chapter 2,6 medium tf

Sensation & Perception

• Sensation: Effects of stimulus on sensory organs
• Perception: Interpretation of stimulus based on prior experience
• The brain actively constructs the visual representation of the world

From Eye to Brain

• Rod cells: Specialized for low intensity of light and movement
• Cone cells: Specialized for high intensity of light and color information
• Fovea: Entirely made of cones, responsible for visual acuity
• Blind spot: Where the optic nerve leaves the eye

Geniculostriate Pathway

• Optic nerve → Optic chiasm → Optic tract → Lateral Geniculate Nucleus (LGN) → Primary visual cortex (V1)

Primary Visual Cortex (V1)

• Located in the occipital lobe, responsible for visual processing
• V1 is the first stage of processing in the cortex
• Simple cells: Respond to particular orientation and single points of light
• Complex cells: Combination of simple cells, larger receptive fields, respond to movement of orientation, do not respond to single points of light
• Hypercomplex cells: Just outside V1, built from responses of complex cells, respond to orientation and length

Cortical & Non-Cortical Routes

• Geniculostriate pathway is the best understood and makes the largest contribution to human visual perception
• Other routes are evolutionary older
• Pathway to suprachiasmatic nucleus in the hypothalamus provides information about time of day
• Pathways via superior colliculus and inferior pulvinar are important for orienting stimuli

Problems with Primary Visual Cortex

• Retinotopic organization: Layout of the receptive fields of neurons in V1 reflect the spatial organization of the retina
• Hemianopia: Cortical blindness restricted to one half of the visual field
• Quadrantanopia: Cortical blindness restricted to a quarter of the visual field
• Scotoma: A small region of cortical blindness

Blindsight

• Inability to report perceiving visual stimulus even though performance suggests otherwise
• Case of DB: Reported not seeing stimuli but oriented his eyes correctly toward stimuli

Extrastriate Areas in Vision

• V4: Associated with color perception and color constancy
• Achromatopsia: A failure to perceive color due to damage to V4
• V5 (or MT): Associated with motion perception
• Akinetopsia: A failure to perceive visual motion due to damage to V5

Dual Stream Visual Processing

• No specific information provided

Object Recognition

• 1. Perception of basic elements (e.g., edges of various lengths, contrasts & orientations)
• 2. Grouping physical elements (depth cues and divide surfaces)
• 3. The viewer-centered description is then matched onto stored 3D descriptions of the structure of objects
• 4. Meaning is attributed to the stimulus

Agnosia

• Failure in object recognition
• Apperceptive agnosia: A failure to recognize objects due to a deficit at the level of object perception
• Associative agnosia: A failure to recognize objects due to a deficit at the level of semantic memory
• Case of HJA: Seeing the part but not the whole, impaired at deciding if objects are real or made up and naming objects

Categorical Perception

• Category specificity: The brain represents different categories in different ways (and/or different regions)
• Parahippocampal place area (PPA): Area of the brain that responds to scenes more than objects
• The extrastriate body area (EBA): Area of the brain that responds to the human body more than to faces, scenes or objects

Face Recognition

• Fusiform face area (FFA): An area in the inferior temporal lobes that responds more to faces than other visual objects
• Prosopagnosia: Inability to recognize previously familiar faces

Introducing the Brain

• Neurons are cells that make up the nervous system, consisting of a cell body (soma), dendrites, and axon.
• The cell body contains the nucleus and organelles.
• Dendrites receive information, while the axon sends information.

Neural Communication

• Terminal buttons of a neuron and dendrites of another neuron communicate through a small gap called a synapse.
• Presynaptic neuron is the information giver, while postsynaptic neuron is the information receiver.
• Action potential electrically charges the presynaptic neuron, inducing the release of informative chemicals called neurotransmitters.

Terms of Directional References

• Lateral: refers to the outer regions of the brain.
• Medial: refers to the central regions of the brain.

Gross Organization of the Brain

• Gray matter consists of cell bodies.
• White matter consists of axons and glia (support cells involved in tissue repair and myelin formation).

Cerebral Cortex

• Folded sheets of gray matter.
• Raised surfaces are called gyri (gyrus).
• Folds are called sulci (sulcus).
• The folded structure helps to increase area/volume ratio (efficiency in packaging of the brain).

4 Main Parts of the Cerebral Cortex

• No specific information provided about the 4 main parts.

Subcortex

• Lies under the white matter.
• Consists of a gray matter collection.
• Includes basal ganglia, limbic system, thalamus, and hypothalamus.

Basal Ganglia

• Responsible for motor control and skill learning.
• Disorders associated with poverty or excess of movement (e.g., Parkinson's and Huntington's).

Limbic System

• No specific information provided about the limbic system.

Diencephalon

• Includes thalamus and hypothalamus.

Midbrain and Hindbrain

• No specific information provided about midbrain and hindbrain.