Categorization is ‘baked’ into the brain

I've been meaning to point out this Nature Reviews Neuroscience Perspectives article by Barrett and Miller (the same Miller referenced in the previous post).  I pass on just the abstract and initial paragraphs of their model. The article has some very striking graphics, and motivated readers can request a copy of the article from me.  (It is important to point out that the choice of the limbic core as the analytic starting point is somewhat arbitrary, rather than being derived from basic data itself.)

Abstract

Categorization, the grouping of objects, living organisms, actions or events into equivalence clusters, is fundamental to adaptive behaviour. Traditionally, it is assumed that categorization begins with feature detection and ends with assigning representations stored in memory. Here we review converging evidence from neuroanatomy, electrophysiology, brain imaging and cognitive science to suggest an alternative view: categorization is not the end stage of perception but occurs throughout signal processing, from the very beginning. It is a core computational strategy of the brain, implemented through a neural context created by predictive feedback signals that organize feedforward processing. 

Introduction

A category is a group of objects, living organisms, actions or events that are similar enough to be treated as equivalent for some purpose or function. Categorization, the process of treating something as equivalent to something else, is fundamental to life. The ability to determine ‘this is like that’ allows animals to draw on past experiences to guide present actions. All animals categorize, generalizing from past experiences at temporal and spatial scales relevant to their biology and ecological niche. Categorization reduces metabolic costs by minimizing uncertainty in a constantly changing, partially predictable world.

In this Perspective, we discuss the possibility that categorization is not the pinnacle of brain processing, as is traditionally assumed. Instead, categorization is a fundamental operating principle that describes the functional consequences of signal processing throughout the brain. We integrate evidence from neuroanatomy, electrophysiology, brain imaging and cognitive science to suggest that category construction begins as patterns of predictive feedback signals for abstract motor plans. Feedback signals create a neural context that actively shapes the processing of feedforward sensory signals, organizing the reduction of their dimensionality to serve situated, functional goals. In this view, the brain categorizes sensory signals from the outset, rather than as a final-stage process following sensation, attention and perception.

We begin with a review of the main cytoarchitectural gradient that reduces the dimensionality of feedforward sensory inputs to the cerebral cortex. We then discuss the seemingly counterintuitive idea that reverse signal flow along this gradient expands dimensionality to generate prediction signals that shape the processing of and ultimately categorize those inputs to give them meaning. This universal continuous category construction starts at the limbic core of the brain, in areas that are at the core of the brain’s regulation of the body, and supports metabolic efficiency by anticipating and preparing for energy needs before they arise, a condition known as allostasis. In this way, continuous category construction and the resulting categorization satisfy a key biological constraint, energy optimization, which is an organizing principle of life and evolution