Violation of pure insertion during mental rotation is independent of stimulus type, task, and subjects' age

The experiment validated and extended the finding of Ilan and Miller (1994) [A violation of pure insertion: mental rotation and choice reaction time. Journal of Experimental Psychology: Human Perception and Psychophysics 20, 520-536] that the mental rotation process is not purely inserted into a mirror-normal discrimination task. In contrast to their work we used other experimental stimuli (drawings of animals instead of characters), a different task (same/different comparison) and investigated this effect under a developmental perspective. Adults and children between the age of 8 and 10 took significantly longer to respond to upright drawings of animals in conditions containing rotated stimuli than in conditions containing only upright stimuli, indicating a violation of pure insertion. In general, we found evidence that the violation of pure insertion during a mental rotation task itself can be generalised across stimulus type, task, and subject populations. However, for children this effect was independent of the format of the stimuli, while for adults the effect was larger for mirror-imaged than for identical objects. This suggests that the violation of pure insertion might occur at different processing stages as a function of age.