Lecture 3: Vision - From retina to cortex

Question 1

What does the “problem of vision” refer to?

Answer 1

The inherent ambiguity in visual signals received by our eyes, e.g. how a shape can appear differently based on perspective.

Question 2

What happens to visual information as it travels from the retina to the cortex?

Answer 2

The eye processes images, passing signals through the retina, then the lateral geniculate nucleus (LGN), and finally to the cortex where perception occurs

Question 3

What is bi-stable perception in the “Spinning Dancer” illusion by Nobuyuki Kayahara (2003)?

Answer 3

A phenomenon where individuals perceive the dancer spinning in different directions due to a lack of depth cues.

Question 4

How does the “Spinning Dancer” illustrate ambiguity in perception?

Answer 4

People interpret which leg the dancer is standing on differently, highlighting individual differences in perception.

Question 5

How does perspective influence shape perception in visual processing?

Answer 5

Different perspectives lead to different shapes being observed, showcasing the ambiguity of visual information.

Question 6

What are depth cues, and why are they important in visual perception?

Answer 6

Depth cues provide spatial information that helps resolve ambiguity; their absence, as in the “Spinning Dancer,” leads to multiple interpretations.

Question 7

What is the main role of the retina in vision?

Answer 7

The retina captures the image of the world and projects it onto the retina, bouncing the information back through the optic nerve.

Question 8

What is the function of the iris?

Answer 8

The iris adjusts the size of the pupil to regulate the amount of light entering the eye.

Question 9

What are photoreceptors, and what types exist?

Answer 9

Photoreceptors are cells sensitive to light, divided into rods (dim light) and cones (daytime vision, colour sensitivity).

Question 10

What is rhodopsin, and where is it found?

Answer 10

Rhodopsin is a photopigment found in rods, enabling them to respond to dim light.

Question 11

What is the primary role of cones?

Answer 11

Cones detect color through three types of photopigments sensitive to different wavebands (long, medium, short).

Question 12

What do retinal ganglion cells do?

Answer 12

They perform preprocessing and transmit visual signals from the retina to the brain.

Question 13

Differentiate between parasol and midget ganglion cells.

Answer 13

Parasol cells have large receptive fields (magnocellular), and midget cells have small receptive fields (parvocellular).

Question 14

What is the receptive field in vision?

Answer 14

It is the area of the retina from which a ganglion cell receives input.

Question 15

How do on-center and off-surround retinal ganglion cells respond to light?

Answer 15

They increase activity when light fills their center and decrease activity when light fills the surround.

Question 16

Who identified lateral inhibition in ganglion cells?

Answer 16

Kuffler (1953).

Question 17

What is the significance of lateral inhibition?

Answer 17

It enhances edge detection by increasing contrast in the visual field.

Question 18

What is the primary role of the fovea in vision?

Answer 18

The fovea is responsible for high-definition vision as it is densely packed with cones.

Question 19

How do retinal ganglion cells help process visual information?

Answer 19

They filter out gradual changes and emphasize sharp edges, improving visual clarity.

Question 20

What is the function of the lens?

Answer 20

The lens focuses light onto the retina and adjusts shape for accommodation.

Question 21

How does light reach photoreceptors in the retina?

Answer 21

Light passes through the retina layers, reaching the photoreceptors at the back, which need nutrients from the lower layers.

Question 22

What role does the lateral geniculate nucleus (LGN) play in vision?

Answer 22

It relays visual information from the retina to the primary visual cortex (V1)

Question 23

What is the significance of the visual cortex (V1)?

Answer 23

It processes basic visual elements like orientation, motion, and spatial frequency.

Question 24

How does the visual system deal with ambiguity in visual signals?

Answer 24

By combining cues and prior knowledge to interpret shapes and perspectives.

Question 25

What causes the ambiguity in the “Spinning Dancer” illusion?

