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Department
Psychology
Course
PSYC 1010
Professor
All Professors
Semester
Winter

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Chapter 4: Sensation and Perception - a lot of research done on space shuttles - There may be discontinuity between sensory information derived from the vestibular system (organs in the inner ear) and visual cues - Ian Howard - involved in space research and known internationally as a pioneer in sensation/perception research - Normal people can rely on 3 different types of cues to determine which way is up: visual, gravity and body direction - sensation - the simulation of sense organs - perception - the selection, organization and interpretation of sensory input KEY POINTS IN THIS CHAPTER (pages 127-130) - Psychophysicist use a variety of methods to relate sensory inputs to subjective perception. They have found that absolute thresholds are not really absolute - Weberʼs law states that the size of a just noticeable difference is a constant proportion of the size of the initial stimulus. Gechnerʼs law asserts that larger and larger increases in stimulus intensity are required to produce just noticeable differences in the magnitude of sensation - According to signal-detection theory, the detection of sensory inputs is influenced by noise in the system and by decision-making strategies. Signal-detection theory replaces Fechnerʼs sharp threshold with the concept of detectability and emphasis that factors besides stimulus intensity influence detectability - In recent years, a host of researchers, using very different conceptual approaches, have demonstrated that perception can occur without awareness. However, research indicates that the effects of subliminal perception are relatively weak and of little or no practical concern - Prolonged stimulation may lead to sensory adaption, which involves a reduction in sensitivity to constant simulation Psychophysics: Basic Concepts and Issues - psychophysics - the study of how physical stimuli are translated into psychological experience Thresholds: Looking for Limits - sensation begins with a stimulus - any detectable input from the environment - threshold - a dividing point between energy levels that do or do not have a detectable effect - An absolute threshold for a specific type of sensory input is the minimum amount of stimulation that an organisms can detect - Fechner and his contemporaries used a variety of methods to determine humansʼ absolute threshold for detecting light - found that no single stimulus intensity at which the subject jumps from no detection to completely accurate detection, instead as stimulus intensity increases, subjectsʼ probability of responding to stimuli gradually increases - researchers defined the absolute threshold as the stimulus intensity detected 50% of the time Chapter 4: Sensation and Perception Weighing the Differences: The JND - Fechner was also interested in peopleʼs sensitivity to differences between stimuli - Just noticeable difference (JND) - the smallest difference in the amount of stimulation that a specific sense can detect - Weberʼs law - states that the size of a JND is a constant proportion o the size of the initial stimulus - this constant proportion is called Weber fraction - As stimulus increase in magnitude the JND becomes larger Psychophysical Scaling - Fechnerʼs Law - states that the magnitude of a sensory experience is proportional to the number of JNDs that the stimulus causing the experience is above absolute threshold - constant increments in stimulus intensity produce smaller and smaller increases in the perceived magnitude of sensation - perceptions canʼt be measured on absolute scales. In the domain of sensory experience, virtually everything is relative Signal-Detection Theory - Signal-detection theory - proposes that the detection of the stimuli involves decision processes as well as sensory processes, which are both influenced by a variety of factors besides stimulus intensity - four outcomes possible in attempting to detect the presence of weak signals: - hits (detecting signals when they are present) - misses (failing to detect signals when they are present) - false alarms (detecting signals when they are not present) - correct rejections (not detecting signals when they are absent) - your performance depends on the level of “noise” in the system - noise comes from all irrelevant stimuli in the environment and the neural activity they elicit Perception without Awareness - subliminal perception - the registration of sensory input without conscious awareness - the dominant view today is that subliminal perception is a genuine phenomenon that is worthy of experimental investigation - subliminal stimulation generally produces weak effects Sensory Adaption - sensory adaption - a gradual decline in sensitivity to prolonged stimulation - automatic, built-in process that keeps people tuned in to the changes rather than the constants in their sensory input - allows people to ignore the obvious and focus on changes in their environment that may signal threats to safety - likely sculpted by natural selection Chapter 4: Sensation and Perception KEY POINTS IN THIS CHAPTER (pages 131-139) - Light varies in terms of wavelength, amplitude, and purity. Light enters the eye through the cornea and pupil and focused upside down on the retina by the lens. Distant objects appear blurry to nearsighted people and close objects appear blurry to farsighted people. - The retina is the neural tissue in the eye that absorbs light processes images, and a sends visual signals to the brain. Cones, which are concentrated in the fovea, play a key role in