Vision

Question 1

light sources

Answer 1

1. sunlight is filtered through the atmosphere and reflected from surfaces
2. light is electromagnetic energy that has properties of waves as well as charged particles
3. differs in intensity and wavelength

Question 2

humans and animals have image forming eyes

Answer 2

1. eyes come in many forms
2. advanced type of eyes have evolved several times in the animal kingdom
3. fossil records of image forming eyes date back to cambrian explosion
4. faster movement and navigation in animals required better vision which selected for eye types with higher spatial resolution
5. more neural resources are required to process a larger amount of info in image forming eyes

Question 3

large sized eyes and brain have capacity to process more visual information

Answer 3

1. visual field - area of space in which the eye sees its surroundings
2. retinal projection - small inverted 2D image that is distorted by the curvature of the eye
3. perceived image - 3D, large, upright , stable, non distorted, colourful
4. conscious vision - in human only with intact retina, thalamus and primary visual cortex

Question 4

how to see and be active during both day and night

Answer 4

1. many vertebrates have a duplex retina
2. cones have high sensitivity thresholds, therefore respond to bright light
3. rods have low sensitivity thresholds, therefore respond to low light
4. circuitry in duplex retina contains different types of visual interneurons for switching between day and night vision
5. sensory adaptation - during day or night, when light changes, sensitivity thresholds increase or decrease over time in cones or rods, respectively, this maximises contrast coding for better vision within the prevailing light range

Question 5

coping with changing light levels and wavelengths

Answer 5

1. rods and cones differ in morphology, sensitivity thresholds and wavelength selectivity
2. three functional class of cones (S, M, L)
3. cone opsins differ in their wavelength specific affinity to absorb light, only one opsin type is expressed per cone in the human retina
4. opsin - light sensitive protein (G protein coupled receptor molecule) in membrane of photoreceptors which is bound to the chromophore retina (needed for transduction)
5. one functional class of rods - all rods express the same type of opsin (RH1 or rhodopsin)
6. cone circuitry connects to colour coding pathways, whereas rods do not

Question 6

central fovea is active during the day and in bright light

Answer 6

1. acuity - ability to resolve spatial details, is proportional to the density of receptor cells
2. acuity of vision is highest in fovea and decreases towards the periphery of the retina
3. central fovea only contains cones
4. at night, high acuity is sacrificed for sensitivity and it is more advantageous to have no rods in the fovea

Question 7

impressionist art movement

Answer 7

1. impressionism - artists captured perceptual qualities of light, colour and atmosphere reflecting, new colour technologies, materials and dyes available
2. at the same time scientists discover principles of physics and perception of light
3. psychology emerges as scientific discipline studying visual perception and consciousness as well as emotion and memory
4. art and science influence each others explorations and development
5. cataract - clouding of lens in the eye - frequent but well treatable disease, monet had cataract

Question 8

why do we see what we see

Answer 8

1. we sometimes notice discrepancies between reality and perception
2. not a failure of sense or brain
3. the sensory systems and brain resolve ambiguities in the sensory environment
4. brain saves energy and number of neurons by remembering and predicting, depending on the environment, context and task

Question 9

first steps of processing in the retina of the eye

Answer 9

1. serial connections of visual pathway start in the retina - photoreceptors to bipolar cells, signals transmitted as graded potentials, bipolar to ganglion cells, long axons of ganglion cells form the optic nerve that transmits action potentials to the thalamus and other brain areas
2. cross connections between retinal layers - horizontal cells (inputs from photoreceptors and projections to bipolar cells), amacrine cells (inputs from bipolar cells and project to ganglion cells)
3. human retina contains approx. 100 million rods and 4 million cones and only 1 million ganglion cells

Question 10

visual pathways

Answer 10

1. geniculate-striate visual pathway - required for conscious vision in humans
2. retina - Lateral geniculate nucleus of the thalamus - V1 - areas of higher visual cortex (v1 required for conscious visual experiences)
3. extrageniculate pathways

Question 11

spatial layouts of projections from retinal ganglion cells

Answer 11

1. retinal ganglion cells project retinotopically to each layer of the LGN
2. right and left eye projections are also segregated in the LGN

Question 12

why do humans move their eyes

Answer 12

1. saccades - jumps, and fixations -stops
2. direct fovea to collect information about the visual scene
3. the field of view is defined by the position and orientation of the eyeball, head and body
4. 2-3 saccades per second
5. task influence eye movement patterns
6. automatic control of eye movements comes from superior colliculus
7. conscious control of eye movements come from the cortical frontal eye fields

