Perceptual Learning via Modification of Cortical Top-Down Signals

Roland Schäfer,Walter Senn,Eleni Vasilaki

doi:10.1371/journal.pcbi.0030165

Abstract

The primary visual cortex (V1) is pre-wired to facilitate the extraction of behaviorally important visual features. Collinear edge detectors in V1, for instance, mutually enhance each other to improve the perception of lines against a noisy background. The same pre-wiring that facilitates line extraction, however, is detrimental when subjects have to discriminate the brightness of different line segments. How is it possible to improve in one task by unsupervised practicing, without getting worse in the other task? The classical view of perceptual learning is that practicing modulates the feedforward input stream through synaptic modifications onto or within V1. However, any rewiring of V1 would deteriorate other perceptual abilities different from the trained one. We propose a general neuronal model showing that perceptual learning can modulate top-down input to V1 in a task-specific way while feedforward and lateral pathways remain intact. Consistent with biological data, the model explains how context-dependent brightness discrimination is improved by a top-down recruitment of recurrent inhibition and a top-down induced increase of the neuronal gain within V1. Both the top-down modulation of inhibition and of neuronal gain are suggested to be universal features of cortical microcircuits which enable perceptual learning.

Highlights

Since Plato’s Allegory of the Cave (360 BC) and Kant’s Critique of Pure Reason (1787), it is often suggested that our perception of objects in the outer world can never tell us what they really are. ‘‘If men had green glasses in place of their eyes, they would perceive the objects as green, and never be able to tell whether this color was intrinsic to the objects or just of our perception’’
We show in a model that top-down modulation of primary visual cortex (V1) during unsupervised perceptual learning can suppress intrinsic nonlinearities in V1
Modifying the stimulus representation within the early sensory cortex may lead to an improvement on one discrimination task, but may have long-lasting negative effects on another task

Summary

Introduction

Since Plato’s Allegory of the Cave (360 BC) and Kant’s Critique of Pure Reason (1787), it is often suggested that our perception of objects in the outer world can never tell us what they really are. ‘‘If men had green glasses in place of their eyes, they would perceive the objects as green, and never be able to tell whether this color was intrinsic to the objects or just of our perception’’ (letter of Heinrich von Kleist to his fiancee Wilhelmine von Zengen, 22 March 1801, in which he describes Kant’s ideas, http://www.kleist.org [in German]). Since Plato’s Allegory of the Cave (360 BC) and Kant’s Critique of Pure Reason (1787), it is often suggested that our perception of objects in the outer world can never tell us what they really are. Collinear edges are enhanced by the intrinsic V1 circuitry [1], and our brightness perception will never match the physical luminance. Perceptual training without teacher feedback may still improve our brightness discrimination abilities [1], casting certain doubts about the strict empirical view. How is it possible to reach more veridical perceptions by just ‘‘pure reason,’’ i.e., by intrinsically adapting the cortical dynamics without being told about the mismatch between percept and true physical quality?

Methods

Results

Discussion

Conclusion