daylight vision and colour perception. Rods, which have their greatest density just outside the fovea, are critical to night vision and peripheral vision. Dark adaption and light adaptation both involve changes in the retinaʼs sensitivity to light, allowing the eye to adapt to changes in illumination - The retina transforms light into neural impulses that are sent to the brain via the optic nerve. Receptive fields are areas in the retina that affect the firing of visual cells. They are vary in shape and size, but centre-surround arrangements are common. The optic nerves from the inside half of each eye cross at the optic chiasm and then project to the opposite half of the brain - Nobel Prize-winning research by Hube and Wiesel suggests that the visual cortex contains cells that function as feature detectors The discovery of the what pathway and the neurons inside it that respond specifically to faces have shed new light on visual disorders that have perplexed scientists for decades - Vision researchers employ multiple, converging methods when trying to explain the role of the brain in visual experience. This was illustrated with recent research on the McCollough effect. Our Sense of Sight: The Visual System The Stimulus: Light - light is a form of electromagnetic radiation that travels as a wave, moving naturally enough, at the speed of light - light waves vary in amplitude (height) and in wavelength (the distance between peaks) - amplitude affects perception of brightness - wavelength affects perception of colour - Light can vary in its purity (ow varied the mixture of several wavelengths is) - purity influences perception of the saturation, or richness, or colours - Most objects reflect light - The visual spectrum is only a slim portion of the total range of wavelengths - for people to see, incoming visual input must be converted int oneural impulses that are sent to the brain The Eye: A Living Optical Instrument - Eyes (1) channel light to the neural tissue that receives it, call the retina (2) they house that tissue - Light enters the eye through the cornea. The transparent cornea and the lens located behind it for an upside-down image of objects on the retina - lens - transparent eye structure that focuses the light rays falling on the reina - lensʼs soft tissue is capble of adjusting in order to facilitate accomindation - occurs - when the curvature of the lens adjusts to alter visual focus Chapter 4: Sensation and Perception - Deficiencies caused by focusing problems - Nearsightedness - close objects are seen clearly but distance objects appear blurry - focus from light from distance objects falls a little short of the retina - the cornea or lens bends light too much or when eyeball is too long - Farsightedness- distant objects are seen clearly but close objects appear blurry - focus from light from close objects falls behind the retina - when eyeball is too short - iris - coloured ring of muscle surrounding the pupil - pupil - the opening in the centre of the iris that helps regulate the amount of light passing into the rear chamber of the eye. - when pupil constricts, let in less light but more sharpness of images The Retina: Brainʼs Envoy in the Eye - retina - the neural tissue lining the inside back surface of the eye; it absorbs light, processes images and sends visual information to the brain - paper-thin sheet of neural tissue which contains a complex network of specialized cells arranged in layers. - retina processes images - piece of the CNS located in the eyeball - brainʼs envoy to the eye - axons that run from the retina to the brain converge at the optic disk - a hole in the retina where the optic nerve fibres exit the eye - since hole, canʼt see the part of the image that falls on i therefore it is the blind spot - each eye compensates for the blind spot in the other eye VISUAL RECEPTORS: Rods and Cones - retinaʼs receptor cells located in the innermost layer of the retina - retina contains two types of receptors (1) Rods (elongated) (2) Cones (stubbier) - Cones - specialized visual receptors that play a key role in daylight vision and colour vision - provide better visual acuity - sharpness and precise detail - than rods - concentrated most heavily in centre of the retina - Fovea - a tiny spot in the centre of the retina that contains only cones; visual acuity is greatest at this spot - Rods - specialized visual receptors that play a key role in night vision and peripheral vision - outnumber cones in periphery of the retina - greatest number just ouside of the fovea DARK AND LIGHT ADAPTION - dark adaption - the process in which the eyes become more sensitive to light in low illumination - light adaption - the process whereby the eyes become less sensitive to light in high illumination - Both types of adaption are due in large part to the chemical changes in the rods and cones, but neural changes in the receptors and elsewhere in the retina also contribute Chapter 4: Sensation and Perception INFORMATION PROCESSING IN THE RETINA - retina transforms a pattern of light falling onto it into a very different representation of the visual scene. - light striking itʼs receptors triggers neural signals that pass into the intricate network of cells in the retina which then send impulses along the optic nerve - a collection of axons that connect the eye with the brain - receptive field of a visual cell - the retinal area that , when stimulated, affects the firing of that cell - come in different shapes and sizes - When receptive fields are stimulated retinal cells send signals both toward the brain and laterally (sideways) toward nearby visual cells which allow visual cells in the retina to have interactive