Visual Cortex and Visual Processing

Medial Side of the Brain

• Drawings depict the medial view of the brain, emphasizing structures like the corpus callosum, central sulcus, and calcarine sulcus.

• The corpus callosum allows communication between the two hemispheres and appears slightly tilted in the medial view.

Key Sulci and Cortices

• Central Sulcus: Separates the frontal and parietal lobes.

• Calcarine Sulcus: Located on the medial surface of the occipital lobe, it separates primary visual areas and is crucial for visual processing.

• Areas:

• V1 (Primary Visual Cortex): Situated at the back of the occipital lobe, shaped somewhat like a triangular slice.

• V2 & V3: Secondary areas that wrap around V1, participating in visual processing.

• V4: Processes color; damage may result in achromatopsia, a form of color blindness caused by issues in visual processing, rather than retinal defects.

• V5: Notably processes motion, localized more laterally.

Information Organization in Visual Processing

• Visual processing involves multiple areas with varying functions: primary (V1), secondary (V2, V3), and tertiary areas (V4, V5). Each area specializes in specific visual attributes:

• V1: Striate cortex for basic visual input.

• V2: Thin and thick stripes; receives from V1.

• Blobs: Regions in V1 sensitive to color, receiving from parvocellular layers.

• Interblobs: Process form and motion, receiving from magnocellular layers.

• Thick and Thin Stripes:

• Thick Stripes: Motion processing (receive from interblobs).

• Thin Stripes: Color (receive from blobs).

• Pale Zones: Information about form.

Ventral and Dorsal Streams

• The ventral stream (temporal lobe) is the "what" stream, processed for object recognition (e.g., faces).

• The dorsal stream (parietal lobe) is the "where" stream, crucial for spatial awareness and visual guidance of actions.

Face Processing Areas

• Fusiform Face Area: Located in the ventral stream, specialized for facial identification and recognition.

• Superior Temporal Sulcus: Processes dynamic features of faces, important for recognizing emotions through facial expressions.

Object Recognition and Place Recognition

• Parahippocampal Place Area: Activates during processing of environments, landscapes, and spatial contexts, crucial for navigation.

• Damage to these areas leads to various agnosias:

• Prosopagnosia: Inability to recognize faces.

• Achromatopsia: Loss of color perception.

• Akinetopsia: Impaired motion perception.

• Optic Ataxia: Difficulty reaching for objects due to dorsal stream damage.

Retinotopic Mapping

• The organization of visual information in the brain is topographically mapped:

• The left visual field is processed in the right hemisphere and vice versa.

• Information from the upper visual field projects to areas below the calcarine sulcus and vice versa for the lower field.

• Foveal representation occupies a disproportionately large area of the visual cortex, emphasizing its importance for visual acuity.

Eye Movement and Visual Tracking

• Effective reading often entails smooth eye movements, and individuals with dyslexia may exhibit more regressive eye movements or skips during reading, indicating processing differences in visual tracking.

Key Terms to Remember:

• Achromatopsia: Color blindness from V4 damage.

• Akinetopsia: Lack of motion perception due to V5 damage.

• Prosopagnosia: Face recognition deficit due to fusiform face area damage.

• Optic Ataxia: Inability to visually guide movements to objects.