diameter. These can be taken as indicators of differing imagery performance in the various tasks. Fig. 4
shows an overview of the effect sizes of the factor diameter for the different age groups and the different
tasks in Experiments 1 through 3 (the ‘‘blind tilting” task is reported below). The more or less
horizontal lines for the manual tilting task and the judgment task show that there were no significant
age trends in these two tasks. Whereas no age group considered the factor diameter in the judgment
task, the effects for diameter in the manual tilting task were far beyond the significance level of .05.
The ascending graph for the remote control task shows a clear age trend for effects sizes of diameter.
Thus, younger children discriminated the diameters less when they turned the glasses by means of a
motor instead of their own hands. For 5-year-olds, the effect of diameter did not reach the significance
level of .05, but also 7-year-olds showed smaller effects compared with the two older age groups and
compared with the task where they turned the glasses manually. For 9-year-olds and adults, the glass
diameter had large effects even without motor feedback.