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What is the function of the retina?

The retina converts light energy into neural signals that the brain can interpret as vision.

What cells are responsible for detecting light in the retina?

Rods and cones (the photoreceptors).

What do rods detect?

Low-light (dim) conditions; they are responsible for black-and-white vision.

What do cones detect?

Color and fine detail; they function best in bright light.

After the photoreceptors are activated, which cells are next in the visual pathway?

The bipolar cells — they receive signals from rods and cones.

What happens first when light enters the eye?

Light triggers a photochemical reaction in rods and cones at the back of the retina.

What do ganglion cells do?

They receive input from bipolar cells and send visual information through their axons, which form the optic nerve.

What is the optic nerve?

A bundle of axons from ganglion cells that transmits visual signals to the visual cortex in the occipital lobe.

Where in the brain does visual processing occur?

The primary visual cortex (V1) in the occipital lobe.

What is the correct sequence of visual processing in the retina?

Rods/Cones → Bipolar Cells → Ganglion Cells → Optic Nerve → Visual Cortex

What are the two types of photoreceptors in the retina?

Rods and cones

How many cones are in the human retina?

6 million

How many rods are in the human retina?

120 million

Where are cones mostly located?

Center of the retina (fovea)

Where are rods mostly located?

Periphery of the retina (outside the fovea)

Which photoreceptor is more sensitive in dim light?

rods

Which photoreceptor works best in bright light?

Cones

Which photoreceptor detects color?

Cones

Which photoreceptor does not detect color?

Rods

Which photoreceptor is detail-sensitive (sharp vision)?

Cones

Which photoreceptor is not detail-sensitive (blurry edges)?

rrods

Why is the fovea important for vision?

It’s packed with cones → gives sharp, color vision in the center of your view

Why is peripheral vision better in dim light?

It has lots of rods → very sensitive to low light, detects movement

What is the blind spot in the eye?

The blind spot is the place on the retina where the optic nerve exits the eye, and there are no photoreceptors (rods or cones) there, so no light is detected.

Which side of the retina is the nasal side?

The nasal side is the part of the retina closest to the nose.

Which side of the retina is the temporal side?

The temporal side is the part of the retina closest to the temples/ears.

How do blind spots relate to the temporal and nasal sides?

The blind spot is located on the nasal side of each retina.

What are retinal ganglion cells (RGCs)?

Neurons in the retina that receive input from rods and cones (via bipolar cells) and send visual information to the brain through the optic nerve.

What is a ganglion cell’s receptive field?

The small patch of retina that a ganglion cell “monitors,” including a center and a surround.

How do ganglion cells encode light intensity?

By changing their firing rate: more light → higher or lower firing depending on the cell type (on-center or off-center).

What is an on-center receptive field?

Light in the center increases firing (activates the cell), light in the surround decreases firing (inhibits the cell).

What is an off-center receptive field?

Light in the center decreases firing (inhibits the cell), light in the surround increases firing (activates the cell).

Does the “center” of a receptive field mean the fovea?

No — it’s just the middle of that ganglion cell’s specific receptive field, which could be anywhere on the retina.

Why do ganglion cells have on/off-center receptive fields?

To detect contrast, edges, and patterns, not just absolute brightness.

Are both on-center and off-center ganglion cells present for the same patch of retina?

Yes — both types exist, but they respond differently to the same light pattern.

What did Hubel & Wiesel discover in their visual cortex experiments?

Neurons respond to specific features like orientation, edges, and movement.

What does a simple cell in V1 respond to?

A line or bar of a specific orientation in a specific location.

What does a complex cell in V1 & V2 respond to?

A line of a specific orientation anywhere in its receptive field, often moving.

What does a hypercomplex (end-stopped) cell respond to?

Lines or edges of specific length or corners/angles; stops firing if too long or shape doesn’t match.

How does a simple cell respond to stimuli?

Strongest firing if stimulus matches preferred orientation/location, weaker firing if partial match, no response if it doesn’t match.

What are bar and edge detectors?

Neurons in the visual cortex (V1/V2) that respond strongly to edges or bars of light with specific orientation, position, and width.

Are bar and edge detectors real cells?

Yes — they are neurons, just like ganglion cells, but located in the visual cortex, not the retina.

How do simple cells detect bars/edges?

