Colour, depth, motion

What are three proposed functions of colour vision?

Frugivory, sexual signalling, and social signalling

How may colour vision help frugivory?

it helps distinguish ripe fruit from foliage

How may colour vision assist sexual signalling?

It helps detect colour-based mate cues

How is colour vision involved in social signalling?

Detecting emotional changes like blushing and anger

What is the difference between trichromats and dichromats?

Trichromats have three cone types; dichromats have two

What type of information does vision rely on?

Fluctuations in electromagnetic radiation

What is the relationship between wavelength and frequency?

They are inversely related

What part of electromagnetic radiation can humans see?

A limited visible spectrum

Why is the visible spectrum important biologically?

It overlaps with the peak intensity of sunlight reaching Earth

What determines visible light colour physically?

Wavelength

Is perceived colour soley determined by wavelength?

No

What is colour psychologically?

A percept produced by visible electromagnetic radiation

Why is colour considered a perceptual construct?

Because colour is created by the brain, not directly “in” wavelengths

Who proposed trichromatic theory?

Helmholtz

What did Helmholtz’s colour matching experiments show?

At least three wavelengths are needed to match colours

What condition must the three wavelengths satisfy in colour matching?

One wavelength cannot be recreated by mixing the other two

What physiological evidence supports trichromatic theory?

Three con types in the retina

What are the three cone types sensitive to?

Long, medium, and short wavelengths

Why is it misleading to call cones “red, green, blue” cones?

They respond to wavelengths, not perceptual colours themselves

What broader issue does colour naming connect to?

Language and colour perception

Who proposed opponent processing theory?

Hering

Why was trichromatic theory insufficient on its own?

It could not easily explain colour aftereffects or colour blindness patterns

What are the two opponent colour channels?

Red-green and blue-yellow

What additional channel did Hering propose?

A monochrome light-dark channel

Why don’t people typically have “reddish-green” perception?

Because colours are processed opponently

How does opponent processing explain afterimages?

Fatigue in one channel causes the other colour to dominate

Where does trichromatic processing occur?

Retina/ cones

Where do opponent processes occur?

LGN and later visual pathways

Why is depth perception important?

For reaching, grasping, catching, avoiding danger, and interacting with the world

What is surprising about depth perception?

A 3D world is perceived from 2D retinal images

What are the “four Fs” mentioned in relation to depth perception?

Flight, flight, food and reproduction

What is convergence?

Eye movements inward when focusing on nearby objects

How can accommodation provide depth information?

Lens focusing requires muscle changes that provide distance feedback

What limitation affects convergence and accommodation theories?

They only provide one depth estimate at a time

What is binocular overlap?

Overlapping visual fields from both eyes

What is stereoscopic vision/ stereopsis?

The ability to perceive depth and 3D structure by merging slightly different images from each eye

Why do predators tend to have forward-facing eyes?

Better stereoscopic depth perception

Why do prey animals often have side-facing eyes?

Wider panoramic vision for threat detection

What trade-off exists in eye placement?

Depth perception vs panoramic field of view

What is binocular disparity?

Differences between left and right eye images

Why can stereopsis not occur in the retina or LGN?

Left and right eye pathways remain separate there

What is the earliest cortical area where stereopsis could occur?

V1

Do V1 disparity signals automatically create depth perception?

No

What did Cumming & Parker (1997,2000) argue?

V1 signals disparity but not depth itself?

Which brain regions may create conscious depth perception?

Dorsal/parietal areas, possibly V2

Is stereopsis alone always useful?

No, it is limited without other cues

What did Smith & Scott-Samuel (1998) find about stereopsis alone?

Poor sensitivity to motion defined purely by stereopsis

What did Morgan’s blackberry-picking example show?

People with one eye patched had more cuts but picked similar amounts

What task is stereopsis especially useful for?

Fine manipulation like threading needles

Approximately what percentage of people have moderate-to-poor stereopsis?

32%

Why are two eyes more sensitive than one?

Better signal-to-noise ratio

What unusual function may two eyes provide according to Changizi & Shimojo (2008)?

Seeing through foreground clutter

What evolutionary explanation may account for two eyes

Bilateral symmetry

What is accommodation?

Lens focusing from different distance

What is occlusion?

One object blocking another

Why is occlusion a strong depth cue?

Blocked objects are perceived as father away

What limitation existed in medieval art?

Weal use of depth cues besides occlusion

What major advance did Renaissance art introduce?

Linear perspective

What is linear perspective?

Parallel lines appear to converge with distance

What are texture gradients?

Textures becoming denser/ smaller with distance

What is “height in image’ as a cue?

Objects higher relative to the horizon often appear father away

What is motion parallax?

Nearby objects move faster across the retina than distant ones during movement

In motion parallax, how do nearby objects appear to move?

Faster and opposite the observer’s movement

What is aerial perspective?

Distance objects appear bluish/ hazy because blue light scatters

Can the “light from above” assumption be altered?

Yes, through haptic learning

According to Sun & Perona (1998) is assumed lighting exactly vertical?

No, slightly offset

What happens when cast shadows are removed from moving objects?

Motion interpretation changes dramatically

What is forced perspective?

Manipulating viewpoint to distort perceived size/ depth

Why does forced perspective only work from certain viewpoints?

The illusion depends on precise geometric alignment

What is the Ames room illusion?

A distorted room appearing normal from one viewpoint

What do impossible figures demonstrate?

Limits and assumptions of visual interpretation

What is Sugihara famous for?

Building physical objects that appear impossible from specific viewpoints

What happens when Sugihara objects rotate?

Perception suddenly flips into the real structure

Why is motion perception important?

Important things and threats move

Why is change fundamental to consciousness?

Without change, time perception loses meanining

How can motion be detected neurally?

By delaying one signal and comparing it with another

What condition makes a motion detector neuron fire?

Simultaneous arrival of delated and direct inputs

What is motion opponency?

Comparing neurons tuned to opposite motion directions

Why is motion opponency useful?

It sharpens direction signals

What does microstimulation of MT do?

Alters motion perception

What did Tootell et al (1995) link V5 to?

Motion aftereffects

What is the aperture problem?

Local motion signals are ambiguous within limited receptive fields

What is optic flow?

Global movement patterns across the visual field during movement

Which brain areas process optic flow?

MST, V6, VIP and related dorsal areas

What is vection?

Illusory self-motion caused by visual movement