Infants and young children cannot report their phenomenology. This has led some philosophers to argue that babies' consciousness must be limited. Even if we think that babies are conscious it might seem impossible to recover the particular character of their experience. A version of Block's abductive method can at least partially solve this problem. We can consider a wide range of functional and neural correlates of conscious experience in adults and then look to see similarities and differences in babies.

In adults attention is highly correlated with vivid consciousness. This consciousness has a particular subjective quality – “the spotlight” – with a defined – “brightly lit” – focus and surrounding darkness. Both phenomenologically and functionally, attention to one event seems to inhibit consciousness of other events – as in inattentional blindness.

There is a distinction between exogenous and endogenous attention. Exogenous attention is driven by information-rich external events. These events may be intrinsically salient. But exogenous attention may also be driven by subtle unexpectedness. Exogenous attention is marked by characteristic event-related potential (ERP) signatures, eye movements, decelerating heart rate, and parietal activation. Exogenous attention and vivid consciousness characteristically fade as information is obtained, a process of habituation.

Endogenous attention is the sort of top-down “paying attention” that is motivated by specific goals rather than by intrinsic interest. It has been the focus of the adult literature for methodological reasons, and endogenous and exogenous attention are often not distinguished in discussions of consciousness. Frontal activation seems to be particularly important for endogenous attention.

These functional features of attention correlate well with neurological patterns. In adult animals, endogenous attention leads to the release of cholinergic transmitters to some parts of the brain and inhibitory transmitters to other parts. Attention increases both the efficiency of a particular part of the brain and its plasticity; and it inhibits activation and plasticity in other brain areas.

So for adults there is an elegant if undoubtedly oversimplified story about how consciousness works. In the canonical case, the goal-directed control systems in frontal cortex indicate that a particular kind of event is important. The perceptual system, guided by attention, zooms in on just that event and the brain extracts information about the event and modifies itself, that is, learns accordingly. Significantly, though, this whole process is highly focused; other parts of the brain may actually be shut down in the process. Vivid spotlight consciousness is the phenomenological result.

Even very young infants have extensive exogenous attention capacities. When they are presented with even highly subtle and conceptually unexpected novel events, they immediately focus their gaze on these events, and show similar heart rate deceleration and ERP signatures to those of adults. Indeed, this is the basis for the habituation technique that is our principal source of information about infant's minds. However, infants develop endogenous attention much later, and it is still developing during the preschool years. Moreover, and probably correlated with this fact, infants and young children appear to have less focused attention than older children – for example, they show better incidental memory.

The neurology suggests a similar picture. The parietal and sensory systems involved in exogenous attention are on line at an early age. The top-down frontal regions and connections that control endogenous attention only mature later. Young animals' brains are far more plastic than adult brains and this plasticity is much less focused and attention-dependent. Cholinergic transmitters are in place early, while inhibitory transmitters emerge only later.

So again, an undoubtedly oversimplified but suggestive picture emerges. When infants and young children process information there is much less top-down control and inhibition. Infants are sensitive to any information-rich stimuli, not just those stimuli that are relevant to their goals and plans. And because they have much less experience, more stimuli will be information-rich for them than for us. With less top-down inhibition their processing and plasticity will be more distributed and less focused than those of adults.

These pictures also make sense from an evolutionary point of view. Childhood itself, that paradoxical period of helpless immaturity, is more protracted in species that rely heavily on learning – and most protracted in humans. Childhood reflects an evolutionary division of labor. Children are very good at learning about everything and are not very good at doing anything – adults use what they have learned in childhood to design effective actions.

As Block suggests, we can use this mesh of functional, neurological, and evolutionary facts to make a hypothesis about phenomenology. Babies are more conscious than we are. They are ceaselessly and broadly engaged in the kind of information-processing and learning that adults direct only at limited, relevant events. And babies are less subject to the processes that actively cause unconsciousness in adults – inhibition and habituation. When adults are placed in a situation that is functionally similar to babies, such as traveling in a strange country or meditating in certain ways, we experience a similarly vivid but distributed phenomenology – consciousness becomes a lantern instead of a spotlight.

For babies, consciousness may also overflow accessibility. But babies make the ambiguity of “accessibility” vivid. Obviously, information in infant consciousness is not accessible for reporting – it may also not be accessible for goal-directed planning nor be the subject of the endogenous attention that accompanies such planning. But it may indeed be accessible for purposes of induction, prediction, generalization, and intuitive theory-formation – the principal psychological activities of babies. Does that constitute overflow or not?

This leads to a broader methodological point, and to the greatest advantage of developmental data. Human adults are our chief source of information about consciousness. But in adults, many very different functional and neurological processes are highly correlated. Attention is focused, inhibitory, and top-down, and it leads to plasticity and learning, and it is reportable, and it is in the service of goals, and it is connected to a sense of self, and so on, and so forth. In development, this apparently unified picture breaks apart in unexpected and informative ways: Babies may have access for induction but not planning, have exogenous but not endogenous attention, and have plasticity and facilitation without inhibition. Rather than a single story of capital-c Consciousness, there may be many very varied relations between phenomenology and function.