Aging and Two Point Touch

When we hear “two-point touch,” our initial thought is likely an object touching ourselves or another object at two separate points of interest. Frankly, that’s exactly what it is. The two-point touch technique measures the smallest distance between two points at which an individual can perceive two distinct stimuli (Oxford Reference, 2020). Our ability to differentiate between these two distinct points is called spatial acuity. The smaller the distance that we can detect two separate points with the two-point touch technique, the higher our spatial acuity. You can test spatial acuity using the two-point touch technique with a partner. Start by creating a two-point discrimination tool, such as a caliper or a bent paper clip. Have your partner close their eyes. Then touch them with the two points of the greatest distance. Common areas to test are the forehead, arm, back, leg, hand, and foot. Ask if they felt one or two points touching them. If they detect two points, repeat the process with a smaller distance. The lower their two-point threshold, the less distance it will take for them to detect two distinct points. Try testing the two-point threshold on people older and/or younger than you to see the differences in spatial acuity.

However, there are disadvantages to two-point touch. A study suggested that the two-point touch does not have good test-retest reliability, which is the consistency of results between different times of measurement in the same test conditions (Bruns et al., 2014). The study also pointed out that two-point touch yields results that could be inconsistent with measurements done by other validated measurement methods, suggesting that the two-point touch alone does not serve as an efficient way of wholly measuring spatial acuity. Another criticism aimed at how the two-point touch is inconsistent and leads to variations of results between participants that researchers could not explain (Lundborg & Rosen, 2004). Even the fact that the test relies on how patients can differentiate two points from one is doubted; some studies demonstrated how the test ​allows for much better performance for small distances of the two-point touch (Tong et al., 2013).

Spatial acuity within our fingertips typically declines with age (Martin et al., 2018). Some leading factors for this deterioration include a decrease in blood flow to nerve endings, lack of proper nutrients, issues related to the brain, nerve damage, and chronic diseases (Martin et al., 2018). With less spatial acuity, elders may also have difficulty recognizing different temperatures, pressure, vibration, as well as when they are in pain (Martin et al., 2018). When reading that, you may think, “that might not be so bad,” because they wouldn’t need to worry about feeling a hot pan or having their fingers go numb on a cold winter day. However, this lack of sensitivity leads to the elderly population being at a much greater risk for frostbite, hypothermia, burns, injuries, etc. (Martin et al., 2018).

Though the concept of two-point touch is known to decline with age, many people are unaware that there are changes seen in childhood as well. Research shows that fingertip size has a significant influence on spatial acuity: larger fingertips have poorer spatial acuity because the mechanoreceptors are likely more dispersed (Peters & Goldreich, 2013). That being said, it makes sense that our spatial acuity may decline as our hands and fingertips grow from childhood, though age doesn’t seem to have a significant effect when the topic of interest is only children. More specifically, even though our fingertips may increase in size as we age, resulting in a decline of spatial acuity, our ability to process information in the central nervous system (CNS) is likely to improve with age (Peters & Goldreich, 2013). Therefore, older ages do not necessarily always lead to lower spatial acuity (Peters & Goldreich, 2013).

Researchers took the known ideas of neurological pathways and sensation and looked into how aging affects the sensation of touch. They ran a study on a group of young and elderly participants to test how touch changes over time. What we have already established in this post is that spatial acuity is said to significantly deteriorate with age (Wichremaratchi & Llewelyn, 2006). What is interesting about this article, is that with deteriorating spatial acuity, there is also a correlation with speech articulation, handgrip, and postural stability (Wichremaratchi & Llewelyn, 2006). It is the diminished spatial acuity in the lips that account for the speech articulation, the deteriorating spatial acuity in the fingers and palm that account for handgrip, and the worsened spatial acuity in the foot that link to the poor posture (Wichremaratchi & Llewelyn, 2006). It is interesting to note these relationships because spatial acuity clearly does not deteriorate alone, rather many other functions diminish as well.

Despite the inconsistencies with the two-point touch method, it remains a commonly used method to test spatial acuity. As our sense of touch decreases over time as we age, the two-point touch method is a way to measure this decrease in spatial acuity at home. It’s important to be aware of how our spatial acuity works so that as our ability to distinguish between two points diminishes, we can understand our loss of sensitivity.

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