PSY252 Textbook questions

A laser pointer emits light of a single wavelength, whereas an ordinary lamp emits light spread across many wavelengths with no dominant one. Which pair of terms describes the two lights, in that order?

Monochromatic; heterochromatic (white)

A lighting designer graphs the intensity of a bulb's light at every visible wavelength, and a paint chemist graphs the percentage of light a surface reflects at every wavelength. Which pair of terms names these two graphs, in that order?

Spectral power distribution; spectral reflectance

The reflectance curves for black, gray, and white paper are all roughly flat lines, but at different heights on the graph. What does the height of each curve indicate?

The overall percentage of light the paper reflects (high for white, low for black)

White light is added to a saturated monochromatic red light. According to the chapter, what happens to the perceived color?

Its saturation decreases, although its hue has not changed

Why are the 'nonspectral purples' on the color circle called nonspectral?

No single wavelength produces them; they can only be created by mixing long-wavelength (red) and short-wavelength (violet) light

In a color solid, which dimension varies vertically, and what happens to the radius (the range of saturation) near the top and bottom?

Brightness varies vertically; the radius shrinks, matching the perception that very bright or very dim colors look less vivid

At 550 nm, blue paint reflects about 28% of incident white light and yellow paint about 55%. Roughly what percentage does a mixture of the two reflect at 550 nm, and why?

About 15%, because the reflectances of the substances are multiplied (each pigment keeps absorbing the wavelengths it absorbed before)

Red and green spotlights partly overlap on a white screen. What is perceived where they overlap, and why is this an additive mixture?

Yellow; the reflected light contains the sum of the wavelengths from both lights

Two fully saturated lights that lie opposite each other on the color circle (such as red and cyan) are mixed in equal intensities. What is perceived?

A shade of gray, because the mixture falls at the center of the color circle

Why are red, green, and blue a better set of additive primaries than three hues that lie close together on the color circle?

They are spaced evenly around the circle, so the triangle connecting them is as large as possible and encloses the widest range of mixture colors

A dim 543 nm light and a bright 450 nm light can produce identical responses from a single M-cone if their intensities are chosen appropriately. Which principle explains this?

Principle of univariance: once a photon is absorbed, the response is the same regardless of the photon's wavelength

Why does night vision, which depends only on rods, lack color?

With a single receptor type, lights of different wavelengths can produce identical responses and differ only in perceived intensity (univariance)

A person has only M-cones and L-cones. In a metameric color-matching experiment, how many monochromatic comparison lights does the person generally need to match any test light, and what does this number indicate?

Two; the number of lights needed equals the number of cone types

Which technique has produced direct images of the mosaic of S-, M-, and L-cones in the living human retina, showing that S-cones are only a small proportion (roughly 5%) of cones?

Retinal densitometry

When people sort color cards into piles of similar colors, most make four piles that they would call red, green, blue, and yellow. Why is this difficult for a strictly trichromatic account?

Trichromacy implies three basic colors, not four, and cannot explain why colors seem to come in opposing pairs; Hering interpreted the four piles as two opponent pairs

Orange looks like a mixture of red and yellow, and purple like a mixture of red and blue, yet people never describe a color as 'reddish green' or 'bluish yellow.' What did Hering conclude from observations like this?

Red-green and blue-yellow are opponent pairs, so the two members of a pair cannot be perceived together in one color

In a hue-cancellation experiment, an observer views a 550 nm light that looks yellowish green and adds blue light until no yellowness remains. What does the amount of blue light needed estimate?

The perceived amount of yellowness in the original light

A monochromatic light is perceived as 'unique green.' What does this mean?

It is perceived as having neither blueness nor yellowness (a pure green, not a combination)

In the 1950s, which finding provided the first physiological evidence for opponent color representation?

Single cones in the fish retina that responded in opposite ways to wavelengths from different parts of the spectrum

A retinal ganglion cell receives excitatory input from L-cones and inhibitory input from M-cones in its receptive field. Which circuit is this, and how does the cell respond?

A +L-M circuit; it fires above baseline to long-wavelength light and below baseline to medium-wavelength light

Which pair of retinal ganglion cell circuits is thought to support the perception of blue and yellow as basic, opposite colors?

+S-ML and +ML-S circuits

A V1 neuron increases its firing rate when its receptive-field center is stimulated by long-wavelength (reddish) light and its surround by medium-wavelength (greenish) light, and is suppressed by the reverse arrangement. What information does this double-opponent neuron provide?

The location of edges between regions that differ in color

Which statement correctly describes the cone mosaic revealed by retinal densitometry?

S-cones are a small minority (roughly 5%), and the ratio of M- to L-cones can differ greatly between people with normal color vision

The idea that normal color vision depends on three types of retinal receptors, proposed in 1802 and later popularized by Helmholtz, is credited to which scientist?

