Understanding perception starts with the five senses — touch, taste, smell, hearing and sight — and it’s deceptively simple. While it’s easy enough to understand how each operates in isolation, scientists are still finding connections that push the boundaries of our understanding. Consider taste: While the smell/taste team-up is well known, recent studies suggest that proteins used for sight may also play a role in food selection.
Now, scientists from New York University (NYU) have uncovered a new connection between human sight and our sense of touch — under the right conditions, involuntary eye movements go missing to improve tactile predictability.
According to the Nature-published study — Oculomoter freezing reflects tactile temporal expectation and aids tactile perception — there’s a link between predictable tactile events and the behavior of human eyes, and it all starts with microsaccades.
Here’s how it works. Even when we’re focused on something — like a good book or compelling conversation partner — our eyes wander. Larger movements that rapidly shift our field of focus are known as saccades, and may be either voluntary or involuntary. Microsaccades are much smaller and typically go unnoticed; even when we think we’re completely focused on a task, our eyes never stop moving. How small are these mini-movements? According to Science Direct, “Microsaccades are very small saccades with amplitudes typically less than 0.1 degree of visual angle, and are interspersed with slow drifts.”
It turns out, however, that under certain conditions these microsaccades take break from their constant eye endeavors to help us focus on something else: tactile sensation.
The Temporal Tap Trap
To further explore the sight/touch connection, lead author and professor of psychology and neural science at NYU Marisa Carrasco and her team designed an experiment that combined physical stimuli and temporal cues to test participants’ tactile predictive ability.
Using a small, finger-attached device that produced either slow (low frequency) or fast (high frequency) vibrations, participants were asked to identify which type of vibration they felt as quickly as possible after it occurred. The arrival of these vibrations was always announced by a small “tap” from the device, but the interval of time between the initial tap and follow-up vibration varied between participant groups. In some cases the time between tap and tremor was uncertain, while in others it was precisely regulated. Not surprisingly, more consistent connection between tap and time made it easier for study subjects to predict when vibrations would occur and what form they would take.
But the team also found an interesting eye outcome: the suppression of microsaccades.
By having participants stare at a “fixation point” displayed on a computer screen during the experiment, the NYU researchers were able to measure the frequency of their microsaccades. Comparisons of these rapid movement rates between groups with fixed and variable time/tap intervals revealed that when subjects could accurately predict the timing of the vibration, microsaccade rates would significantly decrease just before the vibration occurred. In addition, this microsaccade suppression improved participant ability to distinguish between slow and fast stimuli.
According to Stephanie Badde, first author of the paper and NYU post-doctoral researcher, “This connection between the eyes and touch reveals a surprising link across perception, cognition, and action.” While more work is needed to fully understand this eye/touch teamwork, the NYU study results suggest a perceptive benefit to switching off microsaccades when the human body anticipates a tactile stimuli, in effect enhancing our sense of touch to both prepare for the upcoming sensation and quickly capture data about its behavior.
Sense and Sensitivity
Understanding perception helps expand the sum of human knowledge. Learning more about how we sense — and how sensitive we are to specific stimuli — gives scientists a clearer picture of how humans evolved and how we’re continuing to change. Consider the innately human quality of creativity. While some senses — such as sight for artists and hearing for musicians — may represent the primary medium of making, perhaps cooperation and coordination across differing perceptive paradigms is the secret to our continuing creative success.
Put simply? The eyes have it — and they know when to stop it to help enhance human tactile perception of potentially predictable events.
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