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Sensation and Perception.docx

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Lawrence Murphy

Sensation and Perception Sensation  The detection of physical energy emitted or reflected by physical objects  Occurs when energy in the external environment or the body stimulates receptors in the sense organs Perception  Processes by which the brain organizes and interprets sensory information (“I am writing”) Separate Sensations? Sense receptors  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  Dendrites of sensory neurons responsible for smell, pressure, pain, & temperature  Specialized cells for vision, hearing, taste Doctrine of specific nerve energies (Muller)  Principle that different sensory modalities exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain  If possible, allow for sensory substitution  Sensory crossover also occurs in synesthesia where stimulation of one sense consistently evokes a sensation in another Measuring the Senses Psychophysics  Field concerned with how the physical properties of stimuli are related to our psychological experience of them  Commonly relies on measuring absolute threshold, difference threshold, and applying single- detection theory Absolute Threshold  The smallest quantity of physical energy that can be reliably detected by an observer (50% of the time)  Senses are sharp, but only tuned into narrow band of physical energies Difference Threshold  The smallest difference in stimulation that can reliably be detected by an observer when two stimuli are compared  Also called just noticeable difference (JND)  Weber’s law: size of JND proportional to size of initial stimulus  JND for weight is 1/30 Single detection theory  Divides the detection of sensory signals into a sensory process and a decision process  False alarm is type 1 error (false positive)  Miss is type 2 error (false negative) Sensory Adaptation & Deprivation Sensory adaptation  Reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious  Useful as it spares us from responding to unimportant information Sensory deprivation  The absence of normal levels of sensory stimulation  Varied responses somewhat dependant on expectations & interpretations (eg. hallucinations) Sensing Without Perceiving Selective attention  Focusing attention on selected aspects of the environment and blocking out the others Inattentional blindness  Failure to consciously perceive something you are looking at because you are not attending to it o Ie. You don’t notice the most obvious thing in front of you Vision: The Stimulus  Light = electromagnetic radiation o Amplitude: perception of brightness o Wavelength: perception of colour o Purity: mix of wavelengths o Saturation:  Light stimuli (waves) have physical characteristics that affect 3 psychological dimensions of our visual world 1. ADD  2. Brightness  Dimension of visual experience related to the amount of light emitted from or reflected by an object  Related to amplitude of wavelengths 3. Saturation  ADD An Eye on the World  Cornea: protects 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 dilates to let in more light Visual Receptors Retina  Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision  Rods: visual receptors that respond to dim light o Concentrated on the outside o Concentrated in the periphery of the retina o Highly sensitive to light (used for night vision) o Black & white  Cones: visual receptors involved in colour vision o Concentrated in the centre of the retina (foves) o Low sensitivity (used for day vision)  We experience chemical changes in rods & cones when our eyes adjust fully to dim illumination (called dark adaptation)  Retinal processing also involves ganglion cells o Neurons in the retina that gather information from receptors cells (by way of intermediary bipolar cells) o Axons form 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 & involves many types of cells in different brain regions o Cortical cells respond to lines of scientific orientations, others respond to properties of shapes & arrangements (eg. spirals, faces, greebies)  Feature 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  Figure: item of interest that stands out from the rest of the environment  Ground: environment background 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 ADD Depth and Distance Perception How We See Colour  Trichromatic theory o Proposes three basic types of cones, each sensitive to a certain range of wavelengths (red, blue, green) o Interaction of activity in three cones assumed to produce all the different exp
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