In a recent paper by Bert Timmermans they compared: i) the Perceptual Awareness Scale (PAS) ii) confidence ratings (CR) and iii) post-decision wagering (PDW) which are all scales of measuring consciousness. Although other measures do exist these are more commonly used to measure subjective awareness, and a systematic overview of them was long overdue.
What is the Perceptual Awareness Scale?
The PAS was originally developed by Ramsoy and Overgaard (2004) in an experiment during which participants were asked to describe the quality of their visual experience when presented with briefly displayed visual stimuli. It is a 4 point scale where:
1 = no experience
2 = brief glimpse
3 = almost clear image
4 = absolutely clear image
Because of the way it was developed (letting the original pilot participants choose the categories) the creators claim that the scale is intuitive. Additionally there is no suggestion of a correct answer, something important in subjective scales. The fact that participants are directly asked to rate their own experience is also claimed, rather paradoxically, to be both an advantage and a disadvantage. If the participants are good at introspection, asking them directly minimizes errors and confusion. If they’re not, however, asking them to report on their own experience is seen as a great risk. This could be true of any subjective rating scale in which introspection is required, however.
What are Confidence Ratings?
Confidence Ratings have been used in both perception and to allow participants to rate their own performance. When used to rate how confident a participant is of seeing or perceiving a stimulus, it is considered to resemble the PAS. When used as the latter, it is more of a meta-cognition task; that is, it involves thinking about thinking. There are different scales of CR, but all will include a no confidence or guessing category. Because of its similarity with the PAS, in many ways it has the same advantages and disadvantages. However, on one point it does pull ahead — participants are not directly asked to introspect, and so even bad introspections may not skew the results.
What is Post-Decision Wagering?
Having performed a task, post-decision wagering involves placing a wager on your own performance with either real or imagined money. In this task you use your own awareness of performance to judge experience. No introspection is required during this task perhaps making it easier for poor introspectors. PDW is a recently suggested measure (2008), put forward as an objective or direct measure. It’s direct, because the degree to which a participant wagers indicates consciousness experience. The possibility to gain real (or imaginary) money provides the participants with a strong incentive to reveal what they think they have experienced. However, PDW has been questioned from a theoretical point of view. Is it a direct measure of awareness? Seth and colleagues(2008) think it is not direct, but rather a way around asking participants to introspect.
In Timmerman’s paper, the results indicated that the PAS performed strongly for performance-awareness, significantly more so than CR or PDW, particularly for low stimulus intensities. This implies that the PAS is the most sensitive measure between the three.
Although Deines and Seth (2008) went on to dispute this claim, saying that the fact that visual content is consciously seen does not mean that the content is relevant to a decision, Timmermans replied that there is a difference between conscious visual experience (which can be partial) and the resulting experience (which is conceptual, and often stitched together from partial information). Whether or not visual and conceptual consciousness can be separated it is clear we still have some way to go in understanding subjective consciousness and how to measure it.
“For example if one saw a square but was only aware of seeing a flash of something, then one has not consciously seen a square,” Deines and Seth (2008)