Two-Point Threshold: Measuring the Sensitivity of the Somatosensory System | Cheat Sheet Psychology

Experiment 5:

Two-point threshold

Aim:

To measure the two-point threshold of the subject.

Introduction:

According to the American Psychological Association the smallest distance between two

points of stimulation on the skin at which the two stimuli are perceived as two stimuli rather

than as a single stimulus.

Somatosensory system:The somatosensory system is the largest sensing system in your

body. This system produces sensory feedback whenever you come in physical contact with

your environment. These sensory feedbacks include body position (proprioception), sensing

movement of your body and limbs (kinesthesis), pain (nociception), temperature, and finally

touch.

The skin (cutaneous system) is a very important part of the somatosensory system; it keeps

bacteria out, fluids in, and helps maintain your body's structural integrity. Furthermore, it

provides your nervous system and brain with important information gathered from

the receptors embedded in your skin. Here are a few examples:

1. As you touch a hot stove, pain receptors in your skin fire signals forcing you to

immediately pull your hand away from danger. Note that this movement occurs

before you are ever conscious of the pain.

2. When you play a violin or guitar, as you become better at playing the instrument, you

can play it without looking at the strings (remember the first time you tried, and you

had to look at the neck of the guitar to play it). Without looking at your arm and

fingers, you always know where they are anyway. For example, close your eyes

and touch your nose, ear, and eye.

You can complete routine and complex tasks, because of a proper working cutaneous system.

Receptors found in your skin are the foundation of this system. Thermoreceptors give your

skin the feeling of hot and cold, nociceptors allow you to feel pain, and mechanoreceptors

respond to various pressures, vibrations and stretching of the skin. Your hypodermis. The

epidermis is the outermost layer and is just layers of dead skin that are constantly being shed

off and replaced.

Two-point threshold/ Two-point discrimination

It is the ability to discern those two nearby objects touching the skin are truly two distinct

points, not one. It is often tested with two sharp points during a neurological examination and

is assumed to reflect how finely innervated an area of skin is. In clinical settings, two-point

discrimination is a widely used technique for assessing tactile perception. It relies on the

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Experiment 5:

Two-point threshold

Aim:

To measure the two-point threshold of the subject.

Introduction:

According to the American Psychological Association the smallest distance between two points of stimulation on the skin at which the two stimuli are perceived as two stimuli rather than as a single stimulus. Somatosensory system: The somatosensory system is the largest sensing system in your body. This system produces sensory feedback whenever you come in physical contact with your environment. These sensory feedbacks include body position (proprioception), sensing movement of your body and limbs (kinesthesis), pain (nociception), temperature, and finally touch. The skin (cutaneous system) is a very important part of the somatosensory system; it keeps bacteria out, fluids in, and helps maintain your body's structural integrity. Furthermore, it provides your nervous system and brain with important information gathered from the receptors embedded in your skin. Here are a few examples:

As you touch a hot stove, pain receptors in your skin fire signals forcing you to immediately pull your hand away from danger. Note that this movement occurs before you are ever conscious of the pain.
When you play a violin or guitar, as you become better at playing the instrument, you can play it without looking at the strings (remember the first time you tried, and you had to look at the neck of the guitar to play it). Without looking at your arm and fingers, you always know where they are anyway. For example, close your eyes and touch your nose, ear, and eye. You can complete routine and complex tasks, because of a proper working cutaneous system. Receptors found in your skin are the foundation of this system. Thermoreceptors give your skin the feeling of hot and cold, nociceptors allow you to feel pain, and mechanoreceptors respond to various pressures, vibrations and stretching of the skin. Your hypodermis. The epidermis is the outermost layer and is just layers of dead skin that are constantly being shed off and replaced. Two-point threshold/ Two-point discrimination It is the ability to discern those two nearby objects touching the skin are truly two distinct points, not one. It is often tested with two sharp points during a neurological examination and is assumed to reflect how finely innervated an area of skin is. In clinical settings, two-point discrimination is a widely used technique for assessing tactile perception. It relies on the

ability and/or willingness of the patient to subjectively report what they are feeling and should be completed with the patient’s eyes closed. A measure of tactile acuity defined as the smallest separation at which two points applied simultaneously to the skin can be clearly distinguished from a single point. It varies from 1 or 2 millimeters in the finger and tongue to more than 60 millimeters on the upper arm, upper thigh and back.

