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Chapter 5

Chapter 5: Sensation

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PSYC 100

Amos Vivancos Leon 1 Chapter 5 sensation Sensation  Sensation: to detect physical energy from the environment and encode it as neural signals. The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.  Perception: to select, organize, and interpret our sensations. The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.  Bottom – up processing: analysis that begins with the senses and works up to the brain for processing. Start at the entry level through sensations.  Top-down processing: analysis that requires higher level mental process, constructing perceptions drawing both on sensations coming bottom-up to the brain and on our experience and expectations A. Threshold  Psychophysics: the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them. ➢ Absolute thresholds: the minimum stimulation needed to detect a particular stimulus 50 percent of the time. ➢ Signal Detection: detecting a weak stimulus or signal depends not only on the signal strength, but also on our psychological state. (experiences, expectations, motivations, alertness)  Signal detection theory: a theory predicting how and when we detect the presence of a faint stimulus (“signal”) amid background stimulation (“noise”). Assumes there is no signal absolute threshold and that detection depends partly on a person’s experience, expectations, motivation, and level of fatigue. ➢ Subliminal stimulation: Stimulation bellows one’s absolute threshold for conscious awareness.  Prime: the activation, often unconscious, of certain associations, thus predisposing one’s perceptions, memory, or response. ➢ Different thresholds: the minimum difference between two stimuli required for detection 50 percent of the time. We experience the difference threshold as a just noticeable difference. (AKA noticeable difference or JND)  Weber’s law: the principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount). E.g. For the average person to perceive their difference, two lights must differ in intensity by 8%, two objects in weight by 2% and two tones must differ in frequency by 0.3 %. A. Sensory adaptation: our diminishing sensitivity to an unchanging stimulus. Our sensory receptors are alert to novelty. Vision  Transduction: conversion of one form of energy into another. In sensation (sensory transduction), the transforming of stimulus energies, such as sight, sounds, and smells, into neural impulses our brains can interpret. E.g. we convert light energy into neural impulses. A. The stimulus input: light energy. -scientifically speaking, what strikes our eyes is not colour, but pulses of electromagnetic energy What we see as visible light is but a thin slice of what the whole spectrum of electromagnetic radiation. ➢ Two physical characteristics of light help determine our sensory experience are: 1. Wavelengths: the distance from one wave peak to the next which determines its hue (the colour we experience such as blue or green Amos Vivancos Leon 2  Hue: the dimension of colour that is determined by the wavelength of light; what we know as the colours. 1. Intensity: the amount of energy in light waves (determined by wave’s amplitude, or height) which influences brightness. A. The Eye:  Cornea: The areas were light enters, protects the eye and bends light to provide focus.  Pupil: after the cornea light passes through the pupil, a small adjustable opening in the center of the eye through which light enters.  Iris: a ring of muscle tissue that forms the coloured portion of the eye around the pupil and controls the size of the pupil opening.  Lens: the transparent structure behind the pupil that changes shape to help focus images on the retina. ○ Accommodation: the process by which the eye’s lens changes shape to focus near or far objects on the retina.  Retina: the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information.  Acuity: the sharpness of vision a) Normal Vision b) Nearsighted Vision c) farsighted vision Rays of light converge on the retina. The light rays from distant objects are The light rays from nearby objects This occurs for both nearby objects focused in from of the retina, when come into focus behind the retina, and, with appropriate readjustments in their images reach the retina; the rays resulting in blurred images the curvature of the lens, for objects are spreading out, blurring the image. far away. ➢ The retina: the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information  Rods: retina receptors that detect black, white, and grey; necessary for peripheral and twilight vision when cones don’t respond. To faint light.  Cones: retinal receptor cells that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. The cones detect fine detail and give rise to colour sensation. Light striking the rods and cones produces chemical changes that generate neural signals. These signals activate the neighbouring bipolar cells (help relay the cones individual messages to the visual cortex), which in turn activate the neighbouring ganglion cells. The axons from the network of ganglion cells converge like the strands of a rope to form an optic nerve.  Optic nerve: the nerve that carries neural impulses from the eye to the brain.  Blind spot: the point at which the optic nerve leaves the eye, creating a “blind” spot because no receptor cells are located.  Fovea: the retinas area of central focus. Cones cluster around the fovea-only contains cones. A. Visual Information Processing: ➢ Feature detection: nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement. Amos Vivancos Leon 3 Feature detection cells in the occipital lobe pass such information to other areas of the cortex where cells respond only to more complex patterns. E.g. one temporal lobe area allows face recognition, but not other objects, other areas respond to a face or arm movement in a particular direction. The brain activity that underlies perception combines sensory input with our assumptions and expectations. ➢ Parallel Processing: the processing of several aspects of a problem simultaneously; the brains natural mode of information processing for many functions, including vision. Doing several things at once. E.g. dividing a visual scene into sub-dimensions as colour, depth, movement, and form then works it aspect simultaneously. ➢ Colour Vision: White light is the combination of light waves of green, red, and blue.  Young-Helmholtz trichromatic theory: the retina contains three different colour receptor, one most sensitive to green, one to blue, and one to red. When stimulated in combination can produce the perception of any colour. People with color deficits lack functioning of one or more colors sensitive cones. (Genetically sex-linked defect)  Opponent Process theory: the theory that after leaving
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