Ch 5 Questions

What theories help us understand color vision?

According to the Young-Helmholtz trichromatic (three-color) theory, the retina contains three types of color receptors. Contemporary research has found three types of cones, each most sensitive to the wavelengths of one of the three primary colors of light (red, green, or blue). According to the opponent-process theory, there are three additional color processes (red-versus-green, blue-versus-yellow, black-versuswhite). Contemporary research has confirmed that, on the way to the brain, neurons in the retina and the thalamus code the color-related information from the cones into pairs of opponent colors. These two theories, and the research supporting them, show that color processing occurs in two stages.

How are our senses of taste and smell similar?

Both taste and smell are chemical senses. Taste involves five basic sensations— sweet, sour, salty, bitter, and umami. Taste receptors in the taste buds carry messages to an area between the frontal and temporal lobes of the brain. There are no basic sensations for smell. Some 20 million olfactory receptor cells for smell, located at the top of each nasal cavity, send messages to the brain. These cells work together, combining their messages into patterns that vary, depending on the different odors they detect.

What was the main message of Gestalt psychology, and how do figure-ground and grouping principles help us perceive forms?

Gestalt psychologists showed that the brain organizes bits of sensory information into gestalts, or meaningful forms. In pointing out that the whole may exceed the sum of its parts, they noted that we filter sensory information and construct our perceptions. To recognize an object, we must first perceive it as distinct (see it as a figure) from its surroundings (the ground). We bring order and form to sensory input by organizing it into meaningful groups, following such rules as proximity, continuity, and closure.

How do we use binocular and monocular cues to see the world in three dimensions?

Humans and many other species perceive depth at, or very soon after, birth. We transform two-dimensional retinal images into three-dimensional depth perceptions that allow us to see objects in three dimensions and to judge distance. Binocular cues, such as retinal disparity, are depth cues that rely on information from both eyes. Monocular cues (such as relative size, interposition, relative height, relative motion, linear perspective, and light and shadow) let us judge depth using information transmitted by only one eye.

What roles do feature detection and parallel processing play in the brain's visual information processing?

In the visual cortex, feature detectors respond to specific features of the visual stimulus, such as edges, lines, and angles. Through parallel processing, the brain handles many aspects of vision (color, movement, form, and depth) simultaneously. Other neural teams integrate the results, comparing them with stored information and enabling perceptions.

How does the eye transform light energy into neural messages?

Light entering the eye is focused on our retina—the inner surface of the eye. The retina's light-sensitive rods and color-sensitive conesconvert the light energy into neural impulses After processing by bipolar and ganglion cells in the eyes' retina, neural impulses travel through the optic nerve to the thalamus and on to the visual cortex.

How do absolute thresholds and difference thresholds differ, and what is Weber's law?

Our absolute threshold is the minimum stimulation needed for us to be consciously aware of any stimulus 50 percent of the time. (Stimuli below that threshold are subliminal.) A difference threshold (also called the just noticeable difference, or jnd) is the minimum change needed to detect a difference between two stimuli 50 percent of the time. Weber's law states that two stimuli must differ by a constant minimum percentage (rather than a constant minimum amount).

What three steps are basic to all our sensory systems?

Our senses (1) receive sensory stimulation (often using specialized receptor cells); (2) transform that stimulation into neural impulses; and (3) deliver the neural information to the brain. Transduction is the process of converting one form of energy into another.

How do our expectations, assumptions, contexts, and even our motivations and emotions affect our perceptions?

Perception is influenced by our perceptual set—our mental predisposition to perceive one thing and not another. Our physical, emotional, and cultural context, as well as our motivation, can create expectations about what we will perceive, thus affecting those perceptions.

What are sensation and perception? What do we mean by bottom-up processing and top-down processing?

Sensation is the process by which our sensory receptors and nervous system receive information and transmit it to the brain. Perception is the process by which our brain organizes and interprets that information. Bottom-up processing is analysis that begins with the sensory receptors and works up to the brain. Top-down processing is information processing guided by higher-level mental processing, such as when we construct perceptions by filtering information through our experience and expectations.

How do our senses interact?

Sensory interaction is the influence of one sense on another. This occurs, for example, when the smell of a favorite food enhances its taste. Embodied cognition is the influence of bodily sensations, gestures, and other states on cognitive preferences and judgments.

What are the characteristics of the energy we see as light?

The visible light we experience is just a thin slice of the broad spectrum of electromagnetic energy. The hue (blue, green, and so forth) we perceive in a light depends on its wavelength, and its brightness depends on itsintensity.

Can we be persuaded by subliminal stimuli?

We do sense some stimuli subliminally— less than 50 percent of the time—but those sensations don't have lasting behavioral effects.

What is the function of sensory adaptation?

We grow less sensitive to constant sensory input. This diminished sensitivity to constant or routine odors, sounds, and touches (sensory adaptation) focuses our attention on informative changes in our environment.