Answer 25

Lack of depth cues results in bi-stable perception, making the dancer appear to spin in either direction (Kayahara, 2003).

Question 26

What is the difference between the parasol (magnocellular) and midget (parvocellular) pathways?

Answer 26

The magnocellular pathway processes motion and large-scale contrast, while the parvocellular pathway handles detail and color.

Question 27

How is the LGN organized, and what are its key features?

Answer 27

The LGN contains folded layers that organise signals from the three pathways (parvocellular, magnocellular, koniocellular). Each layer processes information from different subsystems of vision.

Question 28

What are the three pathways in the LGN, and what do they process?

Answer 28

Parasol (Magnocellular) pathway: Processes motion and low-light signals.
Midget (Parvocellular) pathway: Processes fine details and color.
Koniocellular pathway: Specializes in color contrast, particularly blue-yellow.

Question 29

What kind of stimuli might be used to study LGN pathways experimentally?

Answer 29

~Parasol (Magnocellular) pathway: Gratings with movement, drifting, or flickering patterns.
~Midget (Parvocellular) pathway: High-resolution images or colour-focused patterns like lime-violet vertical gratings.
~Koniocellular pathway: Stimuli emphasizing blue-yellow contrast, e.g., BBC Planet Earth visual scenes.

Question 30

How does the LGN contribute to visual perception?

Answer 30

The LGN filters visual input by separating it into pathways for motion, detail, and colour. This organised processing ensures efficient transmission of relevant information to the primary visual cortex, facilitating detailed and dynamic visual perception.

Question 31

What is the Primary Visual Cortex (V1)?

Answer 31

V1 is the first cortical region to process visual information, receiving signals from the LGN. It handles essential tasks like motion, edges, and color integration.

Question 32

How much of the brain’s cortex is dedicated to vision?

Answer 32

Over 50% of the cortex is involved in processing visual information, making vision a dominant sense.

Question 33

What is Retinotopy?

Answer 33

The mapping of the visual field onto the cortex, with adjacent points on the retina corresponding to adjacent areas in V1.
Photoreceptors from the fovea connect to V1, representing every point in the visual field.

Question 34

What did Hubel and Wiesel study?

Answer 34

They investigated how the visual cortex responds to stimuli using cats and discovered that cortical cells respond specifically to edges and bars of light with particular orientations.

Question 35

What was a key finding of Hubel and Wiesel’s experiment?

Answer 35

Cells in the visual cortex do not respond to dots but to lines or edges.
Vertical lines trigger stronger responses compared to other orientations.

Question 36

Why is the Primary Visual Cortex (V1) critical for vision?

Answer 36

It integrates signals from the LGN, processing features like motion, orientation, and spatial detail to create a coherent visual experience.

Question 37

What is unique about the LGN’s organization?

Answer 37

It has distinct layers that separate and process signals from each visual pathway, maintaining their specialised functions.

Question 38

How do visual pathways interact in V1?

Answer 38

Signals from the LGN pathways converge in V1, allowing for complex interpretations of visual stimuli such as colour, motion, and spatial relationships.

Question 39

What is intrinsic optical imaging, and what does it reveal about V1?

Answer 39

Intrinsic optical imaging is a technique used to visualize cortical activity Ohki et al. (2006). It reveals that cells in V1 respond to all types of orientations, showing a pinwheel arrangement characteristic of V1’s properties.

Question 40

What is the pinwheel arrangement, and where is it found?

Answer 40

A property of V1, revealed through imaging studies like those by Ohki et al. (2006), where cells responding to various orientations are organized in a circular pattern. This arrangement is a hallmark of orientation selectivity in the primary visual cortex.

Question 41

How do simple cells in V1 achieve orientation selectivity?

Answer 41

Simple cells in V1 achieve orientation selectivity based on the arrangement of inputs from LGN cells. This principle was first introduced by Hubel and Wiesel in their experiments on the visual cortex.

