Perception & Consciousness

Perception & Consciousness Unit 2

How Do We Sense Our Worlds? Learning Objectives • Distinguish between sensation and perception. • Describe the process of transduction. • Distinguish between an absolute threshold and a difference threshold. • Discuss sensory detection theory. • Define sensory adaptation.

How Do We Sense Our Worlds? • Sensation:our sense organs’ detection and response to external stimulus energy and the transmission of those responses to the brain • Perception:the brain’s processing of detected signals, resulting in internal representations of the stimuli that form a conscious experience of the world • What we sense is the result of how we perceive

Stimuli Must Be Coded to Be Understood by the Brain • Sensory coding: Sensory receptors translate the physical properties of stimuli into patterns of neural impulses • Transduction:a process by which sensory receptors produce neural impulses when they receive physical or chemical stimulation • The brain needs qualitative and quantitative information about a stimulus • Sensation and perception result from a symphony of sensory receptors and the neurons those receptors communicate with

Psychophysics Measures the Relationship between Stimuli and Perception • Psychologists try to understand the relationship between the world’s physical properties and how we sense and perceive them • Psychophysics is a subfield that examines our psychological experiences of physical stimuli

Sensory Adaptation • Sensory adaptation: a decrease in sensitivity to a constant level of stimulation • If a stimulus is presented continuously, the responses of the sensory systems that detect it tend to diminish over time; when a continuous stimulus stops, the sensory systems usually respond strongly as well

What Are the Basic Sensory Processes? • For each of the five major senses — taste, smell, touch, hearing, and vision — identify the type of receptor and trace the neural pathway to the brain • Distinguish between the neural processes associated with the experience of immediate pain and the experience of chronic pain • Discuss color perception

Taste Buds • Gustation:the sense of taste • Taste buds: sensory organs, mostly on the tongue; come in the form of tiny, mushroom-shaped structures (papillae) • Stimulated taste buds send signals to the brain, which then produces the experience of taste • Different regions of the tongue are not more sensitive to certain tastes (Lindemann, 2001) • Every taste experience is composed of a mixture of five basic qualities: sweet, sour, salty, bitter, and the relatively new taste sensation umami (Krulwich, 2007) • Mothers can pass their eating preferences on to their offspring

Nasal Cavity • Olfaction: the sense of smell • Basic process: • Odorants pass into the nose and nasal cavity • Contact a thin layer of tissue embedded with smell receptors called the olfactory epithelium • Smell receptors transmit information to the olfactory bulb, the brain center for smell • Has the most direct route to the brain • Smell’s intensity is processed in brain areas also involved in emotion and memory (Anderson, Christoff et al., 2003)

Skin • Haptic sense: the sense of touch • Sense conveys sensations of temperature, pressure, pain, and where our limbs are in space • The integration of various signals and higher-level mental processes produces haptic experiences • Examples: • Stroking multiple pressure points can produce a tickling sensation, which can be pleasant or unpleasant, depending on the mental state of the person being tickled • Brain areas involved in touch sensation respond less to self-produced tactile stimulation than to external tactile stimulation (Blakemore, Wolpert, & Frith, 1998)

Two Types of Pain • Pain is part of a warning system that stops you from continuing activities that may harm you • Two kinds of nerve fibers have been identified for pain: • Fast fibers for sharp, immediate pain; activated by strong physical pressure and temperature extremes • Slow fibers for chronic, dull, steady pain; activated by chemical changes in tissue when skin is damaged

Ear • Audition: the sense of sound • Movements and vibrations of objects cause the displacement of air molecules, which produce a sound wave (change in air pressure that travels through the air) • A sound wave’s amplitude determines loudness; its frequency determines pitch • The ears convert sound waves to brain activity, which produces the sensation of sound

Eye • Most of the scientific study of sensation and of perception is concerned with vision • Very little of what we call seeing takes place in the eyes, but rather as a result of constructive processes that occur throughout much of the brain • Basic structures: cornea, lens, pupil, iris, retina

What Factors Influence Visual Perception? • Describe the Gestalt principles of perceptual organization. • Identify the brain regions associated with facial perception. • Identify cues for depth perception. • Explain how the visual system perceives motion. • Discuss how perceptual constancy is achieved.

Object Perception Requires Construction • Perceptual psychologists believe that illusions reveal the mechanisms that help our visual systems determine the sizes and distances of objects in the visual environment • Researchers rely on these tricks to reveal automatic perceptual systems that, in most circumstances, result in accurate perception

Gestalt Principles of Perceptual Organization • The German word Gestalt means “shape” or “form.” As used in psychology, Gestalt means “organized whole.” • Gestalt psychology postulated a series of laws to explain how our brains group the perceived features of a visual scene into organized wholes

Figure and Ground • Among the most basic organizing principles is distinguishing between figure and ground • A classic illustration of this is the reversible figure illusion, in which figure and ground switch back and forth (ambiguous) • In identifying what is “figure,” the brain assigns the rest of the scene to the background

Proximity and Similarity • Two of the most important Gestalt principles concern proximity and similarity • Principle of proximity:The closer two figures are to each other, the more likely we are to group them and see them as part of the same object • Principle of similarity: We tend to group figures according to how closely they resemble each other

The “Best” Forms • Good continuation: the tendency to interpret intersecting lines as continuous rather than as changing direction radically • Closure: the tendency to complete figures that have gaps • Illusory contours: We sometimes perceive contours and cues to depth even though they do not exist

Bottom-Up and Top-Down Information Processing • How do we assemble the information about parts into a perception of a whole object? • Bottom-up processing: Data are relayed in the brain from lower to higher levels of processing • Top-down processing: Information at higher levels of mental processing can influence lower, “earlier” levels in the processing hierarchy • The flight crew of New Zealand Flight 901 failed to notice the 12,000-foot volcano looming in front of them because the pilots saw what they expected to see

Face Perception • The visual system is sensitive to faces: • We can more readily discern information about a person’s mood, attentiveness, sex, race, and age by looking at a person’s face than by listening to them talk, watching them walk, or studying their clothing (Bruce & Young, 1986) • Whites are much better at recognizing white faces than at recognizing black faces (Brigham & Malpass, 1985) • Prosopagnosia:deficits in the ability to recognize faces • Cortical regions, even specific neurons, seem to be specialized to perceive faces and are sensitive to facial expression and gaze direction

Ames Boxes • Ames boxes: first crafted in the 1940s by Adelbert Ames, a painter turned scientist • Ames boxes’ rooms play with linear perspective and other distance cues to create size illusions

The Ponzo Illusion • Classic example of a size/distance illusion • Explained: Monocular depth cues make the two-dimensional figure seem three-dimensional (Rock, 1984) • This illusion shows how much we rely on depth perception to gauge size; the brain uses depth cues even when depth is absent

Consciousness • Erik Ramsey is “locked in…” • Suffered traumatic injury to his brain as the result of an automobile accident • He can see, hear and feel, but he cannot move or communicate with the outside world…at least not yet

Consciousness • In a coma, but aware • Patterns of brain activity in a coma sufferer were similar to patterns found in those not in a coma (Owen et al., 2006) • Communication may be possible with coma patients previously believed to be unreachable

Perception & Consciousness