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Chapter 6

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Wilfrid Laurier University
Kathy Foxall

Chapter 6:Sensation and Perception Our Sensational Senses The Riddle of Separate Sensations  Sensation o Detection of physical energy emitted or reflected by physical objects; occurs when energy in the environment or the body stimulates receptors in the sense organs  Perception o The process by which the brain organizes and interprets sensory information  Sense receptors o Specialized cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain  Smell, pressure, pain, extensions of sensory neurons  Vision, hearing, and taste specialized cells separated from neurons by synapses  Steps of conversion o Scouts/receptors scan for activity o Transmit what they learn to field officers/sensory neurons o Report to command centre of generals/cells of the brain, determine what it all means  Sensory nerves use exactly the same form of communication  Doctrine of specific nerve energies o The principle that different sensory modalities exist because signals received by sense organs stimulate different nerve pathways leading to different areas of the brain  Synesthesia o Condition in which stimulation of one sense evokes another o More a perceptual crossover than sensory, associated more with meaning  Criticism that nerve energy fails to explain variations within a sense Measuring the Senses  Absolute threshold o The smallest quantity of physical energy that can be reliably detected by an observer  Difference thresholds o The smallest difference in stimulation that can be reliably detected by an observer when two stimuli are compared; also called just noticeable difference o The larger or more intense A, the greater the change must be to detect a difference Signal Detection Theory  Psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision process  Sensory process o Depends on intensity of stimulus  Decision process o Influenced by the observer’s response bias Sensory Adaptation  The reduction or disappearance of a sensory responsiveness when stimulation is unchanging or repetitious  Receptor nerves get tired and fire less frequently  Rarely adapt however o Eye movements change the location of an object on the back of the eye to keep changing  Sensory deprivation o The absence of normal levels of sensory stimulation o Depends on expectations and interpretations of what is happening, still required minimum amount of stimulation to function normally Sensing without perceiving  Cocktail party phenomenon o Person typically focuses on just one conversation, ignoring other voices  Selective attention o Focusing of attention on selected aspects of the environment and the blocking out of others  Inattentional blindness o Failure to consciously perceive something you are looking at because you are not attending to it Vision What we See  Light travels in waves, physical characteristics affect three psychological dimensions of our visual world: hue, brightness, and saturations  Hue o The dimension of visual experience specified by colour names and related to the wavelength of light  Brightness o Lightness or luminance; the dimension of visual experience related to the amount of light emitted from or reflected by an object o Intensity corresponds to wave height o The more light, the brighter it appears, also affected by wavelength  Saturation o Vividness or purity of colour; the dimension of visual experience related to the complexity of light waves o Single wavelength pure, full saturation and colour o White light lacks colour, unsaturated An eye on the world o Cornea covers front part of the eye, protects it and bends light rays toward lens located behind it o Lens of eye work by changing shape, becoming more or less curved to focus light o Iris o Gives eye its colour, surrounds pupil o Muscle that controls light into eye o Pupil o Opening of the eye o Retina o Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision o Extension of the brain o How Lens work o Focus light on retina in upside down image o Light from top of field stimulates light sensitive receptor cells in bottom of the retina, vice versa o Rods o Visual receptors that respond to dim light o More sensitive to light than cones o Cones o Visual receptors involved in colour vision o Focused on centre of retina o Need more light to see colours, o Dark adaptation o Process by which visual receptors become maximally sensitive to dim light o Ganglion cells o Neurons in the eye that gather info from receptor cells; axons make up optic nerve o Absence of receptors at optic nerve produce blind spot Why the Visual system is not a camera  Feature detector cells o Cells in the cortex that are sensitive to specific features of the environment  David hubel and wiesel o Different neurons sensitive to different patterns projected on a screen in front of animal’s eyes o E.g. cells respond to moving/stationary lines How we see colours  Trichromatic theory o Theory of colour perception that proposes three mechanisms in the visual system, each sensitive to a certain range of wavelengths; their interaction is assumed to produce all the different experiences of hue o First level of processing containing three basic cones o Colour deficient, unable to distinguish between colours  Opponent Process Theory o Theory of colour perception that assumes the visual system treats pairs of colours as opposing or antagonistic o Respond in opposite fashion to red and green, blue and yellow, and white and black o Act antagonistic Constructing the visual world Form Perception  Gestalt Psychologists o Perceive something as a whole o Organize into figure and ground o Figure  Stands out by virtue or intensity of size  Depend on experience,  Gestalt Principles o Principles that describe the brain’s organization of sensory information into meaningful units and patterns  Proximity  Group things together  Closure  Fill gaps in order to perceive complete forms  Similarity  Perceived as belonging together  Continuity  Depth and Distance perception o Binocular cues  Visual cues to depth or distance requiring two eyes o Convergence  Turning inward of eyes, occurs when they focus on a nearby object o Retinal disparity  Slight difference in lateral separation between two objects as seen by left
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