Ch. 8 The Psychology of Vision

What abilities are preserved in people with damage to the "what" pathway but lost in people with damage to the "where and how" pathway?

Ability to reach accurately for objects and act on them in coordinated ways, using vision to guide actions.

How does additive color mixing differ from subtractive color mixing? What are the two laws of additive color mixing, and how is each illustrated in the standard chromaticity diagram?

Additive color mixing is the mixing of lights, not pigments. Three-primaries law: three wavelengths of light can be be used to match any color that the eyes can see if mixed in appropriate proportions. Law of complementarity: pairs of wavelengths can be found that, when added together, produce visual sensation of white.

What problem was Biderman's recognition-by-components theory designed to explain? What is the theory, and how is it supported by experiments on object recognition by people with intact brains?

Attempt to explain how we see an object as the same object independent of orientation. Theory: visual system first organizes stimulus info into basic 3-D components called geons, then uses arrangement of components to recognize object. Speed and ability to recognize object depends very much on intactness and arrangement of geons and very little on other aspects of stimulus such as detail.

How do stereoscopes provide an illusion of depth?

Combines images, one as seen by left eye, one as seen by right eye.

How does the opponent-process theory explain (a.) the law of complementarity in color mixing and (b.) the complementarity of afterimages?

Complements have opponent neurons, which are stimulated by one of the wavelengths and inhibited by the other, and vice versa. Other brightness neurons distinguish between bright and dim based on stimulation by any wavelength. Thus a mixture of complementary colors cancels each other out but stimulates brightness receptors. Afterimages: neurons that perceive a certain color become fatigued after staring at color, when eye shifts to white paper they don't respond as they normally would, but the opponent neuron does. In case of green, green becomes fatigued so when eye shifts to white paper, only red appears.

How do cone vision and rod vision differ?

Cone vision (photopic vision): specialized for high acuity and color perception Rod vision (scoptic vision): specialized for sensitivity

How are cones and rods distributed on the retina, and how do they respond to light?

Cones: sharply focused color vision in bright light; most concentrated in fovea in direct line of sight, which is specialized for high visual acuity (ability to distinguish tiny details); three different photochemicals for each of the three types of cone Rods: vision in dim light; exist everywhere in retina except fovea, especially abundant in ring 20 degrees from fovea; rhodopsin is photochemical Photochemicals respond to light and result in conformational change of membrane proteins, leading to receptor potential carried by optic nerve to brain

How do the cornea, iris, and lens help to form images on the retina?

Cornea's convex curvature helps focus light that passes through it. Iris is opaque, so only light that can enter interior of eye is that which passes through pupil. Adjustable lens focuses bring light rays back to a certain point on the retina, which forms an image of the object on the retina.

What is the difference between parallel processing and serial processing? What role does each play in Treisman's feature-integration theory of perception?

Detection of features occurs simultaneously: parallel processing-- step operates simultaneously on all parts of the stimulus array integration of features occurs sequentially: serial processing -- can integrate features of one spatial location at a time

What is the value of the visual system's ability to exaggerate contrast at contours, and how can that ability be demonstrated? How is contrast enhancement explained by lateral inhibition?

Exaggeration of contrast at contours helps us to see objects as distinct from their neighbors. Can be demonstrated by adjacent bars (fig 8.15 p 282). Activity in any given neuron declines when its neighboring neurons are active, by an amount that is proportional to the degree of activity in those neighbors.

How can light be described physically, and what is the relationship of its wavelength to its perceived color?

Light is described in waves or packets of energy called photons. Shortest-->longest: violet, indigo, blue, green, yellow, orange, red.

Through what steps might sophisticated eyes like ours have evolved from primitive beginnings?

Light sensation; shadow sensation to avoid predators; sink into pits to reduce glare; transparent lens to magnify light; lens can project image onto photoreceptors; etc.

What are the anatomical and functional distinctions between two different visual pathways in the cerebral cortex?

Lower, temporal stream: "what" pathway; specialized for identifying objects Upper, parietal stream: "where and how" pathway; specialized for maintaining map of 3-D space and localizing objects within space; also crucial for use of visual info to guide a person's movements

How does the pattern of neural connections within the retina help account for the greater sensitivity and reduced acuity of rod vision compared with cone vision?

Many rods converge onto few bipolar cells, which converge onto fewer ganglion cells leading to optic nerve; thus stimulation of many rods is funneled and creates greater potentials in optic nerve. This means that when rods that are part of the same converging system are both stimulated, however, the fact that it funnels into one ganglion cell means the mind can't differentiate the location or which ones are stimulated. Cones have little or no convergence.

What are some cues for depth that exist in pictures as well as in the actual, three-dimensional world?

Occlusion: objects closer cut off objects farther away Relative image size for familiar objects: e.g. we know woman isn't taller than mountains, so if she appears taller it's because she's closer to us Linear perspective: convergence of lines as they travel toward horizon Texture gradient: texture elements smaller and more densely packed closer to horizon = father away Position relative to horizon: objects nearer horizon = father away Differential lighting of surfaces: how light is cast on objects and shadows are cast by objects

How do illusory contours illustrate the idea that the whole influences the perception of parts? How are illusory contours explained in terms of unconscious inference?

Perceptual system uses initial stimulus input o infer what must be present (based on what makes most sense), and then it creates that by influencing feature-detection processes in the brain in such a way as to produce the feature where one does not physically exist in the stimulus (think of triangle overlaying the circles).

