PSY3108 exam content lec 1-11(midterm content)

Why does perception matter for cognition?

Cognitive performance correlates with perceptual performance (r = .4).

What does the moon illusion show?

That perception is not a perfectly veridical representation of the world.

Define “naïve realism.”

The idea that our senses give us a perfectly accurate picture of the world.

Why is naïve realism untenable, according to the slides?

Because perception uses heuristics, produces illusions, and does not give a perfect copy of reality.

Difference between a heuristic and an algorithm?

Algorithms require full information and give exact answers; heuristics use partial info, make assumptions, are fast, and can be wrong.

Why do our senses use heuristics rather than algorithms?

Because they must operate quickly with incomplete information.

Define naïve realism. Why is it wrong?

Belief senses reflect reality perfectly; wrong because perception is heuristic and can be inaccurate.

What are the two major types of methods in perception research?

Phenomenology and quantitative methods.

What questions does phenomenology answer?

“What are the interesting questions?” (big-picture observations).

What questions do quantitative methods answer?

“What are the detailed answers?” (precise measurements).

What is phenomenology?

Qualitative, naturalistic observation of perceptual phenomena.

What does phenomenology typically yield?

A verbal description of one’s observations (sometimes simple numbers).

What is the purpose of phenomenology in perception research?

It provides the first step — identifying the phenomenon and giving the “big picture.”

Why is phenomenology important before quantitative testing?

It helps identify interesting effects, illusions, or questions worth measuring in detail.

What classic example of phenomenological observation is given in the slides?

Jan Purkinje noticing his flower bed changed colour appearance from day to twilight.

What hypothesis did Purkinje’s observation lead to?

The hypothesis of two visual systems (rods vs. cones).

How does the Purkinje example show the role of phenomenology?

A simple personal observation led to major discoveries about rod and cone function.

Why is the Thatcher Illusion considered phenomenological?

It began as an interesting observation, then led to quantitative studies on face processing.

What is psychophysics?

The study of the relationship between physical reality (physics) and subjective perception (psycho).

What types of stimuli does psychophysics traditionally use?

Very simple, low-level stimuli that are easy to characterize.

What do threshold-seeking methods measure?

Physical quantities that represent limits of perceptual ability (thresholds).

What are examples of applied threshold-seeking methods from the slides?

Visual acuity tests, hearing tests, tactile acuity tests.

Why are threshold-seeking methods important in applied settings?

They test perceptual limits that matter for medical and professional evaluations.

According to the slides, what are two major quantitative approaches besides thresholds?

Threshold-seeking and magnitude estimation.

What physical property determines the colour we perceive?

Wavelength.

Does the perceived brightness of light depend on wavelength?

Yes — wavelengths have different perceived brightness even at equal energy.

What physical property determines perceived light intensity?

Amplitude.

Why is brightness perception not identical to physical intensity?

Because perception depends on wavelength and the visual system’s sensitivity, not only on physical energy.

What two parts of the eye refract light?

The cornea and the lens.

Which part of the eye is responsible for fine focusing?

The lens (via accommodation).

What is accommodation?

Changing the shape of the lens to focus at different distances.

Why does accommodation decline with age?

The lens becomes less flexible (presbyopia), reducing focusing ability.

What are the two major types of photoreceptors?

Rods and cones.

Which photoreceptor is used in low light?

Rods.

Which photoreceptor mediates colour vision?

Cones.

Where is the fovea located?

The center of the retina.

What type of photoreceptors are in the fovea?

Almost entirely cones.

What is found at the optic disc?

The blind spot (no photoreceptors).

Which photoreceptor type saturates at moderate light levels?

Rods.

Which photoreceptor gives high acuity?

Cones.

Why do cones provide higher spatial resolution than rods?

Cones have less convergence onto ganglion cells, preserving detail.

How does rod density vary across the retina?

Highest in the peripheral retina; absent at the fovea.

Where is cone density highest?

The fovea.

Why is peripheral vision better for detecting faint light?

The periphery has high rod density, and rods are more light-sensitive.

What cells do photoreceptors synapse onto?

Bipolar cells.

Bipolar cells synapse onto what next?

Ganglion cells.

Where do ganglion cell axons go?

They form the optic nerve.

Where do signals go after the optic nerve?

To the lateral geniculate nucleus (LGN) and then to the visual cortex.

What causes the blind spot?

Lack of photoreceptors where the optic nerve exits the eye.

Why don’t we normally notice the blind spot?

The brain fills it in using surrounding information.

