PSC 129 - Sensory Processes

Midterm 2 - review sheet

Visual cortex

What do the what and where processing streams refer to, and what cortical areas are the major players in these streams?

What is the contrast sensitivity function?

How may adaptation experiments be used to study neural mechanisms of perception? What are the effects of adaptation on sensitivity and discrimination?

What does topographic organization refer to?

Color vision

What is the physical basis of color? i.e., what physical property of light does color refer to?

What does the term trichromacy refer to? What are the implications of trichromacy for human color perception?

What are the three cone types - i.e., what are their approximate wavelength selectivities?

How are the different cone types distributed across the retina? What is the relative prevalence among the population of cones for each type?

What does the term color opponency refer to? What is the meaning of chromatic and achromatic channels? How do these channels pool information from the different cone types?

Consider the difference between tones of different frequencies and colors of different wavelengths. When you mix two tones, you hear a chord which sounds unlike any one note played alone. But when you mix light of two colors (e.g., green and red) you perceive only one color (yellow), not a combination of the two as in a musical chord. Why?

Why is it that mixing red and green ink does not give rise to the same percept as mixing red and green light?

What is a metamer? What is an example of a color metamer, and why does this happen?

What does color constancy refer to? What are its advantages? What are its disadvantages?

What is lightness constancy?

Depth perception

What are the various cues - both non-visual and visual - that the visual system can use to ascertain the relative depths of objects in a scene?

What is stereopsis? What is disparity?

Draw a diagram illustrating the viewing geometry that gives rise to disparity. Show the horopter and the disparities that would result from objects in front or in back of the horopter .

What is a random-dot stereogram? How is it created, and what does the perception of depth in these images imply about the mechanisms used for computing depth in the visual system?

What is binocular rivalry?

What is occlusion and how does it contribute to depth perception?

What is size constancy? Why does size constancy break down in the Ames room, or in the moon illusion.

What is motion parallax, and how does it contribute to depth perception?

What is meant by a texture gradient, and how does it provide a cue to depth?


What does the critical flicker frequency or flicker fusion frequency refer to? What is this frequency for human vision?

Draw a diagram of a simple neural circuit for detecting motion to the right, and explain how it works.

How is the computation of motion similar to the computation of depth via stereopsis?

What does the aperture problem refer to? Why does it give rise to illusions such as the Barber pole illusion?

What is optic flow? Why is it important?

What is the waterfall illusion? Why does it occur?

What does efference copy mean, and how is it used to maintain perceptual stability in the face of eye movements?


What creates sound? What is a sound wave?

What does the frequency of sound refer to? What is the frequency range of human hearing? How does this compare to other animals such as bats and dogs?

What does it mean to say that two sounds differ by 20 dB in intensity? What does it mean to say they differ by 40 dB? Why do we use the decibel scale to measure sound intensity?

Identify the major parts of the ear on a diagram - outer, middle, and inner ear - along with a one sentence description of their function.

How are vibrations transformed from the eardrum to the cochlea via the middle ear, and what problem of sound transduction is being mitigated here?

What is the basilar membrane? What is its functional significance?

Identify on a diagram the portions of the basilar membrane that resonate in response to low-, medium-, and high-frequency vibrations. What would be the approximate resonant frequencies in these different regimes? What is the relation between resonant frequency and width/stiffness?

What is meant by a log-frequency representation? What are the perceptual consequences of a log-frequency representation?

What are hair cells and what do they do?

Inner and outer hair cells: how many of each are there (approximately), and what are their relative contributions to the auditory nerve fibers?

How many nerve fibers - or axons - constitute the auditory nerve?

What does the frequency tuning curve of an auditory nerve fiber refer to?

What physical factors within the ear give rise to the frequency tuning curve of an auditory nerve fiber? What is the approximate typical bandwidth, in terms of octaves, of an auditory nerve fiber?

What are interaural intensity differences (IID) and interaural time differences (ITD), and how does the brain use these cues to localize sound?

What is the auditory cortex? What does it mean to say that the neural representation in the auditory cortex is tonotopic?

What is pitch and how is it different from frequency?

What are harmonics? What is their mathematical relation to the fundamental?

What is timbre? What are the physical attributes of a tone that determine its timbre?

What does the missing fundamental refer to? i.e., if you heard a complex tone consisting of pure tones at 200, 300, 400, 500, & 600 Hz, what would be the fundamental frequency of the perceived pitch?

What are the various perceptual grouping rules that the brain uses to segment a voice from the crowd?

What does cortical plasticity refer to? Under what circumstances has plasticity been observed in the adult primate brain?

How does the representation in auditory cortex become altered by practice?

In what sense does the term loudness differ from intensity?

What is a spectrogram, how is it used to analyze sound?

What is a phoneme?