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Chapter 5

Psychology 1000- Chapter 5 Full Textbook Notes

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Psychology 1000

Chapter Five Sensation & Perception Sensation: the stimulus-detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain Perception: making sense of what our senses tell us the active process of organizing this stimulus input and giving it meaning Synesthesia: mixing of the senses Transduction: translating information into the language of nerve impulses Sensation stimulus received by sensory receptors receptors translate stimulus properties into nerve impulses (transduction) feature detectors analyze stimulus features stimulus features are reconstructed into neural representation neural representation is compared with previously stored information in brain matching process results in recognition and interpretation of stimuli Perception Sensory Processes Psychophysics: studies relations between the physical characteristics of stimuli and sensory capabilities. Concerned with two capabilities: 1. Absolute Limits of Sensitivity 2. Differences between Stimuli Absolute Threshold - lowest intensity at which a stimulus can be detected correctly 50% of the time - lower the AT, the greater the sensitivity Signal Detection Theory - concerned with the factors that influence sensory judgments - peoples apparent sensitivity can fluctuate Decision Criterion - a standard of how certain a person must be that a stimulus is present before they say they detect it - can change from time to time depending on fatigue, expectation, significance of stimuli Signal Detection Theory - concerned with the factors that influence sensory judgment - participants can be influence by manipulating rewards and costs for giving correct or incorrect responses - bold participants have more Yes and False Alarms than conservative patients who have the opposite Subliminal Stimuli - a stimuli so weak or brief that, although it is received by the senses, it cannot be perceived consciously the stimulus is below the absolute threshold - in terms of consumer behaviour, stimuli above the absolute threshold is far more influential EX. participants shown nine slides of a particular person attitudes measured for half the participants, each photograph was preceded by an unpleasant picture, the other half a pleasant picture unpleasant stimuli negative attitude pleasant stimuli positive attitude subliminal cues can bias what we perceive at a conscious level and may alter out conscious experience of those stimuli Difference Threshold - the smallest difference between two stimuli that people can perceive 50% of the time Webers Law - states that the difference threshold, or jnd, is directly proportional to the magnitude of the stimulus with which the comparison is being made - expressed as a Weber fraction EX. the Weber fraction for weights in 1/50 if you lift a weight of 50 grams, a comparison weight must weigh at least 51 grams in order for you to be able to judge as it as heavier - smaller the fraction, the greater the sensitivity to differences Sensory Adaptation - sensory systems are finely attuned to changes in stimulation - sensory neurons are engineered to respond to a constant stimulus by decreasing their activity - diminishing sensitivity to an unchanging stimulus is called sensory adaptation - adaptation (habituation) is an everyday experience that prevents your senses from feeling things (ie. a watch on your skin, cold water when you are swimming) - tiny involuntary eye movements keep images moving about the retina if these movements did not occur, stationary objects would fade from sight The Sensory Systems Vision The Eye Cornea: a transparent protective structure at the front of the eye where light enters Pupil: behind the cornea, an adjustable opening that can dilate of constrict to control the amount of light entering the eye Iris: coloured part, surrounds the pupil, muscles inside control the size of the pupil Lens: behind the pupil, an elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objects Retina: a multi-layered tissue at the rear of the fluid filled eyeball, visual images are focused here the lens reverses the image from right to left and top to bottom when it is projected upon the retina the brain reconstructs the visual input retina contains two types of light sensitive receptor cells (rods & cones) when the lens focuses on the visual image in front of the retina (too near to the lens), it results in myopia aka nearsightedness when the lens does not thicken enough and the image is therefore focused on a point behind the retina, it results in hyperopia aka farsightedness Photoreceptors - 120 million rods, 6 million cones Rods: function best in dim light, primarily black and white brightness receptors, 500 times more sensitive to light than cones Cones: colour receptors, function best in bright illuminationFovea: a small area in the centre of the retina that contains only cones - cones decrease in concentration as one moves away from the centre of the retina - the periphery of the retina contains mainly rods Cells Bipolar Cells: have synaptic connections with the rods & cones, they synapse with: Ganglion Cells: axons are collected into a bundle to form the optic nerve - many rods are connected to the same bipolar cell, therefore, they combine/funnel their individual electrical messages to the bipolar cell - this is why we can detect a faint stimulus - cones that lie in the periphery of the retina also share bipolar cells - they have a private line to a single bipolar cell - our visual acuity (ability to see fine detail) is greatest when the image projects directly on the fovea - the optic nerve formed by the axons of the ganglion cells exits through the back of the eye not far from the fovea, producing a blind spot Visual Transduction - the process whereby the characteristics of a stimulus are converted into nerve impulses - rods & cones translate light waves into nerve impulses through the action of protein molecules called photopigments - absorption of light by these molecules produces a chemical reaction that changes rate of neurotransmitter release at receptor synapse - the greater the change in transmitter release, the stronger the signal passed on to the bipolar cell and, in turn, to the ganglion cells whose axons form the optic nerve Brightness Vision and Dark Adaptation - brightness sensitivity of both rods and
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