Category-specific effects in object identification: what is "normal"?

Previous research on category-specific effects in subjects with intact brains, have found a disadvantage for the identification of natural objects compared to artefacts. This has been taken to support the explanation that natural object deficits in brain-damaged subjects are nothing more than an exaggeration of a "normal" tendency. More recent investigations have, however, uncovered the opposite normal tendency, an advantage for natural objects (Gerlach, 2001; Laws and Neve, 1999). The present study investigated the possible causes of this discrepancy. Three experiments revealed category-specific disadvantages for natural objects in normal subjects despite using stimulus materials rigorously balanced for a) concept familiarity, b) visual complexity, c) name frequency and d) name length. Furthermore, it was found that the very same set of stimulus materials could lead to natural object advantages as well as natural object disadvantages, depending on whether trials in a matching paradigm were positive or negative. In a naming paradigm, there was no natural object disadvantage when stimulus presentation durations were short. The discrepancy present in the literature can be solved by an account emphasising perceptual strategies instead of invoking a lack of adequate experimental control in the previous studies.