Finger Palm Forearm Back
A1
A2
A3
A1
A2
A3
A1
A2
A3
A1
A2
A3
0.2 in
1.0 in
2.0 in
2.0 in
0.19 in
0.95 in
1.9 in
1.9 in
0.18 in
0.9 in
1.8 in
1.8 in
0.17 in
0.85 in
1.7 in
1.7 in
0.15 in
0.8 in
1.6 in
1.6 in
0.15 in
0.75 in
1.5 in
1.5 in
0.14 in
0.7 in
1.4 in
1.4 in
0.13 in
0.65 in
1.3 in
1.3 in
0.12 in
0.6 in
1.2 in
1.2 in
0.11 in
0.55 in
1.1 in
1.1 in
0.1 in x 0.5 in
1.0 in
1.0 in
0.09 in
x
0.45 in
0.9 in
0.9 in
0.08 in
0.4 in
0.8 in
0.8 in
0.07 in
x
0.35 in
0.7 in
0.7 in
0.06 in
0.3 in
0.6 in
x
0.6 in
x
0.05 in
0.25 in x x
0.5 in
0.5 in
0.04 in
0.2 in
x
0.4 in
0.4 in x x
0.03 in
0.15 in
0.3 in
0.3 in
0.02 in
0.1 in
0.2 in x x
0.2 in
0.01 in
0.05 in
0.1 in
0.1 in
Thres.
Thres.
Thres.
Thres.
Mean
.09
Mean
.23
Mean
.33
Mean
.47
Table 2. Raw Data
Alex Mendelson
2/24/2014
Two Point Thresholds This week in Sensation and Perception Lab we performed a lab that measured an individual’s somatosensation, which is their sense of touch. In order to measure the sense of touch we manipulated the thresholds of sensation by using the two point threshold procedure. The two point threshold procedure measures the smallest distance of two separate but adjacent points of stimulation on the skin that produces two distinct points of sensation. The touch receptors that are being manipulated in this experiment are nerve cells that relay information to your brain about a physical sensation. Specifically, we are manipulating mechanoreceptors …show more content…
which respond to mechanical pressure or distortion, in this case on the skin. Somatosensation receptors are located throughout the entire body inside of the skin tissue.
Many of the mechanoreceptors are found near hair follicles and are excited when these hair follicles move. Receptors in the skin can both be found near the surface or in deeper tissue; in our two point threshold test we were testing which receptors on different parts of the body were at different depths of the skin. The Type I receptors are located shallow in the skin at the dermal-epidermal boundary, requires a low threshold of stimulation to feel and has a smaller receptive field. Type II receptors are located deep in the dermal tissue, has higher thresholds of stimulation and have large receptive fields. Once the touch receptors are stimulated, the information is transduced into an electrical and chemical message that sends information to our brain and back to our limbs as a response. The skin areas are represented in the brain in neighboring areas on the somatosensory cortex. The structure known as the homunucleus reflects the relative space that our body parts occupy on the somatosensory and motor cortices. In an experiment by Craig and Johnson in 2000, they used two different methods to manipulate the two point threshold: subjective and objective. In the subjective method, the subjects are presented …show more content…
with two points of stimulation at varying distances and the subjects are asked to make a judgment on the perceived experience. In the objective method, two points are stimulated only in some trials while one point is stimulated in others and subjects are asked whether one or two points were presented. Craig and Johnson wanted to try this because their research suggested that the data resulting from the two point threshold technique was not consistent. In our experiment we only used the subjective method of manipulating the two point threshold and to increase reliability we repeated each area we tested.
Methods
This experiment used the two point threshold method of point localization.
The purpose of this lab was to determine the participant’s two point threshold for the finger, palm, forearm, and back. The experimenter used a dial caliper as the tool to deliver a stimulus to the participant. The following increments were used when adjusting the caliper on each body part: finger 0.01 inches, palm 0.05 inches, forearm 0.1 inches, back 0.1 inches. To accurately record the threshold for each body part manipulated, the following conversions were used for the dial caliper: 10 on the watch dial = 0.01 inches, 50 on the watch dial = 0.05 inches, 100 on the watch dial = 0.1 inches. The experimenter used the sharper tips on the caliper and when applying pressure onto the skin the experimenter made sure that both tips touched the participant’s skin at the same time and each applied the same amount of pressure. This lab used the method of limits and recorded the two consecutive points in which the participant felt two stimulus points and recorded the first as the threshold. These thresholds were recorded for ascending trials only. Each body part (finger, palm, forearm, back) was manipulated in three trails each. The participant was not to watch the delivery of the caliper tips during these trials. In order to accurately record the thresholds, the participant was to clearly state if each application of pressure yielded the sensation of one or two points on each body
part.
