Object novelty recognition is derived from the spontaneous preference demonstrated towards an object which has not been encountered in the past. This preference of a novel object is the result of the retrieval of stored representations from previous experience of other objects. The stored representation of an object may be constituted from the whole or limited encoded features; it may also comprise the context or some elements of the context in which the object was presented. In rodents, object novelty recognition has been mostly concerned with memory types and processes, and it is only recently that a limited number of research studies started looking at object perception and encoding processes. In this chapter, we will describe the evidence from animal and human literature regarding the object features, the complexity objects, and the similarity between the paired objects and the representation of the familiar object. We will also describe various factors that contribute to encoding and discrimination or recognition of objects. Among these factors are the amount of pretest habituation sessions, changes in locomotor activity and exploration, and changes that may occur from the use of single versus a pair of identical or different objects in the acquisition phase. As discussed in this chapter, the object novelty recognition test has its limitations, particularly regarding the study of object features and working memory which require strict control over the test parameters. This could be resolved with the development of automated visual object recognition tests, which takes into consideration rodents' visual abilities and the consequences of these in the design of a discrimination and a delayed nonmatching-to-sample test apparatus.
