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Psychology (9,549)
PSYA01H3 (1,196)
Steve Joordens (1,052)
Chapter 4

Chapter 4 psych.docx

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University of Toronto Scarborough
Steve Joordens

4.1 Sensation and Perception at a Glance Sensation: the process of detecting external events by sense organs and turning those events into neural signals Perception: involves attending to, organizing and interpreting stimuli that we sense Transduction: The process in which physical or chemical stimulation is converted into a nerve impulse that is relayed to the brain Sensory adaptation: the reduction of activity in sensory receptors with repeated exposure to a stimulus Sensing the World around us - The body has an array of specialized processes that allow us to take all of this information in - First step is sensation. At the sensory level, the sound of someone’s voice is simply noise and the sight of a person is a combination of color and motion - Brain is where perception occurs - Perception includes recognizing the sounds as a human voice and understanding that the colors, shape and motion together make up the image of a human - Sensory receptors, structures that respond to external stimuli - The transduction of sound takes place in a specialized structure called the cochlea, where what we hear is converted into messages that travel to the hearing centers of the brain - Sensory adaptation allows us to adjust to our surroundings and shift our focus and attention to other events - William Gustav Fechner coined the term psychophysics Psychophysics: the field of study that explore how physical energy such as light and sound and their intensity relate to psychological experience Absolute threshold: The minimum amount of energy or quantity of a stimulus required for it to be reliably detected at least 50% of the time it is presented Difference threshold: the smallest detectable difference between stimuli The more intense the original stimulus, the more of it that must be added for the difference threshold to be reached SIGNAL DETECTION Signal detection theory: states that whether a stimulus is perceived depends on both sensory experience and judgment made by the subject - In the lab, the experimenter presents a faint stimulus or no stimulus at all (sensory process) and the subject is asked to report whether it was present ( the decision process) - False alarm; it could mean that you believed you heard a bear when there were none around PERCEVING THE WORLD AROUND US - The contours are referred to as subjective contours because they are not physically there GESTALT PRINCILES OF PERCEPTION - Mid 20 century, a school of psychology emerged out of Germany based on the work of individuals who sought to describe how we perceive form - Gestalt psychology is an approach to perception that emphasizes “ the whole is greater than the sum of its parts” - Another set of gestalt principles include proximity and similarity - Continuity, or good continuation refers to the perceptual rule that lines and other objects tend to be continuous, rather than abruptly changing direction - Closure refers to the tendency to fill in gaps to complete a whole object TOP- DOWN & BOTTOM- UP PROCESSING Top- down processing: occurs when prior knowledge and expectations guide what is perceived Bottom- up processing: constructing a whole stimulus or concept from bits of raw sensory Selective attention: involves focusing on one particular event or task, such as studying, driving without distraction Divided attention: involves paying attention to several stimuli or tasks at once - Top down processes can influence the perception of the image as well - Parallel processing refers to the simultaneous use of top-down and bottom-up processing as we perceive and interpret the world - It is what allows us to attend to multiple features of what we sense MISSING THE OBVIOUS: INATTENTIONAL BLINDNESS Inattentional blindness: a failure to notice clearly visible events or objects because attention is directed elsewhere - Inattentional blindness shows that when we focus on a limited number of features, we might not pay much attention to anything else 2.4 THE VISUAL SYSTEM The Human Eye - The eye senses array of information, and then relays it back to the brain for complex, perceptual processing How the light gathers light - The term light actually refers to radiation that occupies a relatively narrow band of the electromagnetic spectrum - Light travels in terms of two different properties: length and amplitude - Wavelength refers to the distance between peaks of a wave- differences in wavelength correspond to different colors on the electromagnetic spectrum - Long wavelengths correspond with the reddish colors and short wavelengths with the bluish colors - Low- amplitude waves correspond with dim colors and high amplitude with bright colors The Structure of the Eye Sclera: the white, outer surface of the eye Fovea: the part of the retina where light rays are most sharply focused Optic nerve: Transmits impulses from the retina to the visual centers of the brain Retina: Innermost layer of the eye, where incoming light is converted into nerve impulses Eye muscle: One of the six surrounding muscles responsible for rotating the eye Pupil: Opening in the center of the iris that lets in light Lens: Transparent disk that focuses light rays onto the retina Iris: Colored area containing muscles that regulate the size of the pupil Cornea: Curved, transparent dome that protects the eye and helps bend incoming light Rods: photoreceptors that occupy peripheral regions of the retina; they are highly sensitive under low light levels Cones: photoreceptors that are sensitive to the different wavelengths of light that we perceive as color Dark Adaptation: the process by which the rods and cones become increasingly sensitive to light under low levels of illumination - The eye consists of specialized structures that gather up this complex mixture of light hue, intensity, and saturation - These structures function to regulate the amount of light that enters the eye, and organize light into the eye and organize light into a pattern that the brain can interpret - Light enters the eye through the cornea and passes through an opening called the pupil - The pupil regulates the amount of light that enters by changing its size; it dilates to allow more light to enter and constricts to allow less light into the eye - The specialized receptors of the retina are called photoreceptors - Two general types of photoreceptors line the retina- rods and cones The Optic Nerve - Light stimulates chemical reactions in the rods and cones and these reactions initiate neural signals that pass through an intricate network of cells in the retina, which in turn send impulses to the brain - Blind spot is a space in the retina that lacks photoreceptors - The visual areas of the brain are able to ‘’fill in’’ the missing information for us Common Vision Disorders - Nearsightedness occurs when the eyeball is slightly elongated, causing the image that the cornea and lens focus on to fall short of the retina - If the length of the eye is shorter than normal from front to back the result is farsightedness in this case the image is focused behind the retina The Visual Pathways to the Brain - The information contained in the cells that constitute the optic nerve travels to numerous areas of the brain - The first major destination is the optic chiasm, the point at which the optic nerve cross at the midline of the brain - For each optic nerve, about half of the nerve fibers travel to the same side of the brain, and half of them travel to the opposite side - Fibers from the optic nerves first connect with the visual area of the thalamus at a region called the lateral geniculate nucleus - The LGN sends messages to the visual cortex, located in the occipital lobe, where the complex processes of visual perception begin - One set of cells in the visual cortex are referred to as feature detection cells; they respond selectively to simple and specific aspects of a stimulus, such as angles and edges Perceptual constancy: The ability to perceive objects as having constant shape, size and color despite changes in perspective - The ventral stream is a pathway extending from the visual cortex to the temporal lobe and is where object recognition occurs - The dorsal stream extends from the visual cortex to the parietal lobe of the cortex and is where depth and motion are perceived - Feature detection cells of the visual cortex are thought to be where visual input is organized for perception, but further processing is require as well and involves additional neural pathways The Visual Experience - Our visual experiences arise from higher brain centers of the cerebral cortex Facial recognition and perception - There is a region of the brain, located in the lower part of the temporal lobe, that is specialized for facial recognition - Some people with face blindness can find ways to compensate for the condition, such as developing heightened abilities to use voice recognition and other non facial cues for recognizing individuals - We rely on the unique characteristics of the eyes and mouth most when we recognize a familiar face Depth Perception Binocular depth cues are distance cues that are based on the differing perspective of both eyes Convergence: occurs when the eye muscle contract so that both eyes focus on an single object Retinal disparity: the difference in relative position of an object as seen by both eyes, which provides information to the brain bout depth Monocular cues are depth cues that we can perceive with only one eye Depth Perception - The sensations that occur as these muscles contract to focus on a single object create the perception of depth -Stereoscopic vision, which results from
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