A Biased View of Perceivers Commentary on Observer theory Bayes theory and psychophysics by B Bennett
The target chapter introduces the notion of an observer as an entity which applies a given Bayesian theory to the task of inferring world properties from sense data In fact most of this volume is concerned with observers in one form or another The basic idea is that the perceptual system uses a model of the current world context that is a domain theory to reduce the ambiguity inherent in the sense data and to select particular interpretations for the state of the world Example domain theories are the qualitative probabilistic models used for the motion of a ball in a box in Chapter the preference based scheme for the interpretation of handle shape and orientation discussed in Chapter the Bayesian models for shape from texture and shading used in Chapter and the cost function formulation proposed for the interpretation of shape illumination and pigmentation in Chapter In order to include such alternative forms of world models we use the term observer to refer loosely to any entity which applies a xed domain theory to the task of inferring world properties from sensory data Our bias is to view the perceptual system as a theorist in its own right not just an observer We claim that in order to understand perception we need to understand the way this theorist works that is how it selects a theory for a new domain how it applies a theory to choose particular interpretations for sense data how it compares di erent theories and how it revises and learns theories under the in uence of new information In contrast an observer is concerned with only one of these aspects namely how a xed theory is applied The distinction between theorist and observer is perhaps blurred by notions such as Yuille s competitive priors see Chapter or Each prior may lead to a single distinct Bayesian observer and the selection of one prior in favor of others can be thought of as a theory selection process Thus the overall system can be thought of as a theorist On