Perecption > Spatial Vision > Flashcards

Spatial Vision Flashcards

(56 cards)

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1
Q

What is the V1

A

Primary visual context, the first cortical stage of visual processing

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2
Q

How is the V1 organised

A

Retinotopic map of the visual field

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3
Q

What does the V1, Retinotopic map feature

A

Laminar structure, columnar functional arrangement, cortical magnification of the central visual lobe

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4
Q

Where is the V1 located

A

Occipital lobe

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5
Q

What does the V1 contain

A

Neurons organised by their receptive field to represent spatial, directional and ocular information

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6
Q

Retinotopic mapping in detail

A

Spatial map of the retina, neighbouring neurons repsond adjacent areas of the visual field, left to right and right to left.

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7
Q

What is cortical magnification

A

Significant portion of V1 (roughly half) dedicated to processing the central 10 degrees of the visual field, proving high acuity

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8
Q

What is the central 10 degrees of the visual field

A

Fovea

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9
Q

What does the peripheral regions do

A

Process anteriorly

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10
Q

What is the laminar structure

A

V1 - 6 layer neocortex, layer 4C receives the primary input from the LGN

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11
Q

What is the LGN

A

Lateral geniculate Nucleus

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12
Q

Retinotopy

A

Neighbour relationships in retina are retained in the cortical map

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13
Q

What is the organisation of the V1

A

Columns orientated, within 0.5mm, ocular dominance bands

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14
Q

What is a hyper column

A

Neurons are arranged in columns that repsond to specific line orientations, forming “pinwheels”

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15
Q

What is ocular dominance columns

A

Columns segregated by input from left to right eye, particular in layer 4

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16
Q

Blobs

A

Colour sensitive areas are known as blobs and often located in layers 2 and 3

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17
Q

What are the two neuron classifications

A

Simple cells and complex cells which process features like orientation and motion

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18
Q

What is simple cells

A

Separate on and off receptive fields

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19
Q

What is complex cells

A

Spatially superimposed on/off region

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20
Q

V1 Cortical connections

A

Heavily interconnected, local horizontals connection in upper layers for processing the local visual surround and feedback from high visual ares (V2, V3, MT) to layers 1 to 6

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21
Q

What is a sine wave or sinusoid wave

A

Continuous smooth, periodic oscillation that represents a single frequency with no harmonics

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22
Q

What is the characteristics and properties of a sin wave

A

Shape of sine function, including cosine waves

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23
Q

Frequency

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A

Higher spatial frequencies represent finer details and lower frequencies represent coarse, overall shapes

24
Q

Orientation of a sine wave

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A

Refers to the angle of the gratings stripes.

Human visual system exhibits better sensitivity (lower thresholds) for horizontal and vertical orientations compared to oblique ones,

25
What is the oblique effect
Oblique orientations aren’t exhibited better than sensitive horizontal and vertical ones
26
Gratings
Periodic patterns of light and dark bars with luminance that varies sinusoidally across space, creating smooth, blurry and gradual transitions rather than sharpe edges
27
Grating characteristics
Number of cycles per degrees of visual angle. Low frequency = lower, wider High frequency = higher, narrow Michelson contrasts 0-1 Angle of grating meausres in vertical degrees
28
Visual angel
The visual angel tells us the size of the retinal image (Given a certain object size at a certain distance)
29
High and low frequencies
Spatial frequency due=fines the rate of intensity change within an image, HSF represents fines details, sharps edges and rapid changes LSF represents broad shapes, smooth gradients and global structure
30
Why sine wave gratings
Every image can be broke down into sine wave compoents Fourier analysis Visual system conducts the equivalent of a local Fourier analysis
31
What is a Fourier analysis
Mathematical technique that breaks down complex repeats of signals or functions into a sum of simpler sine and cosine waves, Translates data Fromm the time or spatial domain into how frequency domain
32
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Fourier analysis purpose
Identify and analyse, manipulate the underlying frequencies, amplitudes and phases within a signal
34
Fourier analysis components
Identifying the spectrum of a signal to reveal dominant frequency
35
FFT
Fast Fourier transform - crucial algorithm that allows for faster computed calculations of teh discrete Fourier transform
36
Local Fourier analysis hypercolumns
Contain neurons turned into different orientations, spatial frequencies All the neurons analyse the same patch of visual space Together, they extract spatial frequencies and orientations in their local patch they conduct a local Fourier analysis.
37
Adaption
Both a method and process in the visual system
38
Adaption method
State at the same stimulus for a long time
39
Process adaption
Consequence of long exposure those neurons that are turned to the stimulus property decreases their sensitivity
40
Spatial frequency channels early vision
Use multiple overlapping channels tuned to specific frequencies, analogous to a Fourier transform Unlike global Fourier analysis, neurons analysing small restricted and orientated patched of an image
41
Tilt after effect
Visual illusion where prolonged viewing of a tilted orientated pattern (adapter) causes subsequent, upright, different orientated patterns to appear rostered iin the opposite direction
42
Tilt aftereffect percpetual phenomenon
Neurons in the primary visual correct adapt to the inital tilt, shifting to their preferred orientations
43
Tilt mechanism
Neural adaption, neurons strongly activated by intial stimulus become suppressed causing a shift in the percieved orientations Stronger within 10-20 Illusion is short lived, decaying over time as the visual system returns to a neutral state
44
Receptive field
Small, topographically organised regions in the visual field that process visual features like edge orientation, direction and spatial frequency
45
Population code of tilt effect
Shift in the percieved orientation of a srtimulus due to contextual interactions in the V1, typically modeled as a repulsive bias or an aftereffect Driven by centre surround inhibition and adaption-induced shifts in neuronal tuning curves
46
Repulsive
15, differences Typically occurred when a center stimulus is flanked by a slightly differently orientated surround, causing the perceived angle to shift away from the induce
47
Attractive
Weaker effecr where the perceived angel shifts close to the induce, often occurring at larger angular difference
48
Adaption TAE
Prolonged viewing of oriented stimulus causes fatigue, suppression fo neurons tuned to that orientation lead to shift in the population response in subsequent perception
49
Contrast sensitivity
Meausres the minimum contrast needed to detect an object
50
Spatial scale
Size of details in an image, ranging from large shapes to fine details
51
Sensitivity
Our visual system differs for different spatial scales
52
CSF
Meausres the visual systems ability to detect subtle difference in luminance (shades) across varying spatial frequencies (object sizes)
53
CSF define
The inverse of the contrast threshold needed to detect a stimulus Represents a band-pass curve, meaning human vision is most sensitive to intermediate spatial frequencies, less sensitive to very large or very small fine-detailed objects
54
What is the significance in clinical vision
More informative than aucity, high contrast aucity only measures one point of the function, helps detect and monitor disease like glaucoma
55
What produces the CSF
Population of neuron tuned to similar spatial frequency forms, a spatial frequency chart
56
Independence of spatial frequency channels
Indepedently operating parallel mechanism in the visual system, each tuned to a narrow range of spatial frequencies. The channels are separate from orientation mechanisms, allow the visual system to process fine details and coarse chapels through broader scales, exhibit complex interactions
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