Visual Cortex

The visual cortex comprises interconnected cortical regions involved in vision. Primary visual cortex (V1) lies mainly in the occipital lobe. In the principal pathway supporting conscious vision, signals travel from the retina through the optic pathways and the lateral geniculate nucleus of the thalamus before reaching V1. V1 is therefore not the first part of the brain to receive retinal information.

Visual processing is distributed and recurrent. Areas commonly labelled V2, V3, V4 and MT/V5 have different response properties and connections; their numbers do not describe a simple series of seven increasingly complex processing stages. Processing continues through networks involved in recognising objects and guiding actions. The National Eye Institute's Thalamocortical Visual Processing Section describes its research into communication between visual thalamus and cortex.

2-Minute Neuroscience: Primary Visual Cortex — Neuroscientifically Challenged, by neuroscientist Marc Dingman. The animation shows where V1 is located, how information reaches it through the thalamus, and how its neurons contribute to analysing the visual scene. It explains visual processing rather than a mechanism of action for IEMT.

The visual field is the region of space visible while looking in a particular direction. Each cerebral hemisphere receives information about the opposite half of visual space from both eyes. This differs from saying that one hemisphere processes only one eye.

Visual-field loss, difficulty recognising an object and neglect of one side of space are different problems, although they may coexist. The site and nature of an impairment require assessment; they cannot be inferred simply from how someone describes an image in a therapy session.

Blindsight refers to residual responses to visual stimuli in a field where a person reports no normal conscious vision, typically after damage involving V1. Performance depends on the person, task and remaining pathways. It does not mean that a person has ordinary, unrestricted sight without knowing it.

For D.F., see the primary studies Structural and Functional Changes across the Visual Cortex of a Patient with Visual Form Agnosia and Pointing in the Visual Periphery: Is D.F.'s Dorsal Stream Intact? For T.N., see Neural correlates of body and face perception following bilateral destruction of the primary visual cortices.

These are informative individual cases with particular injuries and testing conditions. They help distinguish aspects of visual processing; they do not establish a treatment mechanism for IEMT.

Visual agnosia concerns recognition despite sufficient basic visual function for the task. Visual-field loss concerns the region of space in which vision is impaired. Hemispatial neglect concerns attention or awareness of one side of space. A description such as “cannot see it” may therefore require clarification rather than an immediate anatomical conclusion. See also Cerebral Hemispheres.

Prosopagnosia is difficulty recognising faces. A person may see facial features yet struggle to identify whose face they are seeing. It can occur as a developmental difficulty or after brain injury; it should not be assumed that every affected person has an acquired lesion in one specific structure. The NHS information on prosopagnosia describes its presentation and routes to assessment.

Regions of the fusiform gyrus contribute to face processing within a wider network. Naming a region involved in a task does not imply that it acts alone or that every recognition difficulty has the same cause.

Distinguish eyesight, visual recognition and a person's experience of mental imagery. The neuroscience of vision provides background to these distinctions, but does not show that changing gaze direction retrieves a particular kind of memory or identifies its truth. Record reported changes in imagery as reported changes, and seek appropriate assessment for visual or neurological difficulties.