I'm currently reading "Perceived Order in Different Sense Modalities" (Hirsh and Sherrick, 1961). In they repeatedly use the abbreviation "O" and I have no idea what it stands for. It seemed to have been in common use back in those days, but fallen out of favor since. Some usage examples:
- To investigate the limits of the ability to distinguish successive from simulateneous events, we need only a pair or series of events about which we can ask O whether there were one or two [...].
- The question for Exp. I was: how much time must intervene between two visual stimuli for O to report correctly the order in which they occur?
- Four trained Os, between 18 and 30 yr. old, were tested singly.
Obviously, O means something along the line of "subject" or "participant". However, I'm wondering what it stands for exactly. My best guess would be something like "observer".