Abstract: The effects of task demands on spatial based IOR and color based repetition disadvantage effect were explored in 3 experiments. Twenty three undergraduate students participated in experiment 1 and the results showed significant color based repetition disadvantage effect whose measure is more than that in the simple detection task, when all the stimulus were presented on the same central location and the experiment task is color discrimination. Adding spatial uncertainty to the paradigm of experiment 1, experiment 2 and 3 separately asked 22 and 23 adult subjects to perform either discrimination or simple detection tasks. The results showed that there were both spatial based IOR and color based repetition disadvantage effect in the color discrimination tasks, however, there was no interaction between them, i.e., they acted independently. While there was only spatial based IOR in the simple detection tasks. Those results implied that which kind of repetition disadvantage effect will appear under some experimental situations and the measure of it are determined by the task requirements in experiments. Finally the authors discussed the present results with an inhibition model in the field of selective attention.

Key words: spatial based IOR, repetition disadvantage, task demands