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Date Created: 02/28/16
Chapter 3: Sensation and Perception (lecture & textbook notes) Sensing and Perceiving the World: What is the difference between sensation and perception? • A sense is system that translates data from the outside the nervous system into neural activity. • A sensation is a detection of a physical stimulus such as light. • A perception the process through which people take raw sensations from the environment and give them meaning using knowledge, experience, and understanding of the world. o in other words: is the organization and interpretation of sensory input. o Ex: When you look out into a field and you see a cow, your brain can recognize that it is a cow from prior knowledge, experiences, and understanding the world. Sensory Systems: How does information from my eyes and ears get to my brain? • Intro: Your senses gather information about the world by detecting various forms of energy. Eyes detect light energy, ears detect the energy of sound, and skin detects energy of heat and pressure . All senses detect information about stimuli, encode it into neural activity, and then sends that encoded info to the brain. • The process: 3. Sensory 5. Cerebral Energy 1. Accessory 2. Receptor nerves 4. Thalamus cortex contains structure transduces transfer the processes and receives input informa▯on modiﬁes energy into coded ac▯vity relays the and produces aboou the engery. neural to the central neural the sena▯on world response. nervous repsonse. and system. percep▯on. (clip art here) • The 1st step: accessory structures which are structures that modifies an incoming stimulus. o Ex: the flexible outer part of your ear that extends to the outside of your head is an accessory structure that collects the sound. • The 2nd step: transduction, which is the process of converting incoming energy into neural activity o Ex: When your cell phone rings, its because your phone receives electromagnetic energy and tranduces it into sound. o Ex: The same way your ear receives sound energy and tranduces it into neural activity that you recognize as voices and music. • Transduction occurs the 3rd step of the process in a structure called neural receptors. These are cells that are specialized to detect certain types of energy and convert it into neural activity. These receptors respond to incoming energy by firing an action potential and releasing neurotransmitters that send signals to near by cells. • Sensory adaptation is the decreasing responsiveness to an unchanging stimulus. o Ex: Then you put on a wristwatch you eventually don’t realize it is still on. • Encoding translates the physical properties of a stimulus, such as its shape and intensity, into a pattern of neural activity that tells us what those physical properties are. o Your brain organizes these neural patterns, and make sense of the stimulus, and that is how you know you are looking at white car, a black shirt, or a tall person. Absolute Thresholds: Is Something Out There ? • Scientists discovered thresholds by exploring psychophysics, the relationship between physical energy in the environment and your psychological experience of that energy. • Absolute threshold is the smallest amount of energy that can be detected 50 percent of the time. • Noise is the spontaneous random firing of nerve cells that occur beca use the nervous system is always active. • Response Bias (Response Criteria) the internal rule a person uses to decide whether or not to report a stimulus. o This will depend on a person’s motivation (wants and needs) as well as expectations. • Signal Detection Theory is a mathematical model of what determines a person’s report of a near threshold stimulus. Judging Differences between Stimuli • When our bodies are detecting stimuli, sometimes it isn’t important to detect a faint stimulus. It is more important to notice small changes in a stimulus or to decide whether two stimuli are the same or different. o Ex: when you repair a wall, you have to judge whether or not the new paint matches the old wall color. o Ex: when you are cooking, you have to decide whether you soup tastes any spicier after adding spices. • It also depends on the strength of the stimuli. The smaller it is, the easier it is to detect differences. o Ex: If you have an orange in each hand, and one is bigger by even a fraction of an ounce, you will be able to tell that difference. However if you have two 50-pound boxes in each hand, you may not notice the difference. • Weber’s Law is a law that states that the smallest detectable difference in stimulus energy (just-noticeable difference) is a constant fraction of the intensity of the stimulus. Sensory Energy • Sensory energies of light an d sound vibrate as waves pass through space. This happens because of change in air pressure or reflected light. • Wavelength is the distance from one peak of the wave to the next. • Wave Frequency is the number of complete waves, or cycles, that pass a given point in a given amount of time. • Amplitude is the height of the wave from baseline to peak. Seeing: Why do some people need eyeglasses? Light • Light is a form of energy known as electromagnetic energy . This invisible to the human eye. o