maze-bright and maze-dull rats
two groups of rats that were separated based on their performance in a standardized maze problem. Those that performed best were bred with each other, as were those that performed most poorly. Over relatively few generations, there was a complete separation in performance, with none of the maze-bright rats overlapping in scores with maze-dull rats. However, the selective breeding appeared to be specific to the maze tests that were used and did not affect learning ability more generally; moreover, maze-dull rats reared in an enriched environment (see enrichment) could perform as well as maze-bright rats.