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Department
Psychology
Course
PSY100H1
Professor
Dan Dolderman
Semester
Fall

Description
PSY100 SENSATION AND PERCEPTION CHAPTER 5 How do we sense our world? Way we experience world: Sensation: The sense organs’ responses to external stimuli and the transmission of these responses to the brain - eg. Light, air vibrations, odors etc Perception: The processing, organization, and interpretation of sensory signals; it results in an internal representation of the stimulus.  The essence of sensation is detection, the essence of perception is construction of useful and meaningful information about a particular environment  Perception is often based on our prior experiences, which shape our expectations about new sensory experiences  What we sense (see, hear, taste, touch or smell) is the result of brain processes that actively construct perceptual experiences and as a result, allow us to adapt to our environments’ details Stimuli Must be Coded to be Understood by the Brain  Sensory Coding: our sensory organs’ translations of stimuli’s physical properties into neural impulses  The brain cannot process raw stimuli, so the stimuli must be translated into chemical and electrical signals the brain can interpret Transduction: A process by which sensory receptors (specialized neurons in the sense organs) produce neural impulses when they receive physical or chemical stimulation  Connecting neurons then transmit information to the brain in the form of neural impulses  Most sensory information first goes to the thalamus, a structure in the middle of the brain  Neurons in the thalamus then send information to the cortex, where incoming neural impulses are interpreted as sight, smell, sound, touch, or taste  To function effectively, our brains need qualitative and quantitative information about a stimulus  Coarse Coding: sensory qualities are coded by only a few different types of receptors, each of which responds to a broad range of stimuli Psychophysics Relates Stimulus to Response Sensory Thresholds:  Absolute Threshold: the minimum intensity of stimulation that must occur before you experience a sensation, or the stimulus intensity detected above chance (eg. Absolute threshold for hearing is the faintest sound a person can detect)  Difference Threshold: the just noticeable difference between two stimuli- the minimum amount of change required for a person to detect a difference (eg. Minimum change in volume for you to detect a difference) o Weber’s Law: states that the just noticeable difference between two stimuli is based on a proportion of the original stimulus rather than on a fixed amount of difference) Signal Detection Theory: A theory of perception based on the idea that the detection of a faint stimulus requires a judgment- it is not an all-or-none process  Detecting a stimulus requires making a judgment about its presence of absence, based on a subjective interpretation of ambiguous information  Response Bias: refers to a participant’s tendency to report detecting the signal in an ambiguous trial o higher level processes in the brain, such as beliefs and expectancies, influence how sensations from the environment are perceived Sensory Adaptation  A decrease in sensitivity to a constant level of stimulation  Sensory systems tuned to detect environmental changes  If a stimulus is presented continuously, the responses of the sensory systems that detect it tend to diminish over time  When a continuous stimulus stops, the sensory systems respond strongly as well What are the basic sensory processes? In Taste, Taste Buds Detect Chemicals Gustation: The sense of taste  To keep poisons out of our digestive system while allowing food in Taste buds: Sensory receptors that transduce taste information - When food stimulates taste buds, they send signals to the brain, which then produces the experience of taste - Every taste experience is composed of a mixture of 5 basic qualities: sweet, sour, salty, bitter, and umami (“savory” or “yummy”) - The entire taste experience happens not only in the mouth, but also the brain, which integrates these various sensory signals - Supertasters: highly aware of flavours and textures and are more likely than others to feel pain when eating very spicy foods - Taste preferences come from our different numbers of taste receptors - Cultural influences also affect food preferences, and your mother’s preferences (passed on to offspring) In smell, the nasal cavity gathers odorants Olfaction: The sense of smell, which occurs when receptors in the nose respond to chemicals - Has the most direct route to the brain - We smell when chemical particles or odorants pass into the nose and when we sniff into the nasal cavity’s upper and back portions - In the nose and nasal cavity, odorants come into contact with: Olfactory Epithelium: The thin layer of tissue, within the nasal cavity, that is embedded with smell receptors - These receptors transmit information to the: Olfactory Bulb: The brain centre for smell, located below the frontal lobes - From here, smell information goes direct to other brain areas - Smell signals bypass the thalamus In touch, sensors in the skin detect pressure, temperature, and pain Haptic sense: the sense of touch - Conveys sensations of temperature, of pressure, and of pain and a sense of where our limbs are in space - Anything that makes contact with our skin provides tactile stimulation which gives rise to an integrated experience of touch - Haptic receptors for both temperature (separate hot and cold receptors) and pressure are sensory neurons that terminate in the skin’s outer layer - The integration of various signals and higher level mental processes produces haptic experiences Two types of pain - Warning system that stops you from continuing activities that may harm you - Actual experience of pain is created by the brain - Most pain experiences result when damage to the skin activates haptic receptors - Two kinds of nerve fibres identified with pain: o fast fibres for sharp, immediate pain o slow fibres for chronic, dull, steady pain - Important distinction between the fibres is the myelination or nonmyelination of their axons, which travel from the pain