0010 Ch 5 Gaps (1/2)

What does the textbook's Fig. 5.3 (incomplete letters embedded in words) demonstrate?

The same central shape is read as different letters depending on word context — a top-down effect; it also explains why proofreading your own writing is hard

Which sense bypasses the thalamus on its way to the cortex?

Smell (olfaction) — its input goes directly to cortex, while all other senses relay through the thalamus first

How are qualitative vs quantitative sensory differences coded neurally?

Qualitative differences (tuba vs flute; salty vs sweet) are coded by which receptors/neurons respond; quantitative differences (loudness, brightness) are coded by firing rate or number of neurons firing

Who founded psychophysics, and when?

Ernst Weber and Gustav Fechner, in the 19th century

What is sensory adaptation, and what happens when a constant stimulus stops?

Sensitivity decreases to a constant stimulus (e.g., a friend's cat-litter smell fades); sensory systems respond strongly when a continuous stimulus stops

What is the McGurk effect?

An auditory illusion (McGurk & MacDonald, 1976): conflicting visual cues change what you hear — hearing "BA" while seeing a mouth shape for "DA" or "VA" alters the perceived sound

What did Ramachandran & Hubbard (2001) propose about synesthesia?

Color/number synesthesia arises because the color-vision brain area lies near the number area, so one may adopt the other's role; synesthetes viewing black numbers showed color-area activity absent in controls

Give the textbook's multisensory-integration example and what an expectation violation shows

An orange is perceived via vision + touch + smell + taste (+ hearing); expecting orange but tasting lime produces a strong reaction — perception integrates the senses into one stable representation

What did James Enns (2005) claim about seeing?

Very little of seeing happens in the eyes — most is constructive processing across the brain; visual-cortex damage impairs vision even with functional eyes

Which eye structure does most of the focusing of light?

The cornea (thick transparent outer layer); the lens only fine-tunes focus

What is presbyopia?

The lens hardens with age (common after 40), making near focus difficult — corrected with reading glasses

How many rods vs cones are in each retina?

~120 million rods vs ~6 million cones

Why does a dim star vanish when you stare directly at it?

There are no rods in the fovea, so dim (rod-detected) objects disappear under direct gaze but reappear off to the side

Which are the first neurons in the visual pathway to fire action potentials, and why not the photoreceptors?

Retinal ganglion cells; rods and cones don't fire APs themselves — light splits their photopigments, changing membrane potential, which triggers APs in downstream neurons

What happens at the blind spot, and how large is it?

The optic nerve exits where there are no rods or cones; the brain fills the gap automatically (roughly fist-sized at arm's length)

What crosses at the optic chiasm, and what is the result?

Axons from the nasal side of each retina cross, so the left visual space projects to the right hemisphere and vice versa

Is color a property of objects?

No — it is a product of the visual system; objects look colored because of the wavelengths they reflect

What is the visible light range?

~400–700 nm

Name the three cone types and their peak sensitivities

S (short/blue–violet), M (medium/yellow–green), L (long/red–orange)

Why does mixing red and green light look yellow?

Yellow light stimulates L and M cones about equally (barely S); red + green light produces the same L/M pattern, so the brain can't tell the difference (trichromatic theory)

What causes red–green vs blue–yellow color blindness?

Red–green: missing medium- or long-wavelength photopigment; blue–yellow: missing short-wavelength photopigment; genetic — ~8% of males, <1% of females