A study of spatial parameters encoded during exploration in hamsters.

Abstract

Centre National de la Recherche Scientifique, Marseille, FranceIn two experiments the exploratory reactions of hamsters to various rearrangements of familiarobjects were examined. During two sessions, the subjects were allowed to explore a circular, openfield containing four different objects. During a third test session, one or several objects were dis-placed, changing the shape and/or the size of the area denned by the object set. Significant reexplora-tion was found when the change brought about during the test session affected the geometrical re-lations between the objects or when an object was removed. In contrast, changes that did not modifythe geometrical configuration of the arrangement of the objects, but only modified the distanceof one object to another, did not elicit any reexploration. Additionally, it was found that selectivereexploration of the actually displaced objects occurred only when the change removed this object acertain distance from the others. These results are discussed in terms of complexity andmore generally with regard to the spatial parameters that are selected, processed, and stored duringexploration.Exploratory reactions to novelty are a consistent behavior inmost mammals. This behavior can take several forms: arrest orstartle reactions, orienting reactions, scanning head move-ments, rearing, locomotion, sniffing, and so forth. In addition tothe exploration of distal features, close investigation by contactwith novel elements of a situation is likely to be displayed bymacrosmatic species such as rodents. These contacts are a reli-able and easily observable index of exploration. One character-istic of exploratory reactions is their consistent and progressivedecrease over time (habituation).Many studies have shown that through exploratory activity,animals acquire some knowledge about the characteristics ofthe objects with which they are confronted. Berlyne (1960), forexample, has demonstrated that if one of three familiar objectsis replaced by a novel one, rats investigate the latter significantlymore than the two unchanged ones. By using a variety of differ-ent procedures, similar results have been found in gerbils(Cheal, 1978), marmosets (Menzel & Menzel, 1979), and ba-boons (Joubert & Vauclair, 1986).Changing the location or the locations of familiar object thathave been set up in an open field also elicits renewed investiga-tory responses to the displaced object(s) in rats (Gorman S Wilz & Bolton, 1971).These data, and others obtained from gerbils by using a differentprocedure (Thinus-Blanc & Ingle, 1985), show that during ex-ploration, animals also spontaneously process some spatialcharacteristics of the situation.This research was supported by the Centre National de la RechercheScientifique and by the Ministere de la Recherche et de la Technologic(Grant 85C 1336).The authors wish to acknowledge the contribution of anonymous re-viewers who made a number of helpful comments and suggestions on aprevious version of the article.Correspondence concerning this article should be addressed to C.Thinus-Blanc, Centre National de la Recherche Scientifique, Labora-toir e de Neurosciences Fonctionnelles (Ulbis), 31 chemin Joseph-Aigu-ier, 13402 Marseille cedex 9, France.In a recent study using the stimulus elicited investigationparadigm (Cheal, 1978), Poucet, Chapuis, Durup, and Thi-nus-Blanc (1986) investigated the nature of the spatial relationsperceived by hamsters during exploratory activity. Severalgroups were habituated to a spatial arrangement of four objects.After this, each group was exposed to a modified spatial con-figuration of these objects during a single test session. Thechange in the spatial arrangement affected either the topologicalrelations among the objects, the overall shape formed by theobject set, or both. Each kind of change induced renewal of ex-ploration. When topological relations or the overall shape wereseparately modified, reexploration was selectively directed to-ward the displaced object(s). When the change affected both lev-els of spatial organization, reexploration was generalized to allth e objects , even th nondisplaced ones as if rearrangementwere perceived as n entirely new situation.The general principle of the present study follows that of theaforementioned experiment (Poucet et al., 1986): The effects ofdiscrete changes in the configuration of objects contained inan open field were studied with the assumption that a changeeliciting a renewal of exploration reflects a detection of thatchange by the animals. The only means for the subjects to detectsuch a change is by comparison with an internal representationof the initial situation. If the modification, although perceptu-ally detectable by the animals, does not elicit any increase inexploratory activity, it can be reasonably concluded that themodality of the situation affected by the modification had notbeen encoded in the internal representation. Moreover, com-parisons of renewed exploratory reactions directed toward dis-place d an nondisplace objects woul provide further infor-mation about the reference systems that are (or are not) consti-tutive elements of the representation.In the present experiments, we investigated the effects ofchanges affecting only the distances between objects withoutaffecting the topological relations between them. In the Poucetet al.'s experiment, only one group of hamsters was subjected toa chang that involved th metrical relation s of objects. Thichange induced a selective reexploration of the displaced object.