To find the cognitive functions and neural processes that take us towards understanding the phenomenality of consciousness it is important to establish a boundary—a boundary with what we should call unconscious processing. This will by no means be an easy job (Lamme 2006). In fact, the whole issue of understanding consciousness and solving the explanatory gap is about positioning that boundary. There are situations where it is in fact unclear whether we should talk about a conscious sensation or not. Take the situation of a split-brain patient: here, a stimulus presented to the left visual field will be processed by the right half brain, typically devoid of communication via language. Hence, the subject will tell you that she did not see that stimulus. He may draw the stimulus, however, using his left hand. Or the left hand may point at the stimulus, or match it to a related subject (Gazzaniga 2005). Who are we to believe, then? The hand or the mouth? What types of behaviour may count as evidence for conscious sensations? Just speech? What about aphasic subjects, then? Similarly, there are conditions like neglect, or manipulations of attention (change blindness, inattentional blindness), where it is difficult to be entirely sure that what appears to be not seen is in fact maybe just not attended to, and hence forgotten or not cognitively accessible and hence not reportable (Lamme 2003, 2006, 2010). This uncertainty has sparked a lively debate on the nature of consciousness, its potential independence of cognitive functions like attention, working memory, or access (Lamme 2004, 2010a, 2010b), and whether consciousness can ever be separated from a report about consciousness (Block 2005, 2007; Dehaene et al. 2006; Cohen & Dennett 2011; Fahrenfort & Lamme 2012). This debate is all about the difference between seeing and knowing, between phenomenality and access (P-consciousness and A-consciousness), between qualia and higher-order thoughts. In this debate, the issue that seems unsolvable is where exactly the boundary between conscious and unconscious processing should be laid.
In such attempts to establish boundaries, it is perhaps good to start from the extremes, as an example from zoology will illustrate. Superficially, one could argue about whether a dolphin is a fish or a mammal. Science has resolved that argument by looking at animals that we all agree are either mammals (such as dogs, cows, or monkeys) or fish (such as sole, tuna, or piranha). From that perspective, the key differences between these species lies in the way they breathe and reproduce.[2] Why are these the key differences? Well, differences in breathing do all the explaining for why fish are generally more adept at living in water instead of on land. Similarly, evolution towards the land has called for eggs with protective layers (amnios), as anamniotic eggs (that fish lay) cannot survive on land. The most extreme version of that is the intrauterine development of the egg. Mammals and fish are thus at the two extreme ends of evolutionary adaptation towards breathing and reproducing on land.[3] We understand why a mammal behaves differently to a fish from these key properties. From these key properties we understand why mammals roam the surface of the earth, why they look the way they look, and why they behave the way they do.[4] In classifying animals, we use these features for a discrete taxonomy. This means that there are other features that do not qualify as defining characteristics, which are disregarded in animal taxonomy. Among these are behaviours like swimming in water, or living in groups. The key differences, obtained from looking at the extreme ends of the spectra, lead us to conclude that dolphins are mammals and not fish, even though appearances may suggest otherwise. We can draw a sharp boundary, and do not have to resort to saying that dolphins are “fishy mammals”, because we recognize that the swimming behaviour of dolphins is irrelevant to their taxonomy.[5] Defining features and irrelevant features enables a proper and discrete taxonomy, making most sense of all the available data. Moreover, a taxonomy based on such features allows for an understanding that goes towards a deeper level, in this case the evolutionary pressure that came from the transition from sea to land dwelling.
I propose to undertake something similar with consciousness. What is the proper taxonomy of conscious versus unconscious vision? What are the defining features of this difference, and what features are irrelevant? And do the defining features take us towards a somewhat more fundamental level of understanding consciousness (Lamme 2010a, 2010b)? To find those features, we start from the extreme ends: the mammals and fish of consciousness research, the things most people will agree on as representing either conscious or unconscious processing.