Question 13

eye movements in everyday behaviour

Answer 13

saccades - move the eye very quickly to a new position between periods of gaze stabilisation (fixations) in order to scan the scene across the entire field of view

Question 14

atypical eye movements in dyslexia

Answer 14

1. difficulties in reading words, sentences, text
2. longer durations of fixations and shorted saccaded, more fixations during reading
3. shorter visual attention span impacts on eye movement patterns

Question 15

identifying spatial relationships and properties of objects

Answer 15

1. without context cues, we perceive the physical reflectance of the surfaces which carries little information
2. edges and shadows provide context information about the spatial structure of objects or spatial relationships between objects

Question 16

smart computations in complex vertebrate retina

Answer 16

1. functional classes of cells in the retina - 4 types of photoreceptors (3 cone types + rods), 50-70 types of horizontal, bipolar and amacrine cells, 20-30 types of ganglion cells
2. first stages of visual processing with inhibitory and excitatory synapses in neural circuits of retina
3. edge detection in visual scenes
4. edge enhancement in patterns
5. filtering of spatial, wavelength, movement and directional information

Question 17

receptive fields of bipolar and ganglion cells in the retina

Answer 17

1. convergence in the fovea (1 cone to 1 bipolar), periphery of the retina (many cones to 1 bipolar, many bipolar to 1 ganglion)
2. acuity is high in fovea (low convergence) and low in periphery of the visual field (high convergence)
3. cones that converge on a bipolar cell form the bipolar cell’s receptive field
4. similarly the receptive field of a ganglion cell is formed by all converging bipolar cells
5. many types of receptive fields

Question 18

signals of on/off cells change with ratio of light to dark

Answer 18

1. whilst the on centre bipolar cell depolarises, the on centre ganglion cell responds by increasing its spike rate
2. whilst the off centre bipolar cell hyperpolarises, the off centre ganglion cell responds by decreasing its spike rate
3. intermediate graded potential (bipolar cell) or spike frequency (ganglion cell) when illuminated with a uniform light stimulus

Question 19

filter mechanisms in the retina

Answer 19

1. filter mechanisms are neural circuits that combine excitatory and inhibitory synapses
2. bipolar and ganglion cells with on-centre/off-surround receptive field and vice versa
3. objects can be dark against a bright background or bright against a dark background

Question 20

columnar structure of V1

Answer 20

1. in addition to six horizontal layers, neurons in V1 are further segregated into functionally distinct hypercolumns
2. hypercolumn is composed by one left eye and one right eye ocular dominance column, several orientation columns containing simple and complex cells that respond to orientation of shapes, such as bar, blobs are structure in layer 2-3 of the v1 and are involved in colour vision
3. retinotopic organisation - the spatial mapping arising from the projection of the image onto the retina is preserved also in the v1

Question 21

responses of neurons in the orientation columns of v1

Answer 21

1. when recording from neurons of a particular orientation column in v1, these neurons respond to the orientation of a bar stimulus only within a small part of their receptive field
2. different to the retinal ganglion cells, these neurons fire at the maximal spike rate when a bar stimulus shows their preferred orientation
3. other cortical cells in v1 respond with the maximal spike rate to a preferred direction of motion of bars or patterns

Question 22

functions of simple and complex cells

Answer 22

1. analysis of contours and boundaries analysis of objects
2. shape and positional invariance
3. contour enhancement for object identification
4. v1 is fundamentally important for conscious vision and perception

Question 23

unconscious vision in blind humans

Answer 23

1. damage to v1 causes cortical blindness, the loss of conscious vision
2. patients are able to perform visually-guided behaviours like grasping or pointing to the location of objects or avoiding obstacles at a level above chance, this is blindsight

Question 24

v4 neurons respond to more complex stimuli

Answer 24

1. more complex compared to v1 and v2
2. strong responses in the anterior area of the inferior temporal cortex

Question 25

object recognition

Answer 25

1. discrimination 2. recognition of objects 3. categorisation 4. ventral cortical stream - critical for object recognition

Question 26

two visual streams in the cortex of primate/human brain

Answer 26

1. ventral stream - making sense of the world, v4 2. dorsal stream - interacting with world, v5 3. guiding hand movements requires two processes, deciding which object to interact with and doing s skillfully, these processes require different types of information from both the dorsal and ventral streams

Question 27

parallel visual streams and cross connections

Answer 27

pathways that bypass v1 has been accounted to mediate blindsight and residual capabilities for visual discrimination to blind people and monkeys

Question 28

subconscious vision and emotions

Answer 28

1. 5c mediated pathways are interconnected with amygdala 2. rapid processing of emotional information, in particular for salient stimuli 3. short cut to drive motor actions, such as fast orienting eye movements