effects on each other - Lateral antagonist is the most basic one of these interactive effects - Lateral antagonism - occurs when neural activity in a cell opposes activity in surrounding cells. - allows the retina to compare the light falling in a specific area against general lighting - attention to contrast Vision and the Brain VISUAL PATHWAYS TO THE BRAIN - visual information gets to the brain by... - axons leaving the back of each eye for the optic nerves, which travel to the optic chiasm - the point at which the optic nerves from the inside half of each eye cross over and then project to the opposite half of the brain --> insures that signals from both eyes go to both hemispheres of the brain - after reaching the optic chiasm, the optic nerve fibres diverge along two pathways. --> the main pathway projects into the thalamus, the brainʼs major relay station. 90% of the axons from the reinas synaps in the lateral geniculate nucleus (LGN) where visual signals are processed and then distributed to areas in the occipital lobe that make up the primary visual cortex - the second pathway branches off an area in the midbrain called the superior colluculus before travelling through the thalamus and on to the occipital lobe - principle function of second pathway appears to be the coordination of visual input with other sensory input - Main visual pathway is subdivided into two more specialized pathways called the magnocellular (processes information) and parvocellular (handles the perception of colour) channels - these channels engage in parallel processing - involves simultaneously extracting different kinds of information from the same input INFORMATION PROCESSING IN THE VISUAL CORTEX - most visual input eventually arrives in the primary visual cortex located in the occipital lobe - “ Nobel Prize-winning research by Hube and Wiesel suggests that the visual cortex contains cells that function as feature detectors The discovery of the what pathway and the neurons inside it that respond specifically to faces have shed new light on Chapter 4: Sensation and Perception visual disorders that have perplexed scientists for decades” - discovered that individual cells i the primary visual cortex donʼt really respond much to little spots- they are much more sensitive to lines, edges and other more complicated stimuli - identified various types of specialized cells in the primary visual cortex that respond to different stimuli - the cells in the visual cortex seem to be highly specialized - feature detectors - neurons that respond selectively to very specific features of more complex stimuli - significant disruption in visual input for humans early in their lives might lead to permanent perceptual deficits - As signals move further along the visual processing system, neurons becoem even more specialized or fussy about what turns them on and the stimuli that activate them become more and more complex - visual agnosia - an inability to recognize objects MULTIPLE METHODS IN VISION RESEARCH - Include contemporary technologies such as fMRI as well as classic techniques such as observing the performance of individuals who have suffered specific types of brain damage. - “Vision researchers employ multiple, converging methods when trying to explain the role of the brain in visual experience. This was illustrated with recent research on the McCollough effect. KEY POINTS IN THIS CHAPTER (pages 140-148) - Perceptions of colour (hue) are primarily a function of light wavelength, while amplitude affects brightness and purity affects saturation. There are two types of colour mixing: additive and subtractive. Human colour perception depends on processes that resemble additive colour mixing - The trichromatic theory holds that people have three types of receptors that are sensitive to wavelengths associated with red, green, and blue. The opponent process theory hold that colour perception depends on receptors that make antagonistic responses to red versus green, blue versus yellow and black versus white. The evidence now suggests that both theories are necessary to account for colour vision - Reversible figures and perceptual sets demonstrate that the same visual input can result in very different perceptions. Form perception depends on both the selection and interpretation of the sensory inputs. According to feature analysis theories, people detect specific elements in stimuli and build them into recognizable forms through bottom-up processing. However, form perception also involves top-down processing, which progresses from the whole to the elements - Gestalt psychology emphasized that the whole may be greater than the sum of its parts (features), as illustrated by the Gestalt principles of form perception, including figure-ground, proximity, similarity, continuity, closure, and simplicity. Other approaches to for perception emphasize that people develop perceptual hypotheses about the distal stimuli that could be responsible for the proximal stimuli that are sensed Chapter 4: Sensation and Perception Viewing the World in Colour THE STIMULUS COLOUR - lights people see are mixtures of various wavelengths - colour is a psychological interpretation, not a physical property of light itself - Two kinds of colour mixture: subtractive and additive - Subtractive colour mixing - works by removing some wavelengths of light, leaving less light than was originally there - Additive colour mixing - works by superimposing lights, putting more light in the mixture than exists in any one light by itself TRICHROMATIC THEORY OF COLOUR VISION - First stated by Thomas Young and modified later by Hermann von Helmholtz - Trichromatic theory of colour vision - holds