Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Vision

Vision can contribute to consciousness, but it is not necessary for consciousness. The biological mechanism of consciousness does not require sensory input, although some minimal level of activity is required for the autonomic nervous system to provide for the sense of self. The minimal level of neural activity or threshold for the sense of self is unknown.

Successive Plate-Like Stages

The initial stages of the mammalian visual system have the plate-like organization often found in the Central Nervous System. The first three stages are housed in the retina; the remainder are in the brain: in the lateral genetic geniculate bodies and the stages beyond in the cortex.(diagram) (Hubel: Eye, Brain, and Vision, 27)

Three retinal layers: Light has to pass through the ganglion cells and bipolar cell layers before it gets to the rods and cones.(diagram) (Hubel: Eye, Brain, and Vision, 37)

Research Study — Synaptic Organization of Visual Space in Primary Visual Cortex

Research Study — Thalamocortical Signals Selectively Amplified via Recurrent Inputs

Research Study — Attention Modulated Top-Down, Selectively Processes Information

Research Study — Visual Space Compressed in Prefrontal Cortex

Research Study — Visual Circuitry Motion Detection

Research Study — Sensory Stimulation Shifts Visual Cortex from Synchronous to Asynchronous

Convolution of Vision and the Sense of Self

LGN receives fibers from the optic tract conveying impulses from both retinae. LGN is laminated, and the inflow from each retina projects on different laminae (ipsilateral retina to laminae II, III, and V, contralateral retina to laminae I, IV, and VI).( Afifi; Functional Neuroanatomy, 250)

Eyes do not hold perfectly still but make constant tiny movements called microsaccades, which occur several times per second and are more or less random in direction and about one to two minutes of arc and amplitude. (Hubel: Eye, Brain, and Vision, 81)

Visual Perception and Memory in Higher Neuronal Assemblies of Visual Hierarchy

Visual perception is formed in a hierarchy of neuronal assemblies extending from the primary visual areas of posterior cortex, through the association areas of parietal cortex, the interpretive areas of temporal cortex, and into the frontal cortex. Perception is associated with sparse but widespread neural activity in the higher levels of the ever widening receptive fields this visual hierarchy. Visual memory is mediated by synaptic plasticity in the sparse but widespread neural activity patterns in the higher association cortex.

Evolution has provided primates with a complex patchwork of visual areas occupying the posterior 50% or so of the cerebral cortex. (Milner; Visual Brain, 128)

Dynamic Core Implies Sparse but Widespread Activity Patterns

Areas of the higher visual cortex and other areas of the association cortex may often form a part of the dynamic core, but no particular areas or specific neuronal assemblies form an essential part. These visual cortex areas can be inactive, and the person will remain conscious. My current hypothesis is that a minimal dynamic core requires sparse but widespread activity patterns in portions of working memory, thalamocortical loops, and the limbic system for ongoing successive intervals of a few hundred milliseconds.

Activity in V1 may be necessary for vivid and veridical visual consciousness (as it is activity in the retinae), but the firing of none of the neurons in V1 directly correlates with what we consciously see. (Crick & Koch; Consciousness and Neuroscience, 43)

Neural Correlates of Visual Consciousness

Although there are many different visual regions, each of which analyzes visual input in different and complex ways, we can locate no single region in which the neural activity corresponds exactly to the visual picture of the world we see in front of our eyes. (Crick; Astonishing Hypothesis, 159)

Consciousness research work or monkeys and other mammals has focused on the question of whether the correlates of visual consciousness is located in primary visual cortex (V1) or later visual stages. (Chalmers; Vision and Consciousness, 123)

When you’re looking at the “fine print” of a legal statement, or using a 10x lens to examine the intricate structure of an insect, I suspect the NCC of the mental image would be formed by the neural hierarchy of the visual system, including area V1.

Patients with extensive damage to the early visual cortices lose their ability to generate visual images. (Damasio; Descartes' Error, 101)

It is unlikely that information sent along the pathway from V1 to the superior colliculus, responsible for controlling and initiating eye movements, can produce visual awareness. (Koch; Neuronal Substrate of Visual Consciousness, 252)

Hypothesizing that the activity in V1 does not directly enter awareness. (Koch; Neuronal Substrate of Visual Consciousness, 253)

What does enter awareness is some form of neural activity in certain higher visual areas, since they do project directly to frontal areas. (Koch; Neuronal Substrate of Visual Consciousness, 253)

Research Study — Visual Cortex and Consciousness

Cortical visual organization

First principle of cortical visual organization: Two major corticocortical pathways, each beginning with primary visual cortex. (1) Ventral pathway is directed into the inferior temporal cortex and is important for visual object recognition, (what) an object is. (2) Dorsal pathway is directed into the posterior parietal cortex and is important for spatial perception, (where) an object is. (Webster; Neuroanatomy of Visual Attention, 22)

Cortical visual areas — Dorsal route, Ventral route. (Pinel; Anatomy of Human Brain, 136)

Second principle of cortical organization: Cortical areas within a pathway are organized hierarchically. Projections from lower-order areas to higher-order areas originate mainly in layer III of cortex and terminate predominantly in layer IV. 'Feedforward' projections. (Webster; Neuroanatomy of Visual Attention, 23)

Projections from higher-order areas to lower-order areas originate mainly in layers V and VI of cortex and terminate both above and below layer IV, but not in layer IV. 'Feedback' projections. (Webster; Neuroanatomy of Visual Attention, 23)

Connections between areas at the same hierarchical level. Terminals vary their laminar pattern from one patch to another; terminals homogeneously distributed across all layers. 'Intermediate' projections. (Webster; Neuroanatomy of Visual Attention, 23)

