Apparent Motion: fMRI and EEG Evidence for the Where and When of Visual Consciousness Does not Support the Multiple Drafts Model

Abstract

Descartes posited a soul, a homunculus residing inside the Cartesian Theatre of the pineal gland experiencing phenomenal visual consciousness. This explanation for visual consciousness requires an explanation for how the homunculus comes to see and leads to an infinite regress of eyes and images. This fallacy is a red flag alerting us to a question in the science of consciousness; how do our explanations of visual consciousness overcome the infinite regress? Dennett & Kinsbourne (1992) attempt to redress the homunculus fallacy by annihilating the omnipotent Cartesian homunculus within their Multiple Drafts model. They propose that: it is not possible to scientifically untangle early neural processing in sensory occipital cortex from later processing in a brain wide global neuronal network; that processing in occipital cortex is unconscious, asynchronous, and does not involve filling-in; that there is a temporal disjunction between the neural processors which are doing the representing and the conscious content which is being represented; and that the onset of processing in occipital cortex does not align with the onset of the content of consciousness. The contention that there is a temporal disjunction between neural processing and the content of phenomenal consciousness is not supported conceptually nor empirically. The temporal frame of the represented (phenomenal experience) aligns with the temporal frame of the neural processing that is doing the representing, and these correlations are accessible to scientific investigation. In addition, scientific evidence does not support the other principles of the Multiple Drafts model. fMRI activity within the V1/V2 retinotopic maps correlates with the experience of colour and motion filling-in, in a phenomenally and spatially specific way. Moreover, EEG activity correlates with the onset and duration of neural processing in V1/V2 that gives rise to the illusory motion experience. Phenomenal evidence suggests that shape and motion, and shape and colour processing in occipital cortex are interdependent and thus synchronous. This interdependence is supported by an emerging laminar layer, single neuron level explanation, where feedback from occipital cortex V4 and V5 supports colour and motion filling-in, in V1/V2. In conclusion fMRI and EEG activity in occipital cortex correlates phenomenally, spatially and temporally with visual illusions of colour and motion filling-in. This activity is interdependent, synchronous, and constructs the filling-in of motion and colour representations in occipital cortex. The neural processors underpinning visual representations are locatable in space and time in occipital cortex, with the onset of a neural activity marking the onset of phenomenal consciousness. An emerging reductive explanation for these illusory experience suggests the solution to the infinite regress of the homunculus is to be found in patterns of occipital cortex processing. This evidence undermines the Global Neuronal Workspace as a viable model for explaining visual consciousness.