Psych 129 - Sensory Processes

Mid-term 1 - review sheet


What is light? What is an electromagnetic wave?

What region of the electromagnetic spectrum does visible light occupy with respect to X-rays, ultraviolet, infrared, and radio/TV? (both in terms of frequency and wavelength)

How do you form an image? - i.e., how do you make a photoreceptor directionally selective so that different photoreceptors respond to different parts of visual space?

The eye

Identify on a diagram the major parts of the human eye - cornea, lens, iris, and retina - along with a brief statement of their function.

What is the fovea? What is the optic disk? What causes the blind spot?

What are floaters and in what part of the eye do they reside?

What does depth of field refer to, and how does it relate to the iris?

The retina

On a diagram showing the fine structure of the retina, identify the photoreceptors and ganglion cells, along with a brief statement of their function, and show which way light is coming from.

Rods and cones: What are they? What are their overall number and spatial distribution as a function of location in the retina? What are their differences in terms of overall sensitivity and also the wavelength of light they are most sensitive to? What is their relation to photopic and scotopic vision, and what are the perceptual consequences of working in these two regimes?

How many photoreceptors per eye? How many ganglion cells? What is the relation to resolution?

How are the ganglion cells spatially distributed across the retina? What are the perceptual consequences of this sampling strategy? Why does this scheme make sense?

What is aliasing, and does it become an important issue in the design of the eye?

What is a receptive field?

What do ganglion cell receptive fields look like? - i.e., draw a picture of how the excitatory and inhibitory subregions are spatially arranged for a so-called "ON" cell. Do the same for an
"OFF" cell.

How do the sizes of ganglion cell receptive fields change as a function of eccentricity?

Why are eccentricity and object size usually measured in degrees?

How do you calculate (approximately) the number of degrees subtended by an object in the visual field?

On a diagram, show how a ganglion cell with a given receptive field type (i.e., ON or OFF) and size will respond when a luminance edge is placed at various locations with respect to its receptive field.

Visual pathways

On a diagram of the brain, identify the major structures in the information pathway of the visual system: retina, optic nerve, optic chiasm, optic tract, superior colliculus, LGN, and visual cortex.

What is blind sight?

What makes the flow of information between LGN and cortex different from the flow of information between retina and LGN? Why should the word "relay nucleus" be used with caution when describing the LGN?

Visual cortex

What does topographic organization refer to? In what way is the topographic map in V1 distorted relative to the retina?

Explain the properties of orientation selectivity and spatial-frequency selectivity of visual cortical neurons with reference to a diagram of their receptive fields.

What do the terms binocularity and ocular dominance refer to?

Explain the orderly, columnar arrangement of orientation selectivity and ocular dominance in V1 with reference to a diagram.

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?

What is distributed coding? How may adaptation experiments be used to study distributed codes in the brain?

What are the effects of adaptation on sensitivity vs discrimination?

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?

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?