Tactile diplopia (diplesthesia) on the human fingers

Area of Science:

• Neuroscience
• Somatosensory system
• Human perception

Background:

• The somatosensory system processes tactile information, but its mechanisms for distinguishing single from multiple stimuli under altered conditions are not fully understood.
• The crossed-finger illusion, where touching two adjacent fingers together leads to perceiving a single stimulus as two, provides a model for exploring tactile perception anomalies.

Purpose of the Study:

• To investigate the effect of skin displacement between fingertips on the perception of a single tactile stimulus.
• To quantify the probability of tactile diplopia (perceiving one stimulus as two) as a function of skin displacement.

Main Methods:

• Five subjects had their third and fourth fingertips pressed together to create varying degrees of skin displacement.
• A single spherical stimulus was applied simultaneously to both displaced fingertips.
• Subjects reported their perception of the stimulus (single or double).

Main Results:

• The probability of detecting a single stimulus at rest was high (0.90).
• This detection probability decreased significantly with increasing skin displacement.
• At maximum displacement, the detection probability dropped to 0.04, indicating a 0.96 probability of perceiving the single stimulus as double (tactile diplopia).

Conclusions:

• Skin displacement between fingertips induces a tactile diplopia phenomenon, analogous to Aristotle's crossed-finger illusion.
• This finding demonstrates a diplopia-like effect within the somesthetic system.
• Tactile diplopia offers a novel avenue for studying the complexities of tactile perception and sensory integration.