Learning in combined-feature search: specificity to orientation.

We investigated the dynamics and specificity of learning in the search for a target defined by combined features belonging to the same dimension (a rotated L) among homogeneous or heterogeneous distractors (differently rotated Ls). We found that learning makes searching faster although the search strategy does not change, remaining parallel with homogeneous distractors and serial with heterogeneous distractors. Learning was found to be specific for combined-feature orientation, although simple features did not change in the transfer stimulus: Transfer was partial when either the target or the distractors were rotated (so that their global orientation became the same) and totally absent when target and distractors were swapped. These results, which apply to searches among both homogeneous and heterogeneous distractors, rule out the possibility that learning is specific for orientation of just simple features. Instead, the results suggest that specificity of learning with combined features reflects the activation of junction detectors responding to a combined feature of a particular orientation.