They combine input from many ganglion cells aligned in a line to detect a specific orientation in a specific location.

How do complex and hypercomplex cells detect features?

• Complex cells: detect bars/edges anywhere in a larger receptive field, often moving

• Hypercomplex (end-stopped) cells: detect lines of specific length or corners/angles

What is the connection between ganglion cells and bar/edge detectors?

Ganglion cells detect local contrast, and their outputs are combined in V1 cells to detect lines, edges, motion, and shape in the visual scene.

How is visual information processed from the retina to perception?

• Ganglion cells (retina): detect local contrast (light/dark differences)

• Simple cells (V1): detect edges or bars of specific orientation and location using ganglion cell inputs

• Complex cells (V1/V2): detect edges/bars anywhere in receptive field, often sensitive to motion

• Hypercomplex cells (V1/V2): detect lines of specific length, corners, or angles

• Brain integrates these signals → full visual perception

• 💡 Analogy: Like a factory assembly line: raw materials (ganglion) → first assembly (simple) → advanced assembly (complex/hypercomplex) → finished product (perception).

How is the cingulate cortex analogous to the occipital → temporal/parietal pathways?

• Cingulate cortex: integrates sensory + emotional info and sends it to the forebrain for critical thinking.

• Occipital → temporal/parietal: occipital lobe detects raw visual features; temporal lobe recognizes “what” objects are; parietal lobe detects “where” objects are.

• Analogy: Both show hierarchical processing—basic info is processed in early regions, then sent to higher regions for interpretation and action.

What is the ventral “what” pathway?

A visual pathway from the occipital lobe → temporal lobe that identifies what an object is, including form, features, and object identity.

What is the dorsal “where” pathway?

A visual pathway from the occipital lobe → parietal lobe that processes motion and spatial location, helping to locate objects in space and track their movement.

What types of processing does the ventral pathway handle?

Form discrimination, object identification, and recognition of detailed features.

What types of processing does the dorsal pathway handle?

Motion detection, spatial location, and guiding actions based on where objects are.

Why do visual signals go from occipital lobe to other lobes?

The occipital lobe detects basic features (edges, lines, motion). Higher lobes integrate these features:

• Temporal lobe → recognize objects (“what”)

• Parietal lobe → locate objects (“where”)

How can the ventral/dorsal pathways be compared to a factory?

Occipital lobe = raw materials (edges, lines, motion) → Temporal lobe = object ID department (“what”) → Parietal lobe = navigation/interaction department (“where”).

What happens if the ventral “what” pathway is damaged?

Visual object agnosia — the person can see objects but cannot recognize or identify them visually.

Can a person with ventral pathway damage recognize objects by other senses?

Yes — they may recognize objects by touch or sound, just not visually.

What happens if the dorsal “where” pathway is damaged?

Spatial agnosia / optic ataxia — the person can recognize objects but cannot locate or interact with them properly in space.

Examples of dorsal pathway damage symptoms?

• Trouble reaching for objects accurately

• Difficulty judging distances or motion

• Problems navigating around obstacles

Key difference between ventral and dorsal pathway damage?

• Ventral (“what”) damage: object recognition impaired

• Dorsal (“where”) damage: spatial location and motion perception impaired

How can you remember the difference between ventral and dorsal pathway damage?

• Ventral = “What department” → broken → see objects but don’t know what they are

• Dorsal = “Where department” → broken → know what objects are but can’t locate or interact with them

What features are visual pathway cells sensitive to?

Cells in the ventral (“what”) and dorsal (“where”) pathways can be sensitive to color, movement, and orientation.

How are visual features represented in the brain?

Features are analyzed independently and mapped in feature maps for processing.

What is figure-ground segregation?

The process of distinguishing the object of focus (figure) from the background (ground) in a visual scene.

After figure-ground segregation, how does the brain perceive meaningful forms?

It organizes the figure using Gestalt principles, grouping features into a coherent whole.

What are some Gestalt principles of organization?

• Proximity: group items close together

• Similarity: group similar items

• Continuity: perceive continuous lines/shapes

• Closure: mentally fill in missing parts

What is the flow from feature detection to perception?

Feature-sensitive cells → feature maps → figure-ground segregation → Gestalt principles → perception of meaningful objects.