The Espinet and the perceptual learning effects in flavour aversion conditioning: Do they depend on a common inhibitory mechanism? Antonio A. Artigas and Joan Sansa Universitat de Barcelona, Barcelona, Spain Jose ´ Prados University of Leicester, Leicester, UK In three experiments rats were given short or long preexposure (4 or 10 sessions) to two compound flavours, AX and BX, according to an intermixed or a blocked schedule. Following preexposure, aversion conditioning trials were given with AX as the conditioned stimulus (CS). In Experiments 1 and 2, retardation and summation tests were then carried out to assess the inhibitory properties of B (an Espinet procedure). In Experiment 3, test trials evaluated generalization from AX to BX (the standard perceptual learning procedure). The results showed that B performed as an inhibitor of the unconditioned stimulus (US; an Espinet effect) only after long intermixed preexposure, whereas a reliable perceptual learning effect was observed both after short and after long preeexposure. The observation that B had no detectable inhibitory properties after short preexposure casts doubt on the suggestion that inhibitory learning is responsible for perceptual learning after brief exposure to AX and BX. A conditioned aversion acquired to one con- ditioned stimulus (CS) will generalize to a novel stimulus to the extent that they share some common elements. However, it is well established that previous experience with stimuli can reduce generalization between them—that is to say, it can increase their discriminability. One factor that is known to modulate changes in discrimin- ability is the schedule according to which the to-be-discriminated stimuli are presented. If the stimuli are presented during preexposure accord- ing to an intermixed schedule, subsequent discrimination between them will be easier than if they are presented according to a blocked schedule (e.g., Bennett, Scahill, Griffiths, & Mackintosh, 1999; Dwyer, Hodder, & Honey, 2004; Honey, Bateson, & Horn, 1994; Mondrago ´n & Hall, 2002; Prados, Hall, & Leonard, 2004; Symonds & Hall, 1995). In the study by Symonds and Hall (1995), for example, rats given intermixed preexposure to two com- pound flavours AX and BX (e.g., AX, BX, AX BX, ...) showed better subsequent discrimination between them than control rats that were given Correspondence should be addressed to A.A. Artigas, Departament de Psicologia Ba `sica, Universitat de Barcelona, Pg. Vall d’Hebron, 171, 08035–Barcelona, Spain; or to J. Prados, School of Psychology, University of Leicester, University Road, Leicester LE1 7RH, UK. Email: talvarez@ub.edu or jpg19@le.ac.uk We are indebted to Nuria Vicente for her help on writing the present paper and to G. Hall for useful comments. This research was supported by a grant from the Spanish Ministerio de Ciencia y Tecnologi ´ a (BSO2001-3503) to the authors. # 2006 The Experimental Psychology Society 471 http://www.psypress.com/qjep DOI:10.1080/02724990544000022 THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY 2006, 59 (3), 471–481