Thomas Young

Newton wrote that 'the Rays to speak properly are not coloured.' According to the chapter, what does this imply about color?

Color is a perceptual experience evoked by the wavelengths of light reaching the eye, not a property of the light or objects themselves

Which photoreceptor's photopigment is most sensitive to light of about 500 nm, and is far more sensitive in absolute terms (about 100 times) than the M-cone photopigment at its peak?

Rods

A red balloon is deflated to half its size and moved along the line of sight to half its original distance from a one-eyed viewer, and the retinal image does not change. What general problem of depth perception does this illustrate?

The 2-D retinal image is consistent with many different 3-D scenes (a many-to-one relationship)

Oculomotor depth cues arise from the workings of which two sets of muscles?

Muscles that control the shape of the lens and muscles that control the position of the eyes

A friend walks toward you across a field and you keep her face in focus. How do your ciliary muscles and lens change as she approaches?

The ciliary muscles contract and the lens becomes more rounded

Why do accommodation and convergence help you judge the distance of a friend 1 m away but not of a friend 100 m away?

Beyond roughly 2 m the angle between the lines of gaze barely changes (and accommodation is similarly uninformative), so the muscle feedback carries little depth information

A red rectangle abuts a blue shape so that their edges form T-junctions. Why do we usually see the red rectangle occluding a complete blue rectangle rather than fitting into a notch in the blue shape?

The notch interpretation would require a highly unlikely accidental alignment of the shapes with the viewer's line of sight, so we assume the simpler continuation behind the occluder

A classroom has desks resting on the floor and light fixtures attached to the ceiling. Which statement about relative height is correct?

For desks, objects whose bases are lower in the retinal image are closer; for ceiling fixtures, those attached higher in the image are closer

A tree is moved to twice its original distance from the eye. According to the size-distance relation, what happens to the size of its retinal image?

It decreases by half, in proportion to the increase in distance

An astronaut sees a colleague floating against a black background with nothing else visible. The colleague's retinal image is about half the size of the image of a person of that height standing 4 m away. Which cue lets the astronaut estimate that the colleague is about 8 m away?

Familiar size

In a photo of two cyclists, the rear cyclist's retinal image is half as tall as the lead cyclist's. Even if the cyclists were aliens of unknown size, what could you conclude if you assumed they were about the same size?

The rear cyclist is about twice as far away (relative size)

The stones on a dry riverbed produce retinal images that get smaller and more closely spaced with distance, creating a strong impression of depth. This texture gradient is a special case of which cue?

Relative size

Why do distant mountains often look bluish as well as less distinct?

Atmospheric haze scatters short-wavelength (blue) light more than other wavelengths, and more air lies between the viewer and distant objects

In a pattern of shaded discs the center disc looks raised and the surrounding discs look indented; when the pattern is turned upside down the percepts reverse. Which unconscious assumption explains this?

A single light source is illuminating the scene from above

In a photo, a running woman is higher in the image than a standing man, which by relative height suggests she is farther away. Her cast shadow, however, shows that she is at the same distance but above the ground. What does this show?

Cast shadows can reveal an object's position in depth and show when relative height is misleading

You walk from left to right while fixating a red rock in the desert. A cactus nearer than the rock and another farther than the rock are in view. In which directions do they appear to move relative to your own direction of motion?

The nearer cactus appears to move opposite to your direction of motion; the farther cactus appears to move in the same direction

Driving down a straight road toward a mesa while looking at it, you see the whole landscape flow outward in your retinal image except for one point. What is that point, and why is it significant?

The focus of expansion, the point you are heading toward; other elements move away from it at rates that depend on their distance

A man walking across the street gradually disappears behind the left edge of a newsstand and later gradually reappears from behind its right edge. Which terms describe these two events, and what do they indicate?

Deletion, then accretion; the man is farther away than the newsstand

Which pair of retinal points are corresponding points?

The foveas of the left and right eyes

An observer fixates a red object. A brown object lies closer to her than the horopter. What type of disparity do its retinal images show, and what would she have to do with her eyes to fixate it?

Crossed disparity; she would have to increase convergence (cross her eyes more)

Which retinal images exhibit zero binocular disparity?

Images of the fixated object and of other objects on the horopter, which fall on corresponding points

As an object's distance from the horopter increases, what happens to the magnitude of its binocular disparity?

It increases, whether the object is nearer than or farther than the horopter

Stereopsis typically provides useful information about relative depth out to roughly what distance?

About 200 m

What is the correspondence problem in stereopsis?

Determining which features in one eye's retinal image correspond to which features in the other eye's image

One hypothesis about the correspondence problem proposes that the visual system matches parts of the two retinal images using simple properties before object recognition occurs. Which properties does the chapter give as examples?

Color or edge orientation

A photographic stereogram is made by mounting two cameras side by side. Why are the lenses separated by about 6 cm?

To approximate the average distance between adult human eyes, so the two photos differ as the two retinal images would

A woman with strabismus suppresses the vision of one eye at a time and is stereoblind. Which depth cues could she still use?

Monocular cues such as partial occlusion and motion parallax

Movies shown at 24 frames per second create the experience of motion even though they are sequences of still images. Which phenomenon underlies this?

Apparent motion

A circle flashes at one location and, within about 150 ms, a square flashes at another location. What do observers typically perceive?

A single object moving between the locations and changing shape

A display contains several apparent motion quartets. When the perceived direction of motion flips from horizontal to vertical in one quartet, all the others flip at the same time. Which principle does this illustrate?

Common motion

In an apparent motion quartet, the dots are closer together vertically than horizontally. Which perceived motion is favored?

Vertical motion

In a random dot kinematogram, a rectangular region of dots moves rigidly and the rectangle is visible only while the dots move. What does this demonstrate?

Motion discontinuities alone, without differences in brightness, color, depth, or texture, can define a shape against its background

What most crucially determines whether a point-light display is recognized as a walking person?

The coordinated timing of the motions of the points

As a person walks, the distance between the elbow and the wrist stays constant while the distance between the wrist and the ankle changes a great deal. What term describes the body's motion?

Piecewise rigid

fMRI shows increased activity in a temporal-lobe region when people view a point-light walker (compared with randomly moving dots), and TMS over that region impairs the perception of biological motion. Which region is it?

Posterior superior temporal sulcus (STSp)

Participants watch spots moving around a display. They are faster to detect the disappearance of a spot that has just changed direction without any apparent cause, and faster still when the change was larger. What does this suggest?

Animate motion captures attention, more so when the direction change is larger

In a simple motion-detecting circuit, Neuron M fires strongly only if signals from Neuron 1 and Neuron 2 arrive simultaneously. Why is a delay in the signal from one of those neurons necessary?

So that signals triggered by a feature moving in the preferred direction at the preferred speed arrive at Neuron M at the same time

In the simple motion circuit, what determines whether the neuron prefers rightward or leftward motion, and what determines its preferred speed?

Direction depends on which neuron's signal is delayed; speed depends on the length of the delay

Why can a motion-selective neuron respond to apparent motion almost as it does to real motion?

A flash at one receptive field followed after a suitable delay by a flash at the other produces the same coincident arrival of signals as a moving spot

Where in the primate visual pathway are neurons tuned for direction and speed of motion first found?

Area V1

After staring at a waterfall for a few minutes, a stationary rock wall appears to drift upward. In the opponent-circuit explanation, why does this occur?

The neuron that responded to the downward motion becomes fatigued and fires below baseline, so the comparison of opposite directions signals upward motion

Why is motion represented as the difference between the responses of two oppositely tuned neurons rather than by monitoring a single neuron?

A single neuron's response depends on many factors (speed, contrast, orientation, disparity), so its firing alone is ambiguous about direction

Compared with V1 neurons, MT neurons have receptive fields that are:

About 5-10 times larger in diameter, which suits them to large-scale motions

Unlike neurons at higher levels such as V4 and the inferotemporal cortex, MT neurons are tuned to which stimulus property?

Direction of motion, but not color, curvature, or shape

fMRI compares human brain activity in V1 and MT while observers view a blank screen, moving dots, or stationary dots. Which pattern is found?

V1 responds about as much to stationary dots as to moving dots, whereas MT responds strongly only to moving dots

Monkeys trained to report the direction of dot motion received a tiny electrical current to an MT neuron tuned to rightward motion. What did the monkeys tend to do?

Respond as if the dots had moved rightward, evidence that MT activity causes the perception of motion

In a motion-coherence display, what does 33% coherence mean?

One-third of the dots move in the same direction while the rest move randomly

At 0.8% coherence a monkey's direction judgments were just above 50% correct. How did the recorded MT neuron respond?

About the same for motion in its preferred direction and in the opposite direction, so spike counts could not distinguish them

Across coherence levels, how did the performance of individual MT neurons compare with the monkey's judgments?

It was not significantly different, suggesting the judgments could be based on the responses of a population of MT neurons

A woman with bilateral damage that includes area MT can no longer perceive visual motion but can perceive motion through hearing and touch. What does this suggest?

Area MT is critical for visual motion perception in particular

A V1 neuron with a small receptive field sees only a vertical edge moving to the right, whether the object is moving directly right or up and to the right. What is this limitation called?

The aperture problem

How is the aperture problem thought to be solved?

