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Chapter 5

Chapter 5

31 Pages

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Michael Inzlicht

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Sensation, perception and attention - Sensation refers to how the sense organs respond to the external stimuli and transmit those responses to the brain - Perception refers to the processing, organization, and interpretation of sensory signals that result in an internal representation of the stimulus - Sensation is detection, whereas perception is construction - The bodily systems convert stimulus energy into useful information - Most of the time perception is based on past experiences, and this shapes our expectations during the identification of sensory experiences - The brain does not passively record information about the external world, rather, how we see and hear is a result of the brain processes that actively construct perceptual experiences to allow adaptation to an environment o This system can get details wrong, or fill in information that does not exist o But it does so in efficient and intelligent way so to produce a meaningful understanding of what is going on around us How do we sense our worlds? - Sensory organs gain information about the environment by converting forms of physical energy into signals that the brain can understand o This process has been shaped by evolution to Access potential dangers Identification of items - Because different species face different adaptive challenges, each species is sensitive to different types of physical energy o The information we sense and perceive has solved adaptive problems for humans over the course of the evolution 1. Stimuli must be coded to be understood by the brain - Sensory coding is the way sensory organs translate stimuli informations physical properties into neural impulses o Different features of the physical world are coded by different patterns of neural impulses www.notesolution.com Example: green light will be coded by one pattern, sensation of a hot skillet on your arm by another - Receptors are specialized neurons in the sense organs that pass impulses to connecting neurons when they receive chemical or electrical stimulation - Transduction is a process by which sensory receptors produce neural impulses when why receive physical or chemical stimulation o After transduction, the sensory neurons pass their information to the brain in form of neural impulses Most of the sensory information enters the thalamus and is then passed on to the cortex In the cortex, the incoming neural impulses are interpreted as sight, smell, sound, touch or taste o Sensation, then, refers to the transduced messages that are carried by the nerve impulses - Sensory coding can be divided into two categories, quantitative and qualitative o Quantitative factors such as intensity, brightness, and loudness Often indexed by the frequency of neural firing The higher the frequency the more intense is the stimulus The amount of neurons triggered also related to the quantitative category, more intense stimulus tends to recruit more neurons o Not useful for color and taste o Qualitative coding is possible because different sensory receptors respond to different qualities of stimulus Example: one class of receptors responds to red light and another to green But if this was the case for all the sensory systems, then we would need to have an enormous number of different receptors o And in most sensory systems, with exception of the olfaction, receptors provide a coarse coding, in which sensory qualities are only coded by a few www.notesolution.com receptors, each of which respond to wide range of different stimulus Only by comparing and integrating activity across the whole range of receptors do we compute the final percept 2. Psychophysics relates stimulus to response - Psychophysics examines our psychological experiences of physical stimuli o Asses such things as how much physical energy is required to detect that energy and how much change is required for us to notice a change in the stimuli a. Sensory threshold - Absolute threshold refers to the minimum intensity of stimulation that must occur before one can experience a sensation o Example: hearing threshold can be, how loud does a whisper have to be for you to be able to perceive it, or a quietest whisper you can hear - Difference threshold refers to the minimum amount of change required in order to detect a difference between the intensity of the stimuli o Just noticeable difference between two stimuli Difference threshold increases as the stimuli increases Example: easier to tell a difference between an one once object and a two ounce object than is it easier to tell the difference between a 5 pounds and 5pound and 1 ounce object o This principle is known as the Webers law and it states that the size of just noticeable difference is based on the relative proportion of difference rather than a fixed amount of difference Getting 6 our of 10 of getting 96 out of 100 b. Signal detection theory - Threshold is judged by human judgment - Concept of absolute threshold was flawed because sometime people perceived a stimulus when there wasnt one and sometimes missed one when there was one www.notesolution.com - Signal-detection theory states that detecting a stimulus requires making a judgment about its presence or absence, based on the subjective interpretation of ambiguous information o Example: radiologist and early signs of cancer Other information about the patient, like age, sex and family history will likely affect the judgment The consequences might also weigh over the radiologist, for example if its a false positive the patient will have to endure unnecessary procedures, but if its a false positive, she could miss a cancer - Signal- detection theory involves a series of trials in which a stimulus is presented on some trials and not during others o During these type of trials whether an even is present can have four outcomes Hit an event is present and detected Miss present, but missed False alarm not present but detected Correct rejection- not present and not detected Observers sensitivity to the stimulus is usually computed by comparing the hit rate with the false alarm rate o Response bias refers to a participants tendency to report detecting a stimulus on ambiguous trials Sometimes we need a lot of evidence before we can make a positive judgment, while during other we are willing to make a positive judgment easier Peoples expectations often influence the extent to which they are biased Example: solider whos expecting an immanent attack will err on the side of responding, perhaps having many false alarms www.notesolution.com
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