More goodies from Hakwan Lau’s lab — this article by Peters and Lau (2015) is of direct interest to Dr Bert Timmermans‘ lecture on measures of consciousness. It is highly probable that some processing of the outside world goes on outside of awareness, either by unconscious perception as shown by priming studies (but Sid Kouider would argue that we just perceive the stimulus at a different level, partially), or simply by us not always being able to identify what influences our behaviour (the highly controversial notion of unconscious behavioural priming). But what constitutes “unconscious perception”?
Researchers have been using both the objective and subjective threshold model. In the first, a stimulus is considered conscious as soon as a direct measure (decision task: did you see a word or not) shows above-zero sensitivity. Even if the person still claims they haven’t seen anything, subjectively. And unconscious influences can only be observed with indirect measures (such as the influence of an unseen primed word “table” on recognition of the subsequently presented word “chair”). Still, many researchers, especially in the field of implicit learning*, have been using a subjective threshold. A subjective threshold holds that as consciousness is inherently subjective, something is unconscious as soon as people can’t report it. So an above-zero sensitivity in a direct (decision) task in the absence of reported subjective awareness is proof of unconscious processing.
This paper by Peters & Lau suggest however that there may not be any unconscious perception as defined by the subjective threshold: when people report no subjective awareness (i.e. are at subjective threshold), they also show zero sensitivity in the decision task (i.e. are at objective threshold). So, objective and subjective thresholds coincide! In their words “This surprising finding suggests that the thresholds for subjective awareness and objective discrimination are effectively the same: if objective task performance is above chance, there is likely conscious experience.” Indeed, at least for briefly presented stimuli, this is also something we observed some while ago (Sandberg, Timmermans, Overgaard & Cleeremans, 2010), and which gives hope, in that it suggests that when done correctly, simply asking people what they saw is a sensitive enough measure. It also means that there may not be such a thing as unconscious perception at the subjective threshold (even if our 2010 results suggest that unconscious information may just start playing a role once conscious information seeps though). Whether the both objectively and subjectively “unseen” information would still leave enough of an activation trace to influence behaviour on a subsequent indirect task remains… to be seen!
Update: keep in mind that there is a caveat, in that it might just be that confidence ratings (which is the subjective measure they use) simply do not tap into subjective awareness, and that it is very much linked to the system’s metacognitive knowledge about how well it is doing, a function that can be executed both consciously and unconsciously. In other words, confidence ratings may not be exclusive, i.e. may be reflecting the also the presence or absence of Unconscious knowledge, like when you rate your confidence in a task based on a “hunch”. Also, it may be that over the course of the experiment, confidence ratings thus come to tap into the same unconscious knowledge as task performance, in that the system/person has learned the task, and also the distribution of their performance accuracy… unconsciously!
[* In IL, something is only conscious if a person reports on it. Now, for implicit learning this is understandable, because you’re trying to exclude knowledge of rules (of an artificial grammar for instance) while showing people’s above-zero sensitivity to rules they never knew were in the material, and an objective threshold would mean that you would have no proof of learning whatsoever and hence would assume all learning is conscious.]