I think it's also important to note that when looking at a blank screen there is nothing stimulating, and stimulation (external or internal) drives our attentio

I think it's also important to note that when looking at a blank screen there is nothing stimulating, and stimulation (external or internal) drives our attention control. Putting a progress indicator on something gives us something to pay attention to, and so we're more likely to respond with frustration than inattention.