Normal Tactile Threshold

Normal Tactile Threshold

• The terms “normal threshold” and “classical threshold” identify the level of tactile input at which an individual’s senses react to stimulation. Below the threshold, there is no reaction; above the threshold, a reaction occurs. The reaction is effectively limitless but usually related to the sensation. The subject may, for instance, learn something, become stimulated, notice the environment has become warmer or jump away from a threat.

Injury

• Experiments have shown that a deficit in tactile response -- effectively a lowering of the tactile threshold and a reduction in the ability to learn -- is directly related to parietotemporal lesions: damage to those parts of the brain that process sensory input. Tactile sensations experienced on the side of the body opposite the side of the brain where the damage occurred will continue unaffected. On the side of the body where the injury occurred, the tactile threshold remains impaired. Other experiments have demonstrated that chronic, non-specific low back pain has the same effect; the ability to learn through tactile experience is diminished. A joint experiment between the School of Health Sciences at the University of Notre Dame in Fremantle, Australia and the School of Health Sciences and Social Care at Brunel University in the U.K. found “a significant difference” between control subjects -- individuals with no back pain -- and back-pain patients. In patients with back pain, the normal tactile threshold was impaired.

Vibro-Tactile Thresholds

• Experiments have been carried out that prove human awareness on the tactile level can be increased by the addition of sounds to the environment. Tactile information that is sub-threshold in a silent environment is detectable when noise is added. This is called a “psycho-physical phenomena,” meaning that the activity of the brain is affected by external stimuli of which it is consciously unaware. Because sound is, in fact, vibration, the use of noise to increase the tactile threshold is called a vibro-tactile effect. One such experiment reported by BioMed Central noted that “According to the classical threshold assumptions, a correct second choice response corresponds to a guess attempt with a statistical frequency of 50 percent.” Their results found that when a sound was present, the correct reactions rose to 67 percent.

Recent Evolution

• The term “tactile sense” has come to have a different meaning since the advent of the near-ubiquitous keyboard in everyday life. In the context of using telephones, computers, i-readers and the like, tactile sense refers to the human-machine interface.