Information processing with population codes

Abstract

Information is encoded in the brain by populations or clusters of cells, rather than by single cells. This encoding strategy is known as population coding. Here we review the standard use of population codes for encoding and decoding information, and consider how population codes can be used to support neural computations such as noise removal and nonlinear mapping. More radical ideas about how population codes may directly represent information about stimulus uncertainty are also discussed.

Motion detection, noise reduction, texture suppression, and contour enhancement by spatiotemporal Gabor filters with surround inhibition

“…This ambiguity of the separate filters regarding the presence or absence of motion in a given position is in contrast with the sharp distinction that our visual system can make between the two conditions. Evidently, the presence or absence of motion at a given position is coded in the set of responses of multiple filters at that position, a situation that is referred to as population coding (Pouget et al 2000). We show that motion at a given spatial position can be detected in a straightforward way from the motion energy population code responsible for that position.…”

Learning and inference in the brain

“…the orientation of a contour). Pouget, Dayan, and Zemel (2003) explore the more recent suggestion "that neural computation is akin to a Bayesian inference process, with population activity patterns representing uncertainty about stimuli in the form of probability distributions (e.g., the probability density function over the orientation of a contour)." Does the brain estimate or infer?…”

Computational approaches to motor control

“…In a population code, information about a variable is represented by the pattern of activity in a large number of cells [9]. The direction of arm movement during reaching is coded by neurons whose firing rate varies as the cosine of the angle between a cell's preferred direction -where it is maximally active and the actual movement direction.…”