Question 42

What role does the arrangement of LGN cells play in V1 cell responses?

Answer 42

The arrangement of LGN cells determines the orientation selectivity of simple cells in V1. This was demonstrated by Hubel and Wiesel, showing that specific alignments of excitatory and inhibitory inputs create responses to particular orientations.

Question 43

What is the functional significance of orientation selectivity in V1?

Answer 43

Orientation selectivity in V1, as discovered by Hubel and Wiesel, allows the visual system to detect edges and shapes, contributing to the perception of objects in the environment.

Question 44

What experiment did Blakemore and Cooper (1970) conduct to study the role of development and critical periods?

Answer 44

They raised kittens in striped tubes with only vertical or horizontal stripes for 5 hours a day and examined their visual responses 5 months later.

Question 45

What were the findings of Blakemore and Cooper’s (1970) experiment on kittens?

Answer 45

Kittens showed no neuronal response in the visual cortex to orientations absent in their environment (e.g., vertical kittens didn’t respond to horizontal lines).

Question 46

What concept is demonstrated by the findings of Blakemore and Cooper’s (1970) study?

Answer 46

Neural plasticity within a critical period, highlighting “use it or lose it” as a principle of brain development.

Question 47

What is the critical period, as shown in Blakemore and Cooper’s (1970) study?

Answer 47

A time during development when the brain is highly sensitive to environmental input; after this period, the brain may not adapt to previously absent stimuli.

Question 48

What does the phrase “use it or lose it” mean in the context of neural plasticity?

Answer 48

It refers to the necessity of environmental stimulation for the development of certain neural pathways; without exposure, those pathways fail to develop.

Question 49

How does Blakemore and Cooper’s (1970) study relate to neural coding?

Answer 49

It demonstrates that the brain’s neural coding can be influenced by environmental exposure during the critical period of development.

Question 50

What are the two streams of processing beyond V1?

Answer 50

Ventral stream: “What” pathway, processes features like color and form to help identify objects.
Dorsal stream: “Where” pathway, processes spatial location and movement, connecting to the motor system.

Question 51

According to Ison & Quiroga (2008), how is visual information processed hierarchically in the brain?

Answer 51

Retina: Detects light and basic contrasts.
LGN (Lateral Geniculate Nucleus): Organizes and relays signals.
V1: Processes basic orientations.
V4: Handles color and intermediate complexity.
IT (Inferotemporal cortex): Processes complex shapes and faces.

Question 52

What did Suchow & Alvarez (2011) find about how color and motion are processed in the brain?

Answer 52

Ventral stream: Processes color information.
Dorsal stream: Processes motion information.

Question 53

How do the dorsal and ventral visual streams differ in their functional roles?

Answer 53

Dorsal stream: Encodes spatial location (“where”) and movement, projecting to motor areas.
Ventral stream: Encodes features like shape and color (“what”), crucial for object recognition.

Question 54

How do the dorsal and ventral streams integrate to help us interact with the environment?

Answer 54

Ventral stream: Identifies objects (e.g., recognizing a ball).
Dorsal stream: Tracks spatial location and movement (e.g., catching the ball).

Question 55

What type of specialized neuronal processing allows humans to detect faces so effectively?

Answer 55

Humans possess face-responsive neurons which are located in the inferior temporal cortex and the banks and walls of the superior temporal sulcus (STS), enabling efficient recognition even in complex or ambiguous visual scenes.

Question 56

What is facial pareidolia, and how does it demonstrate specialized face-processing neurons?

Answer 56

Facial pareidolia refers to seeing faces in inanimate objects or patterns. This phenomenon highlights the brain’s specialized neural pathways optimized for face recognition.

Question 57

Why is face detection considered a unique aspect of human visual processing?

Answer 57

Face detection is unique because it relies on highly specialized neural mechanisms, such as those in the fusiform face area (FFA), which are specifically tuned for identifying and distinguishing faces.