Your article is very well written and has been helpful to me. I do, however, ask that you consider alternative interpretations in a few matters, discussed below.
"Why it matters that the critical stimulus is unexpected":
You write that the stimulus must be unexpected so as to rule out insufficient attention and thus implicate inattention. (e.g., "[the stimulus] might be attended, just not sufficiently to produce awareness of it. Such failures of awareness might be due to insufficient attention rather than inattention.") However, an unexpected stimulus might not be completely unattended. It seems that, for all we know, the gorilla in Simons and Chabris (1999) drew some attention but not enough "to produce awareness of it." Is there evidence to support your position, other than an assumption that unexpected stimuli are completely unattended? After all, unexpected stimuli are often apt to draw attention precisely because they are unexpected.
DS -- Everything but the last sentence in your comment above is right. You're right that we can't guarantee that the gorilla, for example, was entirely unattended. The question is whether people voluntarily direct attention to it. If it's unexpected, they can't do that until they've detected it. If it's not unexpected (meaning they know it will be there at least some of the time), then they are more likely to devote attention to it voluntarily. Attention might not be sufficient for awareness (that is, you can attend to things without being aware of them), but it might well be necessary for awareness (you aren't aware of it without attention). The argument is about the latter point. The final sentence of your comment, though, is inaccurate. The phenomenon of inattentional blindness shows that unexpected objects are NOT apt to draw attention, and the fact that they are unexpected makes them LESS likely to be noticed.
Dr. Simons, the final sentence of my comment was prompted by reading this, from the Scholarpedia article on attention:
"The most effective orienting stimuli are loud sounds, suddenly-appearing bright lights, changes in contours, or movements in the peripheral visual field that are not regular, predictable occurrences. It is as though we had an internal 'model' of the immediate world of stimuli around us. When we notice a departure of stimulus input from that model, we reflexively orient to that stimulus in order to update that model as quickly as possible (Sokolov, 1975)."
That being noted, I don't want to take up any more of your time. Thank you for your time; your responses were helpful to me.
"Inattentional blindness or inattentional amnesia":
"For the amnesia account to hold, observers would have to consciously perceive the unexpected object and then forget that they saw it, something that might be less plausible when the unexpected object is particularly distinctive or unusual (e.g., a person in a gorilla suit)." Yes, but it is also implausible that the subject would fail to see a particularly distinctive object, such as a gorilla. As such, this does not seem to be a point against the inattentional amnesia interpretation.
DS- Not really. Yes, it's intuitively implausible that you could miss something like a gorilla. That's what makes the finding counter-intuitive and interesting. It's a different sort of implausibility for memory. It's not just counter-intuitive that they could forget it, but it runs against the extensive memory literature showing that distinctive things that you've consciously experienced are better remembered. In one case, in the perception case, it's counter-intuitive but consistent with the data. In the memory case, it's counter-intuitive but inconsistent with the data (the intuition is right that you would remember it better).
"Inattentional blindness or inattentional agnosia":
"However, evidence that the critical object can prime a subsequent response suggests that it is processed to some extent, even when it is not reported."
My response: The subsequent response is primed by perceptual classification that is not consciously accessible to the subject. This is consistent with an inattentional agnosia account according to which the subject is unable to consciously access semantic information for a visual stimulus although the subject's visual experience represents the color properties, shape properties, etc., of that stimulus.
DS - Was there a comment here? It might not have made it into the file.