Lab report on Sensory Threshold In this lab the purpose is to test the sensory threshold of a human body. To say it in terms that are easier to understand, we are testing how accurate certain points are on a body with response to touch. We are using three points on the body, the forearm, palm, and index finger. With these three points we will be testing to see how sensitive each point on the body is by measuring the distance of which we can feel one or two points. The part of the brain that allows us to feel, the somatosensory cortex, is mapped out in relation to which parts of the body it processes its touch. Parts of our bodies have different densities of pressure receptors, the densities of these receptors correlates to the amount of brain tissue devoted to processing the somatosensory information.
The face for example has a high densities of pressure therefor the somatosensory cortex has a large amount of area for the face, compared to the leg that doesn’t have as much pressure receptors, and therefore uses a small area of the somatosensory cortex. (See illustration Fig. 511) With this information about how touch relates to the somatosensory cortex I expect that the index finger will be the point where we are the most sensitive then the palm followed by the forearm. The index finger should be able to detect the smallest distance between pokers than the palm or the forearm.
To test the threshold of the human body we took a divider with two sharp points on the end of it. With the pointer we were able to set it to different measurements. We used measurements from .25 centimeters to 4 centimeters with an increment of .25 centimeters. After me measured the distanced out we taped the individual with the point, set to a certain distance, on either ; the forearm, palm, or index finger. The individual then had to decide wether we poke them with ether one or two points. Every once and a while we would tap the individual with one point so that they wouldn’t be able to just guess that we were using two points. To keep everything on track we chose one side to do the testing on, and varied the distance of the pointer throughout the experiment and also the location of the tap.
After conducting this experiment we compiled all of the data from every PSY 201 lab class and averaged the results together to give us a larger testing group. With the data we took the average of the percent correct for each distance for each position on the body. (see fig 1.1 From the data we noticed that the index finger had the greatest sensitivity with 67% of the answers were correct at .25 centimeters. The forearm seemed to be the next sensitive at .25 centimeters with 22% answering correct. The palm seemed to be the least sensitive at the smallest distance, .25 centimeters, with only 18% getting it correct.
In the smallest distance there seems to be some what of a deviation from what the rest of the data states, because in the rest of the data the palm seems to be more sensitive with the percents being higher with correct answers, so it seems that the palm is more sensitive than the forearm. As the distance of the pointers increased so did the percent of correct answers, with a larger pint it seems as though it is easier to distinguish between on and two points. The index finger started to reach 100% correct at the distance of 1.75 centimeters, compared to the palm obtaining 100% correctness at 2.5 centimeters and the highest that the forearm ever got was 78% correct at 4 centimeters.
This data seems to show the relation to he area of the brain tissue used in the somatosensory cortex does relate to the sensitivity of a particular area. The finger has the largest area then the palm has the second most area followed by the forearm with the least area amount.
This experiment happened as I thought it would with the finger being able to detect the smallest distance followed by the palm and then the forearm. The index finger data shows that it was able to detect a tap from two points at a distance of .25 centimeters apart 67% of the time that is a very good strong average proving that it is the most sensitive of the three. In the .25 distance for the palm the average was only 18% correct, yet when tested with a poker with a distance of .5 centimeters the average percent correct jumped up to 40%. It seem as tough there was an error at this distance for the palm perhaps both pointers didn’t hit or even the tester might not of taped them good enough. This large of a jump deviates to much compared to the next increment to be correct.
The rest of the percents seem to rise a little as the size goes up by around 2% to 18% seeming like they are a normal jump. Just as I predicted the forearm is the least sensitive of the three, it never reached 100% at any distance and the numbers didn’t get very high relaying that it is the least sensitive. In my graphs you will notice a trend, that as the distance of the pokers increases so does the percent correct.(fig 1.2-1.4) This is because by increasing the distance between the pokers your touching the same pressure receptors and so they translate easier wether it was one or two. Also the percents were the highest for the Index finger followed by the palm and then the forearm and the greater sensitivity relates back to the area used in the somatosensory cortex. Perhaps to better test the points on the body we could use a smaller distance an see how small of a distance the index finger can notice this would give us a better idea how sensitive the fingers are. This data compiled from our experiment helps to support the idea that the more sensitive parts of our body use more brain tissue in the somatosensory cortex.