We often measure unconsciousness from subjective and objective methods. What are the two methods based on? What's the difference? Better give some reference.
Objective measurement is based on how well people perform a task, irrespective of what they experience while performing the task. Subjective measurement on the other hand refers to measures that have to do with what people say they actually experience. In a disorder called "blindsight" for example, patients with a lesion in their primary visual cortex say they have no visual experience in a large part of their visual field (i.e. they are subjectively blind). When forcing these patients to guess about the location of an object in this part of their visual field, they show above chance performance (i.e. they are objectively able to point out the location of objects with above chance performance, even though they are subjectively blind). Other ways of investigating effects of "unconscious" information on objective performance has been by looking at subliminal priming, i.e. the effects that an unconscious stimulus can have on performance when detecting/categorizing a conscious target stimulus. See for example Dehaene, S., Naccache, L., Le Clec'H, G., Koechlin, E., Mueller, M., Dehaene Lambertz, G., et al. (1998). Imaging unconscious semantic priming. Nature, 395(6702), 597–600.
The difference between objective and subjective performance, as well as the question whether objective and/or subjective performance is enough to determine whether someone is conscious of a stimulus or not was a topic of debate about three decades ago (e.g. see Greenwald, A. G., Klinger, M. R., & Liu, T. J. (1989). Unconscious processing of dichoptically masked words. Memory & Cognition, 17(1), 35–47. VS Holender, D. (1986). Semantic activation without conscious identification in dichotic listening, parafoveal vision, and visual masking: A survey and appraisal. Behavioural Brain Sciences, 9, 1–23.).
There is still no consensus about whether to use objective or subjective performance to determine whether something is consciously perceived or not. The problem with subjective performance (just asking "did you see something, yes or no") has been that it it is prone to criterion changes. For example, someone might be much more prone to answer that they did not see anything when 90% of the trials are non-targets, than when only 10% of the trials are non-targets. This is something that can partially be solved using signal detection theory, by determining not only the number of hits, but also the number of false alarms. But much of it hinges also on the way the question is framed, and how they respondent is encouraged to answer ("yes/no" type question seem to naturally tap more into subjective experience, whereas two-alternative forced choice questions tap more into objective performance, although both types of questions can be framed in such a way that they tap into either, depending on what the instructions look like). In many papers people use some objective measure, sometimes in addition to a subjective measure.
Recently, people have extended the signal detection framework to be able determine "metacognition", which is the degree to which a subject "knows" about the correctness of their responses. In metacognition, subjects give a confidence rating that indicates how confident they are that their response is correct. The metacognition score can be seen as a "subjective measurement" about "objective performance" although the jury is still out as to whether metacognition really taps into experience itself (consciousness), or just into the degree to which a system can reflect on the accuracy of its decisions. The decision process necessarily conflates the metacognition measure. A recent paper from our group shows that metacognition for object detection is different from metacognition for object categorization (see here: Meuwese, J., van Loon, A. M., Lamme, V. A. F. & Fahrenfort, J. J. (2014). The subjective experience of object recognition: comparing metacognition for object detection and object categorization. Attention Perception & Psychophysics.).
There are many more things to say about this, but this post is getting too long already. Hope this helps.
This paper tackles directly your question: https://www.researchgate.net/profile/Arnaud_Destrebecqz/publication/259877740_Dissociating_Conscious_and_Unconscious_Learning_With_Objective_and_Subjective_Measures/links/0c96053a0487a09756000000.pdf
Article Dissociating Conscious and Unconscious Learning With Objecti...
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