Review of literature:

Chang, B. P., & Lenzenweger (2001) examined 2-point discrimination performance in 1st- degree biological relatives ( n = 39) of individuals with schizophrenia and normal adult control participants ( n = 30) recruited from the community. An objective 2-point discrimination task was completed, adapted for use with a signal detection approach to permit separation of discriminability from response bias/criterion. Relatives revealed poorer performance on the index compared with controls. The 2 groups did not differ on suggesting a genuine difference in sensitivity but not response bias. The sensitivity deficit might reflect decreased spatial acuity and/or impaired intensity cue processing of tactile stimuli. Poor performance on the index was most closely associated with 2 schizotypic features, namely "odd beliefs/magical thinking." Fabbers, Bakkers et al (2008) examined the static and dynamic normative values for the two- point discrimination test and to examine its applicability and validity in patients with a polyneuropathy. Two-point discrimination threshold values were assessed in 427 healthy controls and 99 patients mildly affected by a polyneuropathy. The controls were divided into seven age groups ranging from 20–29, 30–39, up to 80 years and older; each group consisted of at least 30 men and 30 women. Two-point discrimination examination took place under standardised conditions on the index finger. Correlation studies were performed between the scores obtained and the values derived from the Weinstein Enhanced Sensory Test (WEST) and the arm grade of the Overall Disability Sum Score (ODSS) in the patients’ group (validity studies). Finally, the sensitivity to detect patients mildly affected by a polyneuropathy was evaluated for static and dynamic assessments. There was a significant age-dependent increase in the two-point discrimination values. No significant gender difference was found. The dynamic threshold values were lower than the static scores. The two-point discrimination values obtained correlated significantly with the arm grade of the ODSS (static values: r = 0.33, p = 0.04; dynamic values: r = 0.37, p = 0.02) and the scores of the WEST in patients (static values: r = 0.58, p = 0.0001; dynamic values: r = 0.55, p = 0.0002). The sensitivity for the static and dynamic threshold values was 28% and 33%, respectively. Foster and Bagust ( 2004 ) investigated differences in cutaneous 2-point discrimination and palpatory sensibility at different stages in a chiropractic training course and in field chiropractic practitioners. Static 2-point discrimination and palpation thresholds of the skin in the dominant index finger were measured in 102 subjects taken from the first and final years of a chiropractic degree/masters course and practicing field chiropractors. Two-point discrimination measurements were obtained by applying modified electronic engineering callipers mounted on a lever arm, which allowed the points to be lowered onto the skin at a constant rate and pressure. Palpation measurements were made by locating a nylon monofilament under a variable number of sheets of paper held in a purpose-designed frame. Differences in the 2-point discrimination and palpation threshold measurements

 Make sure subject do not get hurt with caliper.  Lighting should be well enough.  Subject must feel comfortable.  Eyes of the subject should be covered well.

Procedure:

 Before you start this experiment, be sure that you know how to use the calliper and how to open and close it. Practice touching your arm with it at different millimetre (mm) readings. It is important during the experiment that you touch your partner's skin with both tips at the same time; otherwise, they will easily be able to tell there are two points. Once you have the hang of it you are ready to begin!  Have your partner place the eye shades on and sit in a chair with a table in front of them. Then your partner places their arm on the table with their palm facing up. Now you take the callipers and start with your partner's fingertip.  Touch the callipers to their fingertip and ask them if they feel one point or two points. They should say one point, as the measurement is 0mm. Remove the callipers and increase the space by 2 mm. Reapply the callipers, be sure to touch both tips at the same time and ask again. If they still only feel one point, increase by another 2 mm, and reapply.  Continue^ this^ cycle^ until^ your^ partner^ feels^ two^ points.^ Record^ the^ millimetre measurement in the chart below.  For example, if your partner could tell that one point became two points^ at^ 6 mm on their fingertip, start the descending experiment at 10 mm. This ensures that your partner will feel two different points.  Do this test again for the top of one forearm.

Introspective Report:

This task was really very interesting, and I had lot of fun in doing this.

Observational Report:

The subject was very calm and confident during this experiment. She performed it well.

Result:

Trial Fingertip Forearm

Ascending 2mm 18mm

Descending 6mm 20mm

The aim of the experiment was to measure the two-point threshold of the subject. Two-point threshold pf the subject’s fingertip in ascending and descending was 2mm and 6mm, respectively. Whereas the two-point threshold of the subject’s forearm in ascending and descending order was 18mm and 22mm, respectively. Thus, it was found that two-point threshold of the subject was lower for fingertip then for the forearm. Therefore, hypothesis is proved.

Studies have shown that the mean two-point discrimination value obtained in our study, for the subjects aged 18 to 25 years is comparable to the normative value reported for a similar age group in other regions. Our study demonstrated increasing values of two-point discrimination threshold with increasing value.

Conclusion:

The subject supports the hypothesis as the two-point threshold of fingertip was lower than for the forearm in the both the ascending and descending order (2mm<18mm and 4mm<20mm)

Two-Point Threshold: Measuring the Sensitivity of the Somatosensory System, Cheat Sheet of Psychology

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Experiment 5:

Two-point threshold

Aim:

Introduction:

Review of literature:

Procedure:

Introspective Report:

Observational Report:

Result:

Trial Fingertip Forearm

Ascending 2mm 18mm

Descending 6mm 20mm

Conclusion:

References: