Perception - Exam 2 Short Answer

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Objects may appear to be yellowish-green or reddish-blue, but never reddish-green or yellowish-blue. Why is this the case?

Red and green are opposites for humans who are trichromats

Neural wiring of cones into later neurons is set up as an opponent process

When long wavelengths (red) dominate short wavelengths (green) neuron fires rapidly, indicating red

When the reverse is true, neuron fires slowly indicating green

When long and short wavelengths are balanced equally, neuron fires at base, resting rate, indicating neither red nor green ( maybe gray, or blue or yellow)

"Reddish green" is like whitish black, longish short, or biggish small

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What are the two main competing explanations for why we see the Ames Room or the Ames Windows the way we do (as rectangular rather than trapezoidal in shape). Describe each explanation and note whether they are incompatible with one another.

Prägnaz/simplicity/minimum principle

We organize our percepts in a way that maximizes their simplicity (like how a soap bubble automatically assumes the simplest possible shape)

A rectangle is simpler than a trapezoid because it requires fewer parameters to define (2 vs 4) so we prefer to see windows/rooms as rectangles

Likelihood

We organize our percepts in the most likely, plausible way

Virtually all rooms/windows we see are rectangle so we have a bias to interpret these shapes as rectangles when we see them

The two principles are not mutually exclusive in that natural forces often act to make shapes regular and simple (symmetrical body/face on animals; spherical moon), so if we can interpret an object as simple, it probably is simple (non-accidental properties)

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When we describe auditory (sound) stimuli, we can show their full, raw waveform - a tracing of how a loud speaker would vibrate to produce the sound - but these tracings can become very complex. Instead, scientists perform Fourier analysis to represent the stimulus more simply. What is Fourier analysis, and how does a sound appear when potted according to its Fourier components?

Fourier Analysis: breaks down a complex waveform into a set of underlying sine waves that, if added back together, reconstitutes the original wave.

The sine wave components differ in frequency, amplitude, and phase

Single flat line - White noise (appears as a very very complex scrambled line in its raw form), line indicates that the frequencies it contains includes all frequencies

Point - a single sine wave appears as a point as only a single frequency is present

Series of sine waves - a square wave appears as a series of sine waves beginning with the fundamental (basic frequency of square wave) at the greatest amplitude, plus the odd harmonics (third, fifth, etc.) at steadily decreasing amplitudes.

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If we walk around with a handheld video camera and shoot a movie, the images fly all about the screen when we watch it, sometimes making us seasick. Why don't we experience the same disturbing motion when we look with our own eyes while walking, given how our heads move about as we walk? Similarly, why does the world look stationary when we move our eyes with our eye muscles but then seem to move a lot when we move our fingertips?

Appears to be special circuitry in the eye and brain that cancels out any motion that is caused by movements of the eyes or any other body parts.

When we move our eyes with our eye muscles we see the world as stable

The corollary discharge system creates an efferent copy of the signal telling the eye muscles to move the eye and then sends it over to the brain regions that let us see motion, effectively canceling movement caused by our movement of the eye

When we move our eyes with our fingers we see the world move

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What is "crossed binocular disparity"? Start by saying what binocular disparity is, and then say what it means for it to be crossed.

Binocular Disparity

When we focus on an object with our eyes, the image of that object falls on corresponding parts of the retina in each eye

Other objects in our field of view that are closer or farther to our eye than where we are fixating fall on different sections of the two retinas

Those nearer and further objects fall on different, or disparate, parts of the two eyes

Crossed Binocular Disparity

Occurs when the object is closer than where we are focused

The image of the object is shifted toward the left in the right eye and toward the right in the left eye, relative to the object being fixated

The degree of crossed disparity tells the brain how much closer the near object is than the object being fixated

All objects at the same distance from the eye as the object being fixated have no disparity; they fall on a curved, roughly spherical imaginary surface called the horopter.

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What is multistability in perception? Give a couple of examples.

Multistability: perceiving a given stimulus in two or more different ways, generally with rapid switching among the interpretations, an alternation that is not fully under our conscious control. With multistability we actually perceive the "flipping" of the interpretations

Examples:

Necker Cube

Barber pole

Rubin faces/vases

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The chapter in the Yantis book by Hurvich and Jameson on the opponent process theory of color vision describes a hue-cancellation method used to discover how theses color processes work. What is this method?

Observers are shown a single wavelength that, alone, is perceived as yellow

They are given control over how much of another wavelength (that is alone perceived as blue) they add to the yellow

Considering blue and yellow are opposites, adding blue to the yellow will diminish the yellow

Observers are asked to keep adding blue just until the yellow is entirely gone

When the null mixture is obtain the light looks neither blue nor yellow but may appear green or red

The procedure is then repeated with another wavelength, and so on until the spectral distribution curve is swept out

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Many people fail to notice the hidden arrow in the FedEx logo. What principles reviewed in this class help explain why the arrow can be so hard to spot?

This is an example of figure ground segregation rules making it hard to see the arrow as figure and not as a shapeless background between the letters. Some figure ground rules might favor seeing the arrow as ground:

The arrow is small when compared to the "E" on the left

It contains concave regions

It is surrounded by contours from the letters

It is the same color as the surround for all five letters

The high familiarity if the letters also makes them more likely to be figure, especially with 5 of them in a row