How do pigments affect the perceived color of an object in white light? How does the mixing of pigments affect color by subtracting from the light that is reflected to the eye?

Pigments are chemicals that absorb certain wavelengths of light and thus prevent that wavelength from being reflected in white light. Mixing pigments subtracts the respective wavelengths from the light that will be reflected (e.g. yellow and blue mixed makes green because neither yellow nor blue can be reflected).

How do pop-out phenomena and mistakes in joining features provide evidence for Treisman's theory?

Pop-out phenomena occur (easy to find single different object) because parallel processing of certain features is simultaneous. Mistakes in joining features (flash of red line and green curve, can identify that something was red and something green, but not which was which) indicate that parallel processing is independent of spatial location, but serial (integration) requires separate attention to each spatial location.

What are some principles of grouping proposed by Gestalt psychologists, and how does each help explain our ability to see whole objects?

Proximity - stimulus elements that are near each other are seen as parts of the same object Similarity - stimulus elements that physically resemble each other are seen as parts of the same object Closure - we tend to see forms as completely enclosed by a border and to ignore gaps in the border Good continuation - when lines intersect, we tend to group the line segments in such a way as to form continuos lines with minimal change in direction Common movement - when stimulus elements move in the same direction and at the same rate, we tend to see them as part of a single object Good form - perceptual system strives to produce percepts that are elegant - simply uncluttered, symmetrical, regular, and predictable

How did Helmholtz describe perception as a problem-solving process?

Seeing is active mental process - light focused onto retina is only source of hints about scene, brain infers characteristics and positions of objects form cues in reflected light, and those inferences are perceptions

How has the opponent-process theory been validated in studies of the activity of neurons that receive input from cones?

Some ganglion cells behave in opponent manner in which they are excited by input from a certain cone type and inhibited by input from opponent type (e.g. red excitatory, green inhibitory) (fig. 8.14 pg. 281)

Why does vision in some people obey a two-primaries law rather than a three-primaries law, and why are these people not good at picking cherries? How does the color vision of most non-primate mammals, and that of most birds, differ from that of most humans?

Some people only have two types of cone photochemicals; they are colorblind, if red-green colorblind, can't differentiate cherries from leaves. Most nonprimate mammals have two types (green and blue); most birds have four types (red, blue, green, ultraviolet).

What sorts of stimulus features influence the activity of neurons in the primary visual cortex?

Specific neurons (feature detectors) best stimulated by specific features: edges, angle of tilt, color, movement, etc.

How do reversible figures illustrate the visual system's strong tendency to separate figure and ground, even in the absence of sufficient cues for deciding which is which?

The same part of the figure can not be simultaneously both figure and ground, and thus at any instant you may see either one form or the other, but not both.

How does the trichromatic theory explain the three-primaries law? How was the theory validated by the discovery of three cone types?

Trichromatic theory: color vision emerges from combined activity of three receptors, each most sensitive to a different range of wavelengths. One can match any color by varying relative intensities of three primary lights. Three cone type discovery confirmed theory as we only have three cone types but can see any color: thus color is a combination of the three cone types (blue, green, red).

How is unconscious inference described as top-down control within the grain? What is the difference between top-down and bottom-up control?

Unconscious inference: neural activity from higher brain areas are able to bring together the pieces of sensory info and make complex calculations concerning them Top-down: control that comes from higher brain areas Bottom-up: control that comes from sensory input

How is the recognition-by-components theory supported by the existence of two types of visual deficits cause by brain damage?

Visual form agnosia: see that something is present and identify some elements, but cannot perceive its shape. People can detect elements but not integrate them into geons. Visual object agnosia: describe and draw shapes but cannot identify the objects. Can see 3-D components but can't integrate them to identify object

In sum, what are the distinct functions of the "what" and "where and how" pathways?

What - conscious vision Where and how - rapid, unconscious, automatic visual control of movements with respect to objects

size constancy

ability to see object as unchanged in size despite change in image size as it moves farther away or closer

How does binocular disparity serve as a cue for depth?

binocular disparity - slightly different views that two eyes have of the same object or scene; degree of disparity between two eyes' views serve as cue to object's distance from eyes -- less disparity, greater distance

What is the chemical basis for dark adaptation and light adaptation? Why do we see mostly with cones in bright light and with rods in dim light?

dark adaptation: gradual increase in sensitivity when you enter a darkened room or turn off lights; rhodopsin hasn't regenerated from being in bright light and cones don't work light adaptation: decrease in sensitivity when you turn on a bright light or step into sunlight; rods are still firing before enough time passes for rhodopsin to be broken down Rhodopsin breaks down in bright light, making rods nonfunctional.

retina

membrane lining the rear interior of the eyeball

How does motion parallax serve as a cue for depth, and how is it similar to binocular disparity?

motion parallax - changed view one has of a scene or object when one's head moves sideways; degree of change in either eye's view at one moment compared with the next as head moves in space can serve as cue for assessing distance from eyes: smaller change = greater distance from eye; motion parallax, change in vantage point from movement of head, binocular parallax (disparity) change in vantage point from separation of two eyes

Why does size perception depend on distance perception?

size of retinal image of object is inversely proportional to objects distance from retina

photoreceptors

specialized light-detecting cells