What happens to visual sensitivity in the dark?

It increases (dark adaptation).

Which photoreceptor adapts more quickly to darkness?

Cones.

Why does the rod system take longer to adapt?

Rod photopigment regenerates more slowly.

What molecule absorbs light in rods?

Rhodopsin.

What happens when photopigment molecules absorb light?

They break apart (bleach).

What must happen for sensitivity to return?

Photopigment must regenerate.

What gives rods higher sensitivity?

Many rods converge onto fewer ganglion cells.

What gives cones higher acuity?

One-to-one or low convergence onto ganglion cells.

Why can you see stars better in peripheral vision?

Rod convergence gives high sensitivity in the periphery.

What is a receptive field?

The region of the retina that, when stimulated, changes the firing rate of a neuron.

What are the two main types of ganglion cell receptive fields?

ON-centre/OFF-surround and OFF-centre/ON-surround.

How does the centre-surround structure respond to uniform illumination?

It responds weakly because excitation and inhibition cancel out.

Why do ganglion cells respond most strongly to edges?

Because edges create contrast between centre and surround, producing unequal excitation and inhibition.

What phenomenon does lateral inhibition explain?

Mach bands and edge enhancement.

What is lateral inhibition?

Inhibitory signals from neighbouring cells that exaggerate differences at edges.

Why does lateral inhibition produce the Mach band illusion?

Cells near edges receive different amounts of inhibition, making edges appear brighter or darker than they physically are.

What are the two major ganglion cell classes?

Parvocellular (P-cells) and magnocellular (M-cells).

Which ganglion cell type has smaller receptive fields?

Parvocellular (P-cells).

Which ganglion cell type is more sensitive to motion?

Magnocellular (M-cells).

Which pathway is colour-sensitive?

Parvocellular (P-pathway).

Why are M-cells better for detecting motion?

They have faster conduction velocities and larger receptive fields.

What is contrast?

The ratio of the difference in luminance to the overall luminance.

What does the visual system primarily code: absolute luminance or contrast?

Contrast.

Why is coding contrast more useful than coding absolute luminance?

Because absolute luminance constantly changes (lighting variations), but contrast remains stable and informative.

What is spatial frequency?

How often a pattern repeats across space (e.g., stripes per degree of visual angle).

Which spatial frequencies do ganglion cells respond to best?

Middle frequencies.

Why do ganglion cells not respond well to very low spatial frequencies?

Centre and surround both receive similar illumination → cancellation.

Why do ganglion cells not respond well to very high spatial frequencies?

The alternating light/dark stripes fall within both centre and surround → averaging cancels the response.

What illusion is explained using centre–surround receptive fields?

The Hermann Grid.

Why do dark spots appear at intersections in the Hermann Grid?

Receptive fields at intersections get more inhibition from the surround.

Why do the dark spots disappear when you look directly at an intersection?

Foveal receptive fields are smaller, making the extra inhibition at intersections negligible.

What determines visual acuity at the retinal level?

The density of photoreceptors and the size of receptive fields.

Why is acuity highest in the fovea?

Cones are densely packed and receptive fields are small.

Why does acuity decline in the periphery?

Receptive fields are larger and photoreceptor density is lower.

What key function do ganglion cell receptive fields serve?

Detecting contrast and edges.

Which pathway supports high-detail, colour vision?

Parvocellular pathway.

Which pathway supports motion and low-light sensitivity?

Magnocellular pathway.

Where do most LGN neurons project?

To V1 (primary visual cortex).

What is the main function of V1 neurons?

Detect features such as orientation, spatial frequency, and direction.

What is cortical magnification?

More cortical area is devoted to the fovea than the periphery.

Why does the fovea have more cortical representation?

High acuity needs more processing resources.

How is V1 arranged spatially?

Retinotopically — neighbouring points in space map to neighbouring neurons.

What are orientation columns?

Vertical stacks of V1 neurons that prefer the same orientation.

What is an orientation map?

A 2D pattern showing preferred orientation across the cortex.

Why does V1 need orientation maps?

To represent all possible edge orientations in the visual scene.

What characterizes a simple cell receptive field?

Distinct ON and OFF subregions.

What do simple cells respond best to?

Bars or edges of a specific orientation and position.

What characterizes complex cells?

Orientation-tuned but without distinct ON/OFF regions.

Why are complex cells more tolerant to stimulus position?

They pool input from many simple cells.

What do hypercomplex cells respond to?

Edges of a specific length or lines that end within the receptive field.