This includes: x-rays, radio waves, TV signals, Wi-Fi, and radar. • Light intensity is how much energy light contains which determines the brightness of light. • Depending on the Light wavelength is how you decide what color something is. o Ex: 440-nm light appears violet blue, and 700 -nm appears orangish-red. Focusing Light • Your eye transducers light energy into neural activity. • 1 : Light rays enter the eye by passing through the curved, transparent, pndtective layer called the cornea. • 2 : The light then passes through the pupil, the opening just behind the cornea. • 3 : The iris (give eye color) adjusts the amount of light allowed in the eye by constricting to reduce the size of the pupil or delighting it to enlarge it. • 4 : Behind the pupil is the l ens. o (both cornea and lens are curved to bend light . Ex: camera lens.) o this bending process focuses light rays coming from various angles into a sharp image on the inner surface at the back of eye. th • 5 : This surface is called the retina where the lens focuses light rays. • The Ocular Accommodation is the ability of the lens to change its shape and bend light rays so objects are in focus. Converting Light into Images • A conversion of light energy into neural activity takes place in the retina. • Special cells in the retina called photoreceptors convert light energy into neural activity. • There are two main types: Rods and Cones. o Rods are photoreceptors in the retina that allow sight even in dim light, BUT cannot distinguish colors. ▯ Located on the edge of the eyes o Cones are photoreceptors in the r etina that are less light sensitive than rods but that can distinguish colors. ▯ Located at the center of the eyes • This is related to why when you come inside after being out side in the sun it can be difficult to see. The chemicals in you rods and cones hav e to take a minute to adjust. • This is called dark adaptation, which is the increasing ability to see in the dark as time passes. • Cones are concentrated at the center of the eye in an area called fovea. The fovea is a region that focuses on light. o Cones are Specialized for daylight o Rods are specialized for night vision. Seeing Color (NOTE: these color concepts dealing with light are NOT the same as concept with mixing paint) • Hue is the essential color determined by the dominated wavelength of light. o Black, white, and grey are not considered hues because they don’t have a dominate wavelength. • Color Saturation is related to the purity of the color. o A color is more saturated or more pure if just 1 wavelength is more intense and contains more energy than another wavelength. o A yellow school bus or red stop sign are saturated color, but pastel colors are desaturated because whiteness is added to it. • Brightness is the overall intensity of the wavelength making up light. Theories of Color Vision : Trichromatic Theory & Opponent-Process Theory • Early 1800s, Thomas Young proved that if you mix pure version of blue, green, and red light in different ratios could produce any other color. Hermann von Helmholtz later confirmed the findings. The Young -Helmholtz theory of color vision is called Trichromatic Theory . o There are three types of cones (in the retina): ▯ Short-Wavelength is sen sitive to the blue range ▯ Medium-Wavelength is sensitive to the green range. ▯ Long-Wavelength is sensitive to the red ra nge. o Its saying that no single cone by itself can signal color in light. It is saying that a ratio of those three cones can signal a cert ain color ▯ Like a TV. • The trichromatic theory doesn’t explain after images. Therefore, Ewald Hering came up with the opponent-process theory. It states that the visual elements that are sensitive to color are grouped into red -green, blue-yellow, and black- white pairs. Hearing: How would my voice sound on the moon? ▯ Sound is a repeating fluctuation-a rising and falling-in the pressure of a substance, such as air. Sound ▯ Loudness is a psychological dimension of sound that is determined by the amplitude of a sound wave. o Measured in decibels (DB) ▯ Pitch is how high or low a tone sounds; pitch depends on the frequency of a sound wave. o The higher the frequency - the higher the pitch. (shorter) o Humans hear sounds between 20 -20,000 HZ ▯ Sounds that are a mixture of many frequencies and amplitudes creates sound’s timbre. o Quality of sound. The Ear ▯ Divided into three sections: ▯ External Ear o Pinna: the sound collecting cone. (The clumped part of the outer ear.) o Ear drum: is the membrane that vibrates as sounds waves hit it. ▯ Sounds conducted through vibrations of air. ▯ Middle Ear o Hammer, Anvil, Stirrup : 3 tiny bones. ▯ Sound conducted through movement of bones. ▯ Inner ear o Cochlea: it is a fluid filled coiled tunnel that contains the receptors for hearing ▯ Looks like a shell o The basilar membrane forms the floor of the fluid-filled duct that runs through the cochlea. ▯ As sound waves pass through the fluid in the tube, it makes the basilar membrane rise and fall. • This movement bends the hair cells on the membrane. They make connections with fibers from the acoustic nerve. They are a bundle of axons that go to the brain.
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