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Chapter 5

Chapter 5 summary

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Western University
Psychology 1000

Chapter 5 Sensation and Perception Chapter 5: Sensation and Perception - Synthesia is the experience of mixing sense o Experience sounds as colours or tastes as touch sensations have different shapes - Sensory-Impaired people provide glimpses into different aspects of how we sense and understand our world - Whether the stimulus is light, sound waves a chemical molecule, or pressure o Sensory receptors must translate information into the only language your nervous system understands Language of nerve impulses Process of transduction - Feature detectors o Specialized neurons that break down and analyze the specific features of the stimuli - Then numerous stimulus pieces are reconstructed into a neural representation that is then compared with previously stored information - This matching of a new stimulus with our internal storehouse of knowledge allows us to recognize the stimulus and give it meaning - Then we consciously experience a perception - We know what specific parts of the brain are specialized for different sensory functions o Some sort of cross wiring so that one activity in one part of the brain evokes responses in another part of the brain o Both normal perceptual processes and synaesthesia relate to one of the big mysteries in cognitive neuroscience Called the binding problem - The stimulation we receive through our sense organs in immediately organized and transformed into the experiences that we refer to as perceptions Sensation 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 is the active process of organizing this stimulus input and giving it meaning Sensory Processes - Brain cannot understand light waves, sound waves or the other forms of energy that make up the language of the environment - Contact with the outer world is possible only because certain neurons have developed into specialized sensory receptors o They transform these energy forms into the code language of nerve impulses - Many species have senses that humans lack together 1 Chapter 5 Sensation and Perception - Whatever the source of stimulation, its energy must be converted into nerve impulses o Only language the nervous system understands Transduction process whereby the characteristics of a stimulus are converted into nerve impulses - More than five classical senses with which were familiar with o Vision (sight) o Audition (hearing) o Touch o Gustation (taste) o Olfaction (smell) - There are senses that provide information about balance and body position - Sense of touch can be subdivided: o Pressure o Pain o Temperature - Immune system also has sensory functions that allow it to detect foreign invaders and to receive stimulation from the brain - We have specialized sensors that can detect many different kinds of stimuli with considerable sensitivity Psychophysics studies relations between the physical characteristics of stimuli and sensory capabilities o Concerned with two kinds of sensitivity Limits of sensitivity Differences between stimuli Stimulus Detection: Absolute Threshold Absolute Threshold lowest intensity at which a stimulus can be detected correctly 50% of the time - Lower the absolute threshold, greater the sensitivity Signal Detection Theory - A fixed absolute threshold is inaccurate o No single point on the intensity scale that separates non-detection from detection of a stimulus Decision Criterion: a standard of how certain they must be that a stimulus is present before they will say they detect it Signal Detection Theory: concerned with the factors that influence sensory judgements The Difference Threshold - The smallest difference between two stimuli that people can perceive 50% of the time o Also referred to as the just noticeable difference (jnd) - Webers Law 2 Chapter 5 Sensation and Perception o The difference threshold (jnd) is directly proportional to the magnitude of the stimulus with which the comparison is being made o Can be expressed as Weber fraction - Holds up reasonably well within the most frequently encountered range - The smaller the fraction, the greater the sensitivity to differences Sensory Adaptation - Sensory systems are finely attuned to changes in stimulation - Diminishing sensitivity to an unchanging stimulus is called sensory adaptation Adaptation: part of every day experience (sometimes called habitation) - Sensory adaptation may reduce our overall sensitivity o Its adaptive o Frees our senses from the constant and the mundane to pic up informative changes in the environment The Sensory Systems Vision - Normal stimulus for vision is electromagnetic energy, or light waves o Measure in nanometres - Our visual system is sensitive only to wavelengths extending from about 700 nanometers (red) down to about 400 nanometers (blue-violet) - ROY-G-BIV The Human Eye - Light waves enter the eye through the cornea o Transparent protective structure at the front of the eye - Behind the cornea is the pupil o Adjustable opening that can dilate or constrict to control the amount of light that enters the eye - Coloured iris that surrounds the pupil - Low levels of illumination cause the pupil to dilate o Bright light triggers constriction of the pupil - Behind the pupil is the lens o Elastic structure that becomes thinner to focus on distant objects and thicket to focus on nearby objects - The retina is light sensitive o Multi-layered tissue at the rear of the fluid-filled eyeball - Lens reverse the image from right to left and top to bottom when its projected on the retina o The brain reconstructs the visual input into the image that we perceive - Myopia is when the lens focuses the visual image in front of the retina resulting in a blurred image for faraway objects o Eyeball is longer than normal o Nearsightedness 3
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