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Psychology 1000 (1,620)
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Chapter 5

Chap. 5,6,7,8 Nots

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Psychology 1000
Terry Biggs

1 Apologize reading try my best keep you guys entertained and awake Question about details to the end answer the question better with textbook Details will be available online or I can just email you 2 Read 3 Read 4 Signal Detection Theory Peoples apparent sensitivity can fluctuate quite a bit They concluded that the concept of a fixed absolute threshold is inaccurate because there is no single point on the intensity scale that separates uncertainty There is instead a range of uncertainty and people set their own decision criterion a standard of how certain they must be that a stimulus is present before they will say they select it Decision criterion can change depending on factors such as fatigue expectation and the potential significance of the stimulus Signal detection theory is concerned with factors that influence sensory judgementsSubliminal Perception A subliminal stimulus is one that is so weak or brief that although it is received by the senses it cannot be perceived consciouslythe stimulus is well below the absolute threshold James Vicary flashed subliminal messagesdrink Coke and eat popcorn on a theatre screen during a movie Results consumer behaviour cannot be controlled subliminally Subliminal stimuli had a greater affect on attitudes The Difference Threshold The difference threshold is defined as the smallest difference between two stimuli that people can perceive 50 of the time The difference threshold is sometimes called the just noticeable difference calculated by Webers Law TextbookSensory Adaptation Sensory systems are finely attuned to changes in stimulation Adaptation habituation is a part of everyday experience ie after a while leaky tap is unheard you smell horrible too lazy to shower 5 minutes later you are good adaptation occurs in all sensory modalities including vision if it werent for tiny involuntary eye movements that keep images moving about the retina stationary objects would simply fade from sight if we stared at them stabilize vision with contacts lensdisappearreappear Although sensory adaptation may reduce our overall sensitivity it is adaptive because it frees our senses from the mundane info and we are able to pick up informative changes in the environment 5 The Human Eye Light waves enter eye through the cornea a transparent protective structure at the front of the eye Behind the cornea is the pupil an adjustable opening that can dilate or contract to control the amount of light that enters the eye Low levels of illumination cause the pupil to dilate letting more light into the eye to improve optical clarity bright light triggers constriction of the pupil Behind the pupil is the lens an elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objects The lens reverses the image from right to left and top to bottom when it is projected upon the retina but the brain reconstructs the visual input into the image that we perceive The ability to see clearly depends on the lenss ability to focus the image directly onto the retina If you have a good vision for nearby objects but have difficulty seeing faraway objects you suffer from myopia nearsightednessyour lens focuses the visual images in front of the retina resulting in a blurred image for faraway objects Hyperopia farsightedness occurs when the lens does not thicken enough and the image is therefore focused on a point behind the retina too far from the lens 6 Photoreceptors The Rods and Cones There are about 120 million rods and 6 million cones in the human eye The rods which function best in dim light are primarily blackandwhite brightness receptors They are about 500 times more sensitive to light than are the cones but do not give rise to colour sensations The cones which are colour receptors function best in bright illumination In humans rods are found throughout the retina except in the fovea 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 and the periphery of the retina contains mainly rods Typically many rods are connected to the same bipolar cellfunnelless accurate This is why we can more easily detect a faint stimulus such as a dim star if we turn to make sure the image falls on the peripheral portion of the retina where the rods are packed more densely In the fovea however the densely packed cones each have their own private line to a single bipolar cell As a result our visual acuity of ability to see fine detail is greatest when the visual image projects directly onto the fovea The optic nerve formed by the axons of the ganglion cells exists through the back of the eye not far from the fovea producing a blind spot where there are no photoreceptors Brightness Vision and Dark Adaptation Rods are far more sensitive than cones under conditions of low illuminationStill the brightness sensitivity of both the rods and the cones depends in part on the wavelength of light Rods are not sensitive to red Dark adaptation is the progressive improvement in brightness sensitivity that occurs over time under conditions of low illumination After absorbing light a photoreceptor is depleted of its pigment molecules for a period of time During the process of dark adaptation the photo pigment molecules are regenerated and the receptors sensitivity increases greatly Pilots work under red light while waiting to be called for a mission Red light stimulates only the cones the rods remain in a state of dark adaptation ready for immediate service in the dark 7 Colour Vision The Trichromatic Theory This fact was the basis of an important trichromatic theory of colour vision advanced by Young and Hermann von Helmholtz
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