The Influence of Landmark Salience in a Navigation Task: An Additive Effect Between Its Components V. D. Chamizo and T. Rodrigo Universitat de Barcelona J. M. Peris and M. Grau Universitat Polite `cnica de Catalunya In 2 experiments, rats were trained in a Morris pool to find a hidden platform in the presence of 1 landmark. After acquisition, the rats were tested without the platform. Experiment 1 tested whether the size of a landmark and its relative distance from the platform are additive effects. On test, the rats’ best performance was with a near and big landmark; intermediate performance was with either a near and small landmark or a far and big one; and the worst performance was with a far and small landmark. The results of Experiment 2 suggested that the different distances from the goal of the 2 landmarks might not be sufficient to explain the previous results. Keywords: single landmark learning, landmark salience components, Morris pool, rats A growing body of evidence suggests that the spatial and temporal domains often share the same or similar conditions, basic effects, and mechanisms (for recent reviews of basic effects and Pavlovian phenomena in the spatial domain, see Chamizo, 2003; Rodrigo & Prados, 2003; and a whole monographic issue of the journal Psicolo ´gica, Mackintosh & Chamizo, 2002). Spatial block- ing and overshadowing are good demonstrations in favor of this claim. These effects, especially those obtained with strictly spatial tasks (e.g., for blocking and unblocking, see Rodrigo, Chamizo, McLaren, & Mackintosh, 1997, and Rodrigo, Arall, & Chamizo, 2005, respectively; for competition or overshadowing, see Sa ´nchez-Moreno, Rodrigo, Chamizo, & Mackintosh, 1999; Chamizo, Manteiga, Rodrigo, & Mackintosh, 2006) seem incon- sistent with O’Keefe and Nadel’s (1978) account of true spatial learning or locale learning. Their theory claims that this kind of learning is fundamentally different and develops with total inde- pendence from other ways of learning (like classical and instru- mental conditioning—taxon learning, according to these authors). Our aim in the present study was to investigate further parallelisms between the temporal and spatial domains. It has been shown (Artigas, Aznar-Casanova, & Chamizo, 2005; Chamizo & Rodrigo, 2004; Cheng, 1989; Cheng & Spetch, 2002; Cheng, Spetch, & Johnston, 1997; Rodrigo, Sansa, Baradad, & Chamizo, 2006; Spetch & Wilkie, 1994) that when spatial location is analyzed in a manner similar to what is normal with other properties or dimensions of the stimuli, such as wavelength and auditory frequency, the control exerted by the location of stimuli appears to be similar to that exerted by other properties or dimen- sions of the stimuli. For example, the effect of absolute temporal proximity of the conditioned stimulus (CS) to the unconditioned stimulus (US) in a Pavlovian preparation is well-known (Revusky, 1971). Normally, conditioning improves as the interval between CS and US decreases, although at very short intervals conditioning may be worse (Ost & Lauer, 1965; Schneiderman & Gormezano, 1964). In a parallel way, it has been found that the control acquired by a single landmark is different depending on its relative distance from or its absolute spatial proximity to a goal (Chamizo & Rodrigo, 2004; Cheng, 1989; Spetch & Wilkie, 1994). In the two experiments of the study by Chamizo and Rodrigo (2004), rats were trained in a Morris pool to find a hidden platform in the presence of a single landmark, which was inside a highly con- trolled enclosure. The distance between the landmark and the goal was varied in the two groups of each experiment. In Experiment 1, for one group, the position of the landmark was relatively close (50 cm) to the hidden platform (Group Near), whereas for a second group, it was exactly above the hidden platform (Group Above). During acquisition, rats in Group Above found the platform faster than rats in Group Near did. Subsequent test trials without the platform revealed spatial learning in both groups, but performance was better for Group Above. In Experiment 2, for one group, the position of the landmark was exactly the same as in Experiment 1 (Group Near), whereas for a second group (Group Far), it was relatively far away from the goal (110 cm). Rats in Group Near found the platform faster than rats in Group Far did. This result was also true in the test trials, which revealed a preference for searching in the correct quadrant of the pool in both groups, but this preference was significantly higher for Group Near. The implication of these results is that the control acquired by a single landmark is different depending on its relative distance from a hidden platform: Closer landmarks acquire better control than distant ones. These results show a clear parallelism in comparison with the effect of absolute temporal proximity of the CS to the US in classical conditioning (Revusky, 1971). Thus, both in the tem- poral and in the spatial domain, a conditioned stimulus (CS) or a landmark becomes more relevant, more salient, the closer it is to V. D. Chamizo and T. Rodrigo, Departament de Psicologia Ba `sica, Universitat de Barcelona, Barcelona, Spain; J. M. Peris and M. Grau, Departament de Matema `tica Aplicada II, Universitat Polite `cnica de Cata- lunya, Barcelona, Spain. This research was supported by Grant SEJ2004-07621 from the Spanish Ministerio de Educacio ´n y Ciencia to V. D. Chamizo. Correspondence concerning this article should be addressed to V. D. Chamizo, Universitat de Barcelona, Facultat de Psicologia, Departament de Psicologia Ba `sica, Passeig de la Vall d’Hebron, 171, 08035-Barcelona, Spain. E-mail: victoria.diez.chamizo@ub.edu Journal of Experimental Psychology: Copyright 2006 by the American Psychological Association Animal Behavior Processes 2006, Vol. 32, No. 3, 339 –344 0097-7403/06/$12.00 DOI: 10.1037/0097-7403.32.3.339 339