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Chapter 6.docx

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Wilfrid Laurier University
Todd Ferretti

Chapter 6 Sensory and Perception Sensation and Perception  Sensation o The detection of physical energy emitted or reflected by physical objects o Occurs when energy in the external environment or the body stimulates receptors sin the sense organs  Perception o Process by which the brain organizes and interprets sensory information Separate Sensations  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 o Dendrites of sensory neurons responsible for smell, pressure, pain and temperature o Specialized cells for vision, hearing, taste  Doctrine of specific nerve energies (Muller) o Principle that different sensory modalities exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain o If possible, allows for sensory substitution o Sensory crossover also occurs in synaesthesia where stimulation of one sense consistently evokes a sensation in another Measuring the Senses  Psychophysics o Field concerned with how the physical properties of stimuli are related to our psychological experiences of them o Commonly relies on measuring absolute threshold, difference threshold, and applying signal-detection theory  Absolute Threshold o The smallest quantity of physical energy that can be reliably detected by an observer (50% of the time) o Senses are sharp , but only tuned into narrow band of physical energies  Difference Threshold o The smallest difference in stimulation that can reliably be detected by an observer when two stimuli are compared o Has to be a noticeable enough difference, depends on ratio with regards to context of whatever else is happening o Also called just noticeable difference (JND) o Weber's law: size of JND proportional to size of initial stimulus o JND for weight is 1/30  Signal Detection Theory o Divides the detection of sensory signals into a sensory process and a decision process o False alarm is type 1 error (false positive) o Miss is type 2 error (false negative) Sensory Adaptation and Depravation  Sensory Adaptation o Reduction of disappearance of sensory responsiveness when stimulation is unchanging or repetitious o Useful as it spares us from responding to unimportant information  Sensory Deprivation o The absence of normal levels of sensory stimulation o Varied responses somewhat dependent on expectations and interpretations (e.g. hallucinations) Sensing Without Perceiving  Selective Attention o Focusing of attention on selected aspects of the environment and blocking out the others  Intentional Blindness o Failure to consciously perceive something you are looking at because you are not attending to it Vision: The Stimulus  Light = electromagnetic radiation o Amplitude: perception of brightness o Wavelength: perception of colour o Purity: mix of wavelengths -perception of saturation, or richness of colours  Light stimuli (waves) have physical characteristics that affect three psychological dimensions of our visual world: 1. Hue o Dimension of visual experience specified by colour names o Related to the wavelength of light 2. Brightness o Dimension of visual experience related to the amount of light emitted from or reflected by an object o Related to amplitude of wavelength 3. Saturation o Dimension of visual experience related to the complexity of light waves o Vividness or purity of colour Eye  Cornea: Protects the eye and bends light towards lens  Lens: Focuses on objects by changing shape  Iris: Controls amount of light that gets into eye  Pupil: Widens or dilutes to let in more light Visual Receptors  Retina o Neural tissue lining the back of the eyeballs interior which contains the receptors for vision o Rods: visual receptors that respond to dim light -120-125 million, concentrated in the periphery of the retina o Cones: visual receptors involved in colour vision -7-8 million, concentrated in the centre of the retina (fovea) -Low sensitivity (used for day vision) -Sensitive to colour The Retina  We experience chemical changes in rods and cones when our eyes adjust fully to dim illumination ( called dark adaptation)  Retinal processing also involved ganglion cells o Neurons in the retina that gather information from receptor cells (by the way of intermediary bipolar cells) o Axons from the optic nerve which leaves the eye at the optic disk (location of blind spot) Vision Is Not Like A Camera  Visual processing is an active process and involves many types of cells in different brain regions o Cortical cells respond to lines of specific orientations, others respond to properties of shapes and arrangements (e.g. spirals, faces, greebles)  Visual Detector Cells o Cells in the visual cortex that are sensitive to specific features of the environment Constructing the Visual World  We rely on various Gestalt principles to organize visual input o Similarity: occurs when objects look similar to one another, perceived as a group or pattern o Continuation: occurs when the eye is compelled to move through one object and continue to another object; o Closure: occurs when an object is incomplete or a space is not completely enclosed; when viewers perception becomes a shape, closure occurs o Proximity: occurs when elements are placed together; tend to be perceived as a group  Figure: item of interest that stands out from the rest of the environment  Ground: Environment or background Depth and Distance Perception  Visual system relies on two types of cues to judge where an object is, and how far away from us it is o Binocular Cues: used for objects that are fairly close to us o Monocular Cues: used when objects are far away Binocular Cues  Binocular cues provide visual cues to depth or distance requiring two eyes o Convergence: the turning inward of the eyes, which occurs when they focus on a nearby object o Retinal Disparity: the slight difference in lateral separation between two objects as seen by the left eye and the right eye Monocular Cues  Monocular cues are visual cues to depth or distance that can be used by one eye alone o Light and shadow, interposition, Motion parallax, Linear perspective, Relative size, Relative clarity, and Texture gradients (p 205-207) o Light and Shadow: Both of these attributes give objects the appearance of three dimensions o Interposition: An object that partly blocks or obscures another one must be in front of the other one and is therefore seen as closer o Motion Parallax: Closer an object faster it seems to move; close objects appear to move backwards, while distant objects appear to move forward o Relative Size: Smaller an objects image on retina, farther away it appears o Relative Clarity: Because of particles in air, distant objects look hazier, duller, etc o Texture Gradients: Distant parts of uniform surface appear denser; i.e. closer together o Linear Perspective: Parallel lines appear to converge in distance; more perceived convergence greater perceived distance  Perception of distance also affected by emotional factors Visual Constancies  Another important perceptual skill is perceptual constancy o The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce o Best-studied are shape, location, size, brightness, and colour constancies o Context Effects: The context in which a stimulus is seen can affect your perpetual hypotheses How We See Colour  Trichromatic Theory o Proposes three basic types of cones, each sensitive to a certain range of wavelengths
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