Pattern-Matching and Invariance

In neuroscience, the process I call pattern-matching is often called invariance.

Yohan John in Quora raises the question and suggests the form of the answer: How does your brain discover similarity in the midst of so much dissimilarity? The answer is that the brain somehow creates invariant representations of objects and patterns.

What is invariance?

In math and physics, an invariant is a property of a system which remains unchanged under some transformation. Here’s three short ways the invariant concept is used in neuroscience.

  • Sensory invariance. We can identify an object no matter its physical position with respect to us. A table seen from five feet straight on and from twenty feet away at an angle are recognized as the same table.
  • Partial information. A quick glimpse of a face across a crowded dance floor can be enough to identify your friend.
  • Contradictory information. Your friend meets you, but surprise – has no hair. Nonetheless, you recognize your friend, despite never having seen this look before.

Two Neural Properties

A narrow, but vital thread to that answer arises from two properties of the neuron—the neural threshold and the All-or-None Principle.

James Kalat combines both in this statement from his text, Biological Psychology.

Any subthreshold stimulation produces a small response proportional to the amount of current. Any stimulation beyond the threshold, regardless of how far beyond, produces the same response

Together the properties imply that closely similar neural inputs are treated as if they are identical.

Almost Gate

I call this neural feature the Almost Gate. If two inputs are almost the same, downstream they are the same.*

The two inputs can be separate concepts, one originating from current sensory information and the other pulled from memory of a resembling, past situation.

Seawall with waves crashing against it

If the neuron’s electrical potential exceeds the threshold, it doesn’t matter how much it exceeds it, it goes over the Almost Gate.

*Pro and Con of the Almosst Gaate

  • The Almost Gate allows (guarantees), that, at times, we make mistakes like jumping to conclusions.
  • Yet when a person has a relatively low Almost Gate, creativity abounds.

Seawall photo: www.davis.abwe.org/image/detail/155516.jpg

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