receptors to the spinal cord - Fast acting receptors activated by strong physical pressure and temperature extremes, slow acting receptors are activated by chemical changes in tissue when skin is damaged Gate control theory - Past experiences are extremely important in determining how much pain a person feels - Gate Control Theory of Pain: states that for us to experience pain, pain receptors must be activated and a neural “gate” in the spinal cord must allow the signals through to the brain o Pain signals transmitted by small-diameter nerve fibres, which can be blocked at the level of the spinal cord (prevented from reaching the brain), by firing of larger sensory nerve fibres - Sensory nerves fibres can “close a gate” and prevent or reduce the perception of pain - Worrying about or focusing on the painful stimulus, seem to open the pain gates wider - Division of perception of pain in the brain: o One area responds to the sensory input from the part of the body that is in pain- the full pain of a chronic backache, the stabbing pain of cut and so on o Other part of the brain that is involved when we feel pain registers the emotional aspects of pain, which includes how unpleasant it is - When we feel pain, both areas of the brain are activated In hearing, the ear detects sound waves Audition: The sense of sound perception - Second source of information to world (vision first) - Hearing results when the movements and vibrations of objects cause the displacement of air molecules - These molecules produce a change in air pressure, and that change travels through the air Sound Wave: the pattern of the changes in air pressure through time that results in the percept of a sound - The wave’s amplitude determines its loudness; higher amplitude is perceived as louder - The sensory experience of hearing occurs within the brain, as the brain integrates the different signals provide by various sound waves Eardrum (tympanic membrane): A thin membrane, which sound waves vibrate, that marks the beginning of the middle ear - Our ability to hear is based on the intricate interactions of various regions of the ear, which convert sound waves into brain activity, producing the sensation of meaningful sound - Changes in air pressure produce sound waves that arrive at the outer ear and travel down auditory canal to eardrum - Eardrum vibrations are transferred to ossicles (3 tiny bones called the hammer, anvil, and stirrup) - Ossicles transfer the eardrums vibrations to the oval window, a membrane of the cochlea, or inner ear (fluid filled tube that curs into snail like shape) - Pressure waves are created I the inner ears fluid and these waves prompt the hair cells to bend and cause neurons on the basilar membrane to fire - Hair cells are the primary auditory receptors - The mechanical signal of a sound wave hitting the eardrum is converted into a neural signal that travels to the brain via the auditory nerve Locating sounds - Sound reaches the ear that is closest to the sound first, the it reaches the second ear (indicating that the source is closer to the other ear) In vision, the eye detects light waves - Very little of what we see takes place in the eyes, rather what we see results from constructive processes that occur throughout much of the brain to produce our visual experiences Cornea: The clear outer covering of the eye (where light first passes through) - Focuses on incoming light in a process called refraction - Light rays then enter and are bent farther inward by the lens which focuses the light to for an image on the retina Retina: The thin inner surface of the back of the eyeball. The retina contains the photoreceptors that transduce light into neural signal Pupil: The small opening in the eye; it lets in light waves - Determines how much light enters the eye through either contracting or dilating Iris: The coloured muscular circle on the surface of the eye; it changes the shape to let in more or less light - The lens and cornea work together to collect and focus light rays reflected from an object, to form on the retina an upside-down image of the object Rods and Cones - The retina has two types of receptor cells; Rods: Retinal cells that respond to low levels of illumination and results in back- and-white perception (night vision) Photo pigments: light sensitive chemicals that initiate the transduction of light waves into electrical neural impulses Cones: Retinal cells that respond to higher levels of illumination and result in colour perception Fovea: The centre of the retina, where cones are densely packed Transmission from the eye to the brain - After light is transduced into neural impulses by rods and cones, other cells in the retina- bipolar, amacrine, and horizontal cells- perform on those impulses a series of computations that help the visual system process the incoming information - Ganglion cells: the first cells in the visual pathway to generate action potentials o send their signals along their axons from inside the eye to the thalamus o these axons gathered into a bundle, the optic nerve, which exits the eye at the back of the retina o blind spot: the point at which the optic nerve exits the retina has no rods or cones (in each eye) - ganglion cells lying within the visual areas of the thalamus are transmitted to the primary visual cortex The detection of visual information - Particular visual neurons respond best to particular colours, shape orientations, or directions of motion Receptive Field: The region of visual space to which neurons in the primary visual cortex are sensitive - Visual receptive fields can be thought of as being located on a specific region of the retina or a specific location in visual space Lateral inhibition Lateral Inhibition: A visual process in which adjacent photoreceptors tend to inhibit one another - Our visual systems are sensitive to edges because edges tell us where objects end The colour of light is determined by its wavelength - Not seeing colours, but seeing the light waves that objects reflect to our eyes - Visible light consist of electromagnetic waves and the colour of light is determined by the wavelengths of the electromagnetic waves that re
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