Average receptive field size increases as one progresses along visual pathways, consistent with the notion that receptive fields of cells in later areas are built up from receptive fields of earlier areas. (Webster; Neuroanatomy of Visual Attention, 24)

Research study — Visual Cortex Functional Microcircuits

Visual Processing through Modular Stages

Visual input is processed through a sequence of stages that includes edge detection, feature extraction of varying complexity, and normalization for size, position, and orientation. The resulting neural representation is then compared with memory objects. (Ullman; Sequence Seeking Counterstreams, 257)

Link to — Convergence Zones for Language

Both physiological and psychophysical studies have shown that movement is extracted early in the visual system as a primitive. (Koch; Neuronal Substrate of Visual Consciousness, 249)

Modular system for visual processing, with different areas within each pathway responding to different features. The number of these specialized areas has been estimated at about 30. (Robertson; Attention and Parietal Function, 257)

In sensory systems such as vision, multiple cortical regions that are functionally segregated (e.g., color, movement, orientation), can exceed thirty in number, distributed all over the brain. (Edelman; Wider than the Sky, 36)

Visual awareness cannot be thought of as the end product of a hierarchical series of processing stages. Instead, it involves the entire visual pathway as well as the frontal-parietal areas, which are involved in higher cognitive processing. (Logothetis; Window on Consciousness, 88)

"Form" Pathway and "Where" Pathway

Major visual processing pathways of the primate brain. Information from the retinogeniculostriate pathway enters the visual cortex through area V1 in the occipital lobe and proceeds through a hierarchy of visual areas that can be subdivided into two major functional streams. (Van Essen; Dynamic Routing Strategies, 284)

The "form" pathway leads ventrally through V4 and inferotemporal cortex (IT) and is mainly concerned with object identification, regardless of position or size. (Van Essen; Dynamic Routing Strategies, 284)

The "where" pathway leads dorsally into the posterior parietal complex, and is concerned with the locations and spatial relationships among objects, regardless of their identity. (Van Essen; Dynamic Routing Strategies, 285)

Cortical visual areas and some of their connections to major pathways from area V1. Processing stream for analyzing the visual form and quality of objects follows a ventral route into the temporal lobe. Processing stream for analyzing object location follows the dorsal root into the parietal lobe. (diagram) (Squire & Kandel; Memory, 87)

Two distinct processing streams arise from area V1. (LaBerge; Attentional Processing, 104)

The ventral stream (V1 to V2, V1 to V3, V1 to V4) flows ventrally toward the visual areas of the temporal lobe that are necessary for the discrimination, identification, and recognition of objects. (LaBerge; Attentional Processing, 104)

The dorsal stream (V1 to V5, V1 to V2) flows toward the visual area of the parietal lobe that are necessary for spatial perception and visually guided actions. (LaBerge; Attentional Processing, 104)

Neural Interaction between Areas

Neural response data suggests a high degree of neural interaction between areas of the cortex that are responsible for veridical spatial perception (dorsal pathways) and other areas that code features and objects and perhaps implicit spatial information (ventral pathways). (Robertson; Attention and Parietal Function, 274)

Binding or conjunctions of features that enter awareness require a high level of spatial representation. (Robertson; Attention and Parietal Function, 275)

Visual awareness of more than one object may require the accurate computation of space from a variety of spatial maps. (Robertson; Attention and Parietal Function, 275)

Modularity of Face Processing In Temporal Lobe Cortex

The face processing system in the temporal lobe is a network composed of multiple, functionally specialized nodes. The entire network of temporal lobe face patches constitutes a dedicated brain system for the processing of the high-level object category of faces. This system contains one region that provides for population coding of identity across view conditions using a hybrid representation of both course and sparse elements.

Research Study — Perception, Face Recognition

Cortical visual processing

Biological usefulness of visual consciousness in humans is to produce the best current interpretation of the visual scene in light of past experience (either our own, or that of our ancestors embodied in our genes), and to make this interpretation directly available for sufficient time to the parts of the brain that contemplate and plan voluntary motor output such as movements or speech. (Carter; Mapping the Mind, 204)

Visual system -- from eye to cortex. (Pinel; Anatomy of Human Brain, 134)

Research Study — Visual System Learning via Statistics of Natural Scenes

Television and Movie Flicker

Television and movie mechanisms are designed to produce successive images faster than human vision can respond. The resulting illusion is continuous motion. To avoid flicker, individual frames are renewed about 30 times per second. Because younger people’s nerves respond faster than those of older people, younger people may notice flicker in cases where older people do not.

Excerpts from science experts

V1, primary visual cortex, Brodman's area 17. (Damasio; Descartes' Error, 91)

Early visual cortices (V1, V2, V3, V4, V5) - (diagram) (Damasio; Descartes' Error, 91)

Brain maps V1

LGN

Six layers of LGN of a macaque monkey. - (diagram). Each layer gets input from only one eye. (Crick; Astonishing Hypothesis, 130)

Visual system, LGN, (Neuroanatomy, 328, 152, 154)

(Neuroscience 259)

(Crick; Astonishing Hypothesis, 135, 149)

Remembered Present (Gerald Edelman)

Visual Bistable Percepts

Knecker cube. (Koch; Quest for Consciousness, 269)

David H. Hubel, Eye, Brain, and Vision, Scientific American Library, 1988, ISBN 0-7167-5020-1

Read upside-down text.

A good reference for vision and the eye. (Purves, Neuroscience, 229, 259)

Link to — Consciousness Subject Outline