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
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
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