As mentioned previously, the very basic form of the motor theory has the problem of being incapable of distinguishing conscious and unconscious action. Here a solution may be adapted from a similar problem that arises in distinguishing conscious from unconscious perception. Not just any input to sensory systems gives rise to a conscious percept. Instances of subliminal perception and blindsight are two kinds of example. The solution I advocate for distinguishing conscious from unconscious perception is twofold. I shall label the two parts of the solution “intermediacy” and “recurrence.” The first part, intermediacy, involves identifying conscious perceptual states with states at relatively intermediate levels of sensory processing hierarchies. The second part, recurrence, restricts consciousness to intermediate-level states involved in recurrent interaction between representations at relatively high and at relatively low levels of sensory processing hierarchies.
The “what” and “why” of intermediacy. Sensory processing, as in for example, vision, is hierarchical, with the lowest levels constituted by neural activations close to the sensory periphery which represent local and egocentric visible features and the highest levels constituted by abstract and allocentric representations employed in categorization and recognition.
It is natural to ask where in a sensory processing hierarchy conscious states reside. It is crucial to any account of consciousness that it connect the reality accessible from the third-person point of view (e.g. states of activation in neural circuits) with the appearance of what it’s like from the first-person point of view. Further, both introspective and observational methods converge to indicate that conscious states are relatively intermediate between the highest and lowest levels of the hierarchy. My visual perception of a coffee cup represents the cup as having a specific orientation relative to my point of view and relatively specific location in my visual field. However, the percept is not so high-level as to merely indicate the presence of a cup in a way abstracting from all observer-relative information. Nor is it so low-level as to register every change in irradiation of various regions of my two retina (the lowest levels are prior to even the integration of information from the disparate retinas). The intermediacy criterion on sensory consciousness means that not just any neural response to a sensory input will count as a conscious percept. This goldilocks criterion will exclude from consciousness those neural activations that are too high or too low.
The “what” and “why” of recurrence. While intermediacy is necessary, it seems not to alone suffice for consciousness. Strictly feed-forward activation of representations in sensory processing hierarchies can occur without consciousness. Pascual-Leone and Walsh (Pascual-Leone & Walsh, 2001) showed, with precisely timed pulses of transcranial magnetic stimulation, that visual consciousness was suppressed if recurrent activation was suppressed and only feed forward was allowed. Additionally, Lamme et al. (Lamme, Supèr, & Spekreijse, 1998) suggest that responses to stimuli in animals under general anesthetic are feed-forward activations without accompanying recurrence.
Elsewhere I defend what I call the Allocentric Egocentric Interface theory of consciousness (AEI) (P. Mandik, 2005, 2009). AEI incorporates both intermediacy and recurrence in the following manner: conscious states are intermediate-level states in processing hierarchies which, the intermediate states, are constituted by pairs of recurrently interacting allocentric and egocentric representations. Previous discussion of AEI has focused on sensory processing hierarchies. I turn, in the next post, to consider a natural extension of AEI to motor processing hierarchies.