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Letter
Can No-Report Paradigms Extract True Correlates of Consciousness? Morten Overgaard1,* and Peter Fazekas1,2,* In a recent Trends in Cognitive Sciences article, Tsuchiya et al. discuss how ‘noreport paradigms’ may be an important methodological remedy to isolate neural correlates of consciousness ([1_TD$IF]NCC) [1]. The article reflects the still ongoing attempt for consciousness research to answer its fundamental methodological question: how one can measure subjective experiences that are directly available only to the person having them. It was argued that experiments in which participants give a subjective report as a measure of consciousness are confounded by neural events relating to metacognitive/ introspective access to the conscious state and accordingly are more unreliable than experiments without reporting. It was, however, also briefly acknowledged that experimental paradigms without report risk other kinds of confounding, although these were never explored in the review article. In this letter, we wish to draw attention to two such problems, two fundamental weaknesses of noreport paradigms that might result in the possible overestimation or even the misidentification of NCCs (Box 1).
know that a particular no-report paradigm measures consciousness and not something else? One intuitive answer could be that if a particular type of behaviour or phenomenon has been found to be associated with subjective experience in previous experiments using subjective reports, this behaviour or phenomenon can be used as an ‘objective measure’ to replace the report. However, any such method can avoid confounding NCCs only to the degree that these objective measures do. If they happen to be associated not just with conscious experience but also with certain pre-conscious or post-conscious (i.e., cognitive) processes as well, their use in no-report paradigms will similarly result in the overestimation of NCCs by the corresponding pre- and post-NCC events.
Take, for example, binocular rivalry, which, as a prime example of a no-report method, is discussed in detail in the target article. No-report paradigms based on binocular rivalry utilise ‘perceptual readouts’ like eye movement (optokinetic nystagmus) or change in pupil size (pupil dilation) as objective measures of the presence of perceptual switches [2]. By measuring perceptual switches no-report paradigms aim to measure alternations in conscious percepts; however, switches are found at a whole range of levels of the perceptual hierarchy, including early (i.e., pre-conscious) stages of information processing [3]. Moreover, associated eye movement and change in pupil size are known to reflect pre-conscious events, If one is to avoid using subjective reports, like, for example, retinal image stabilisation one is forced to answer the obvious ques- [4] and norepinephrine release from the tion: without relying on reports, how do we locus coeruleus [5], respectively. The Box 1. The question of which activations in the brain may constitute NCCs has been discussed for decades in cognitive neuroscience. This research nevertheless faces the challenge of methodologically differentiating activations occurring before those directly related to subjective experience (pre-NCCs) from those that follow from or occur just after subjective experience (post-NCCs) [1,2]. Experiments using contrastive analysis (e.g., neuroimaging experiments) risk confusing NCCs with pre- or post-NCCs, as activations before and after the activations directly relating to subjective experience may differ between conditions.
target article carefully argues that noreport techniques have been proved to show that some neural activity that had previously been identified as NCCs were, in fact, post-NCCs. However, these noreport paradigms can still overestimate NCCs by including certain pre-NCC activity. Furthermore, no-report paradigms are also not immune to confounds related to post-NCC events. The physical act of reporting is rarely taken to be the greatest post-NCC confound. Rather, these are typically introspective acts, directing attention towards the contents of experience, metacognitive reflections over what has been experienced, associations, etc. [6,7]. Refraining from issuing a verbal (or other) report obviously does not rule out that participants in experiments are still introspecting, reflecting, associating, and so on. Nevertheless, Tsuchiya et al. consider binocular rivalry and ambiguous stimuli as candidates for ‘introspectionfree’ methods. But what reasons could one have to think of, say, a binocular rivalry experiment without report as a method to investigate conscious experience per se in the first place? Arguably, the only reason can be that one introspectively attends to what it feels like to experience binocular rivalry. In other words, the only way to invent a measure of consciousness without asking participants to report seems to depend on the scientist's own intuitions, which could hardly be said to be any less based on introspection [8]. Taken together, no-report paradigms seem just as confounded as report paradigms – in similar ways but for different reasons. One alternative to ‘choosing sides’ is to attempt an increased understanding of the interplay between mental and neural processes related to early, unconscious states, conscious states, and introspection. Although rarely explored, some experiments have investigated the manipulation of introspective
Trends in Cognitive Sciences, Month Year, Vol. xx, No. yy
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access to consciousness using different methods for report [9], using explicit instructions to increase introspective awareness [10], or using reports of graded first-order experiences [11]. Yet other experiments have combined report paradigms with no-report paradigms and specifically investigated the effect of reporting [12]. Such experiments suggest ways to acquire knowledge of how to understand and operationalise experience, introspection, and report and may result in future methodological tools to differentiate NCCs from pre- and post-NCCs. Acknowledgments The study was supported by the Danish Council for Independent Research and FP7 Marie Curie Actions –
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COFUND DFF-Mobilex Mobility Grant 1321-00165[2_TD$IF] and FWO Postdoctoral Fellowship 1.2.B39.14N (P.F.).
5. Einhäuser, W. et al. (2008) Pupil dilation reflects perceptual selection and predicts subsequent stability in perceptual rivalry. Proc. Natl. Acad. Sci. U.S.A. 105, 1704–1709
Cognitive Neuroscience Research Unit, CFIN, Aarhus
6. Aru, J. et al. (2012) Distilling the neural correlates of consciousness. Neurosci. Biobehav. Rev. 36, 737–746
University, Aarhus, Denmark Department of Philosophy, Aarhus University, Aarhus, Denmark
7. Overgaard, M. (2004) Confounding factors in contrastive analysis. Synthese 141, 217–231
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*Correspondence: morten.storm.overgaard@cfin.au.dk (M. Overgaard) and
[email protected] (P. Fazekas).
8. Overgaard, M. (2015) The challenge of measuring consciousness. In Behavioural Methods in Consciousness Research (Overgaard, M., ed.), pp. 7–19, Oxford University Press
http://dx.doi.org/10.1016/j.tics.2016.01.004
9. Marcel, A. (1993) Slippage in the unity of consciousness. CIBA Found Symp. 174, 168–180
References 1. Tsuchiya, N. et al. (2015) No-report paradigms: extracting the true neural correlates of consciousness. Trends Cogn. Sci. 19, 757–790
10. Overgaard, M. et al. (2006) The electrophysiology of introspection. Conscious. Cogn. 15, 662–672
2. Naber, M. et al. (2011) Perceptual rivalry: reflexes reveal the gradual nature of visual awareness. PLoS ONE 6, e20910 3. Sterzer, P. et al. (2009) The neural bases of multistable perception. Trends Cogn. Sci. 13, 310–318 4. Abadi, V.M. and Pascal, E. (1991) The effects of simultaneous central and peripheral field motion on the optokinetic response. Vision Res. 31, 2219–2225
11. Sandberg, K. and Overgaard, M. (2015) Using the perceptual awareness scale (PAS). In Behavioural Methods in Consciousness Research (Overgaard, M., ed.), pp. 181– 195, Oxford University Press 12. Frässle, S. et al. (2014) Binocular rivalry: frontal activity relates to introspection and action but not to perception. J. Neurosci. 29, 4403–4413