Results After recording each threshold from the two point test the mean ascending thresholds were calculated for each body part. The mean thresholds obtained were as follows: finger = 0.09 inches, palm = 0.23 inches, forearm = 0.33 inches, back = 0.47 inches. The means were found by adding the threshold from each of the three trials, and dividing that number by the number of trilas (three). As an example, the mean threshold for the finger was calculated as follows:( 0.1+.0.7+0.09)/3 =0.087 rounded to 0.09. Each of the means represents the threshold of stimulation necessary for the participant to feel two separate points applying pressure on their skin.
Table 1. Mean Threshold for Two Point Test per Body Part
Discussion The results of the data indicate a variation in mean threshold of the participant. The graph shows a pattern regarding mean thresholds per body part and the different caliper manipulations. The positive nature of the graph shows an increase in space required to reach the threshold for each body part as indicated in Table 1. The finger required the smallest distance to reach threshold, followed by the palm, forearm and the largest distance to threshold was the back. This indicates that the finger has more Type I receptors that respond to stimuli near the outer layers of the skin. Mean thresholds for the forearm and back may indicate more type II receptors since a higher threshold was required to reach sensation. Problems experienced with the experiment could include the consistency of the caliper prodding. On multiple occasions the experimenter used the same caliper measurement on the participant in result of the participant being unsure if one or two points were felt. This could be solved by giving the participant one chance per increasing increment on the caliper. Another problem that may arise could be that by the third round of ascending trials the sensitivity of the skin area on each body part may be affected. After repeated stimulations of each point, the receptors could have become more sensitive or desensitized. I do not believe this aspect of the experiment could be changed due to the nature of human skin and different receptors being present all over the body. The data collected fulfills the purpose of the lab: to determine the participant’s two pint threshold for the finger, palm, forearm and back. The participant’s two point threshold for each part of the body resembles the relative magnitude of the example bar graph given to us in lab which indicates typical results. Referring back to Craig and Johnson in 2000, the subjective method that we used to manipulate the two point threshold produced the consistent results that we hoped to achieve.
References
Craig, J. C., & Johnson, K. O. (2000). The Two-Point Threshold Not a Measure of Tactile Spatial Resolution. Current Directions in Psychological Science, 9(1), 29-32.
Finger Palm Forearm Back
A1
A2
A3
A1
A2
A3
A1
A2
A3
A1
A2
A3
0.2 in
1.0 in
2.0 in
2.0 in
0.19 in
0.95 in
1.9 in
1.9 in
0.18 in
0.9 in
1.8 in
1.8 in
0.17 in
0.85 in
1.7 in
1.7 in
0.15 in
0.8 in
1.6 in
1.6 in
0.15 in
0.75 in
1.5 in
1.5 in
0.14 in
0.7 in
1.4 in
1.4 in
0.13 in
0.65 in
1.3 in
1.3 in
0.12 in
0.6 in
1.2 in
1.2 in
0.11 in
0.55 in
1.1 in
1.1 in
0.1 in x 0.5 in
1.0 in
1.0 in
0.09 in
x
0.45 in
0.9 in
0.9 in
0.08 in
0.4 in
0.8 in
0.8 in
0.07 in
x
0.35 in
0.7 in
0.7 in
0.06 in
0.3 in
0.6 in
x
0.6 in
x
0.05 in
0.25 in x x
0.5 in
0.5 in
0.04 in
0.2 in
x
0.4 in
0.4 in x x
0.03 in
0.15 in
0.3 in
0.3 in
0.02 in
0.1 in
0.2 in x x
0.2 in
0.01 in
0.05 in
0.1 in
0.1 in
Thres.
Thres.
Thres.
Thres.
Mean
.09
Mean
.23
Mean
.33
Mean
.47
Table 2. Raw Data