that the human eye has three types of receptors with different sensitivities to different light wavelengths - Helmholtz: eye contains specialized receptors for red, green and blue - Colour blindness - encompasses a variety of deficiencies in the ability to distinguish among colours - most are dichromats - make due with 2 out of the 3 colour channels OPPONENT PROCESS THEORY OF COLOUR VISION - Complementary colours - are pairs of colours that produce grey tones when mixed together - afterimage - a visual image that persists after a stimulus is removed - the colour of the afterimage will be the complement of the colour you originally stared at - trichromatic theory cannot account for this - Ewald Hering proposed the opponent process theory - (of colour vision) holds that colour perception depends o receptors that make antagonistic responses to three pairs of colours - the three pairs of opponent colours: red vs. green, yellow vs. blue and black vs. white - Also explains why dichromats find it hard to distinguish either green from red or yellow from blue RECONCILING THEORIES OF COLOUR VISION - argued that one theory must be wrong and the other right - It takes both colour theories to explain colour vision - George Wald (Nobel Prize) demonstrated that the eye has three types of cones with each type being most sensitive to a different band of wavelengths - the three different colour cones represent the three different colour receptors predicted in the trichromatic theory - Researchers found cells in the retina, the LDN and the visual cortex that respond in opposite ways to red versus green and blue versus yellow Chapter 4: Sensation and Perception Perceiving Forms, Patterns, and Objects - reversible figure - a drawing that is compatible with two interpretations that can shift back and forth - the same visual input can result in radically different perception - principle reason why peopleʼs experience of the world is subjective - perceptual set - a readiness to perceive a stimulus in a particular way - inattention blindness - involves the failure to see fully visible objects or evens in a visual display Study - watched video- had to focus on when a team passed a ball - when a woman with and umbrella and a person in a gorilla suit passed, most didnʼt notice - has been attributed to subjects having a perceptual set that leads them to focus most of their attention on specific feature in a scene while neglecting other facets of the scene FEATURE ANALYSIS: Assembling Forms - feature analysis - the process of detecting specific elements in visual input and assembling them into a more complex form - Feature analysis assumes that form perception involves bottom-up processing - a progression from individual elements to the whole - Hubel and Wiesel showed that cells in the visual cortex operate as highly specialized feature detectors - problem with theory - form perception often does not involve bottom-up processing - a lot of evidence that perceptions of form frequently involve top-down processing - a progression from the whole to the elements - phenomenon traditionally attributed to top-down processing: - reading - ability to perceive a word before its individual letters - subjective contour - the perception of contours where none actually exist ** although now view that it is top-down processing since researchers have shown that feature detectors do respond to the edges in subjective contours LOOKING AT THE WHOLE PICTURE: Gestalt Principles - Gestalt psychology is an influential school of thought mentioned in chapter 1 - demonstrated that the whole can be greater than the sum of its parts - phi phenomenon first described by Max Wertheimer - the illusion of movement created by presenting visual stimuli in rapid succession - The Gestalt psychologists formulated a series of principles that describe how the visual system organizes a scene into discrete forms: * Figure and Ground - Dividing visual displays into figure and ground is a fundamental way in which people organize visual perceptions - the figure is the thing being looked at and the ground is the background against which it stands - Figures seem to have more substance and shape, appear closer to the viewer and seem to stand out in from of the ground Chapter 4: Sensation and Perception Proximity -Things near each other seem to belong together Closure - people often group elements to create a sense of closure or completeness - may “complete” figures that actually have gaps in them Similarity - People tend to group stimuli that are similar Simplicity - The Gestaltistsʼ most general principle was the law of Pragnanz, which translates from German as “good form”. - People tend to group elements that combine to form a good figure - Some theorists maintain that goodness is largely a matter of simplicity, asserting that people tend to organize forms in the simplest way possible Continuity - People tend to follow in whatever direction theyʼve been led - people tend to connect points that result in a straight or gently curved lines that create “smooth” paths Gestalt psychology, although no longer an active theoretical orientation in modern psych, it raised many important questions that still occupy researchers FORMULATING PERCEPTUAL HYPOTHESES - Understanding how organized visual input results in a representation of the real world requires distinguishing between two kinds of stimuli: distal and proximal - Distal stimuli - stimuli that lie in the distance (in the world outside the body) - what your eyes donʼt touch - Proximal stimuli - stimulus energies that impinge directly on sensory receptors - images formed by patterns of li
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