[[Here are some selections from the paper - it is worth reading the whole.]]

In our ASSC20 symposium, “Does unconscious perception really exist?”, the four of us asked some difficult questions about the purported phenomenon of unconscious perception, disagreeing on a number of points. This disagreement reflected the objective of the symposium: not only to come together to discuss a single topic of keen interest to the ASSC community, but to do so in a way that would fairly and comprehensively represent the heterogeneity of ideas, opinions, and evidence that exists concerning this contentious topic. The crux of this controversy rests in no small part on disagreement about what is meant by the terms of the debate and how to determine empirically whether a state is unconscious or not.

These are issues that directly concern all of us who study consciousness, so it seems it would be in our best interest to strive for consensus. Given the conversation at ASSC20, we are pleased to have the opportunity to address some of the nuanced topics that arose more formally, and share some of the thinking we have done since the meeting. To reflect the heterogeneity of ideas and opinions surrounding this topic, we have organized this discussion into four distinct contributions.

—M.A.K.P. and I.P.

Practical and theoretical considerations in seeking the neural correlates of consciousness

Megan A. K. Peters

Psychology Department, University of California, Los Angeles, Los Angeles, CA90095,

As empirical scientists studying consciousness, we should be concerned with one question above all others: How can we design an experiment that will isolate the “conscious” processing of something from the “unconscious” processing of it, so that we can study the neural processing that underlies awareness – the neural correlates of consciousness (NCCs) – without inadvertently including a number of other confounds? This is the foundation of the scientific method.

Of course, this has always been the goal of studies seeking the NCCs, for example via comparing brain activity in “conscious” and “unconscious” conditions (Baars 1993). But a number of confounds continue to plague our experiments. My goal here, therefore, is to briefly enumerate the current practical concerns in experiments seeking to identify the NCCs, and to discuss how a newly developed paradigm can directly address these practical issues (Peters and Lau 2015).


Do these results mean that we can never achieve matched performance in “conscious” versus “unconscious” conditions, rendering the requirements for experiments seeking NCCs impossible to meet? Not necessarily. [[But maybe yes!!! Think about that.]] All we can infer from these results, for now, is that unconscious perception of the type we require seems to be harder to induce than the field may have realized. (We haven’t yet tried all the possible masking or neuromodulation techniques in existence.) Nevertheless, these experimental findings should make us think critically about what has actually been found in studies that do not control for task performance, may be susceptible to the criterion problem, or use masking or other manipulations to render a stimulus “unconscious”.

What we need to think about when we think about unconscious perception

Ian Phillips

St. Anne’s College, University of Oxford, OxfordOX2 6HS,

Theoretical discussions of unconscious perception typically focus on how consciousness should be operationally defined (Lau 2008Seth et al. 2008Irvine 2013). However, a compelling case of unconscious perception requires both evidence that consciousness is absent and that perception is present. Consequently, theorists must also consider how perception should be operationally defined, and assess alleged cases of unconscious perception accordingly.

Traditionally, it was assumed that to be perceived a stimulus must contribute to a subject’s conscious perspective (Moore 1925). To allow for the possibility of unconscious perception, Kanwisher suggests instead using “perception” to refer to “the extraction and/or representation of perceptual information from a stimulus, without any assumption that such information is necessarily experienced consciously” (2001, 90). Kanwisher’s proposal needs refinement. It risks counting distinctive allergic reactions as instances of perception (Dretske 2006). It also fails to secure the idea that perception is an individual-level phenomenon, not merely an occurrence in an individual’s visual system or brain (Burge 2010, 368 ff.).

By way of refinement, Burge proposes that perception is constitutively a matter of objective sensory representation by the individual. This means that perceptual states do not merely carry information but represent features of the physical environment as opposed to “idiosyncratic, proximal or subjective features of the individual” (2010, 397). According to Burge, such contents are attributable just when perceptual constancies are exercised. “Perception requires perceptual constancies.” (399).

An alternative approach focuses on the “role”, as opposed to “content”, of perceptual states. Thus, Dretske (2006) proposes that the information which perceptual states carry must be directly available for the control and guidance of action. Similarly, Prinz (2015) stipulates that perception involves the transduction of “useable” sensory information. Content and role approaches are not exclusive. Milner and Goodale understand perception to “refer to a process which [subserves] … the recognition and identification of [external] objects and events and their spatial and temporal relations” (1995/2006, 2). Here both content and role requirements are in play.

In line with contemporary orthodoxy, all the authors just mentioned claim that perception howsoever defined occurs unconsciously. [See also Block (2016) and Block in Block and Phillips (2016).] Here, I discuss four cases commonly invoked in support of this contention. Thinking about whether perception is genuinely present in these cases demonstrates that matters are much less clear cut than standardly supposed.


Proponents of unconscious perception face the challenge of providing an adequately justified operational definition of individual-level perception. Assessed in the light of extant proposals, many apparently clear cases of unconscious perception no longer appear so clear cut. Moreover, an obvious concern lurks in wait. One possible operational test for perception (closely associated with Dretske’s role-based proposal above) requires that the information carried by a perceptual state must be exploitable by a subject to make a discriminatory response. Yet this test for perception is equivalent to so-called “objective” measures of consciousness (i.e., above chance discriminative sensitivity) (Green and Swets 1966). As a result, no putative cases of unconscious perception can hope to avoid the familiar concern that they simply involve weak conscious awareness unreported due to a conservative response criterion (Eriksen 1960Holender 1986Phillips 2016; Peters, this symposium).