Absence of overshadowing and blocking between landmarks and the geometric cues provided by the shape of a test arena Andrew Hayward, Anthony McGregor, Mark A. Good, and John M. Pearce Cardiff University, Cardiff, UK In three experiments rats were required to escape from a pool of water by swimming to a sub- merged platform. The position of the platform was determined by the shape of the pool, which was either rectangular or triangular. A landmark that was located on the surface of the pool near the platform failed to overshadow (Experiment 1) or block (Experiment 2) learning about the position of the platform with reference to the shape of the pool. Experiment 3 revealed a similar outcome with cues outside the pool, which could be used, in addition to the shape of the pool, to identify the location of the platform. These findings imply that theories of learning that assume that stimuli must compete with each other for the control that they acquire may not apply to spatial learning based on the shape of the environment. Demonstrations of blocking and overshadowing are regarded as important for at least two reasons. First, they indicate that stimuli are in competition with each other for the control that they acquire over behaviour, and, as such, these effects support theories of learning that incor- porate an error correction principle (e.g., Pearce, 1994; Rescorla & Wagner, 1972). According to this principle, learning about a stimulus will cease when the outcome it signals is accurately predicted by the stimulus itself together with the stimuli that accompany it. Second, demon- strations of overshadowing and blocking in a variety of settings have been taken as evidence for the generality of the laws of learning. Hence, as Mackintosh (1974) points out, the claim that taste aversion conditioning is different to conditioning with exteroceptive stimuli was called into question when it was found that both blocking and overshadowing could be demonstrated with flavours that were paired with illness (Revusky, 1971). Experiments showing cue competition effects in spatial tasks have likewise led to a growing acceptance that spatial learning is governed by the same theoretical principles that operate in Requests for reprints should be sent to John M. Pearce, School of Psychology, Cardiff University, Cardiff CF1 3YG, UK. Email: pearcejm@cardiff.ac.uk This research was supported by the UK Biotechnology and Biological Sciences Research Council and by the UK Medical Research Council. We are grateful to Peter Jones for his assistance with Experiment 3, and to Victoria Chamizo for her suggestions concerning the interpretation of the results.  2003 The Experimental Psychology Society http://www.tandf.co.uk/journals/pp/02724995.html DOI:10.1080/02724990244000214 THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2003, 56B (1), 114–126 Q0667—QJEP(B)SI B9/Jan 13, 03 (Mon)/ [13 pages – 0 Tables – 3 Figures – 0 Footnotes – 0 Appendices]. . Centre single caption. shortcut keys. READ AS KEYED