MT neurons with large receptive fields combine the signals of several V1 neurons that prefer different directions

Two sets of stripes, one moving directly right and one moving directly up, are superimposed. They have similar thickness and speed. What do people typically perceive?

A single plaid pattern moving diagonally up and to the right

What distinguishes visually induced motion sickness (VIMS) from the motion sickness that occurs while traveling by car or boat?

VIMS is associated with the perception of motion in artificial environments such as movies, video games, or VR displays

As a tuning fork vibrates, what happens to the air next to it, and what actually travels outward?

Regions of compression and rarefaction alternate, and the pressure wave travels outward while individual air molecules only oscillate over short distances

Why does an ambulance siren sound much quieter when it is far away than when it is near, even though the source emits the same amount of sound?

The expanding wave front spreads the sound energy over a larger area, so the energy at any point falls with the square of the distance

Which pairing correctly matches each physical dimension of sound with the perceptual dimension it is most closely related to?

Frequency-pitch; amplitude-loudness; waveform-timbre

A bat's echolocation click has a frequency of 60,000 Hz. Could a young adult with normal hearing detect it if it were made loud enough?

No; human hearing is limited to roughly 20-20,000 Hz, no matter how loud the sound

A sound has a sound pressure of 20,000 micropascals. Using the reference pressure of 20 micropascals, what is its amplitude in dB SPL?

60 dB SPL

A sound has a pressure of 10 micropascals, half the 20 micropascal reference. What is its sound pressure level?

About -6 dB SPL, a negative value because the pressure is below the reference

Besides keeping the numbers small, why is amplitude expressed in decibels?

Perceived loudness increases by roughly a constant amount each time sound pressure doubles, and the just noticeable difference is about 1 dB at any level, so decibels track perception better than micropascals

Young adults with normal hearing can detect a 1,000 Hz tone at about 0-5 dB SPL, but need about 40 dB SPL to detect a 100 Hz tone. What does this show?

They are much more sensitive to 1,000 Hz tones than to 100 Hz tones; the audibility curve is not flat

One listener has an absolute threshold of -3 dB SPL for a 1,000 Hz tone and another has 0 dB SPL. Who is more sensitive to 1,000 Hz tones?

The first listener, because a less intense tone is enough to be detected

The auditory canal does more than funnel sound onto the tympanic membrane. Which frequencies does it amplify, contributing to our high sensitivity at those frequencies?

About 2,000-5,000 Hz

A 1,000 Hz tone at 50 dB SPL has a loudness of 50 phons. What does it mean that a 125 Hz tone of about 68 dB SPL lies on the 50-phon equal loudness contour?

It sounds just as loud as the 1,000 Hz tone at 50 dB SPL

The equal loudness contours become flatter as amplitude increases. What does this indicate?

Differences in sensitivity across frequencies shrink at higher amplitudes; the mid-range advantage matters mainly for quiet sounds

A complex periodic sound is made up of pure tones of 100, 200, and 300 Hz. What pitch will it have, and why?

That of a 100 Hz pure tone, because the fundamental (the lowest-frequency component) determines pitch

A clarinet plays A880, which has a fundamental frequency of 880 Hz. What is the frequency of its third harmonic?

2,640 Hz

A flute and a violin play G4 at the same loudness, and their harmonics occur at the same frequencies, yet they sound different. What accounts for the difference in timbre?

The relative amplitudes of the harmonics differ (the flute is dominated by the first few harmonics; the violin has energy at many higher harmonics)

A recording contains tones of 160, 240, and 320 Hz and is played through a speaker that cannot emit frequencies below 100 Hz. What pitch do listeners perceive?

About 80 Hz, the missing fundamental

If the initial and final segments of a piano note and a violin note are trimmed away, leaving only the sustained parts, what happens?

It becomes much harder to tell which instrument produced which note, because attack and decay contribute to timbre

Besides funneling sound toward the auditory canal, what contribution does the shape of the pinna make?

It modifies the incoming sound in a way that contributes to sound localization

Through which sequence are vibrations transmitted from the tympanic membrane to the cochlea?

Malleus, incus, stapes, oval window

If sound waves in air were transmitted directly to the fluid-filled cochlea, with no middle ear mechanism, what would happen?

There would be about a 30 dB loss in sound energy, because most of the energy would be reflected rather than transmitted

Which two features of ear anatomy together amplify sound by roughly 20-30 dB, offsetting the loss in transmission from air to cochlear fluid?

The tympanic membrane is 15-20 times larger than the oval window, and the ossicles act as a lever

Your ears feel muffled in a fast elevator, and swallowing restores normal hearing. Why?

Swallowing briefly opens the Eustachian tube, equalizing the middle-ear air pressure with the outside air