Chapter 5: Sensation & Perception
Chapter 5: Sensation & Perception PSY 201
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This 6 page Class Notes was uploaded by Rachel Kasashima on Friday November 6, 2015. The Class Notes belongs to PSY 201 at University of Oregon taught by Dassonville P in Fall 2015. Since its upload, it has received 83 views. For similar materials see Mind and Brain >3 in Psychlogy at University of Oregon.
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Date Created: 11/06/15
CHAPTER 5: SENSATION & PERCEPTION • Sensation: initial coding of information from the senses ex. Loud noise, yellow blur, fast motion, wind in face, exhaust smell Gathering of information from the environment (sensory stimuli) • Perception: brain's interpretation of those messages ex. Taxi blaring its horn as it narrowly misses you (representation of what happened) Transformation into a virtual world in the mind (mental representation) • The Senses What senses do we have? ‣ Vision (sight) ‣ Audition (hearing) ‣ Somatosensation (touch) ‣ Olfaction (smell) ‣ Gustation ("taste") ‣ Kinesthesis (moving body awareness); proprioception (still body awareness) ‣ Vestibular sense (balance) What is it that we sense? ‣ Light waves (sight) ‣ Vibrations in the air (hearing) ‣ Deformation/temperature/pain of skin (touch) ‣ Chemicals in the air we breathe (smell) ‣ Chemicals in the food we eat ("taste") ‣ Muscle stretch & joint angles (kinesthesis; body awareness) ‣ Gravity & motion (balance) Somatosensation ‣ Sensory transduction: Process of converting energy (information) in the environment into energy (information) in the nervous system; accomplished by specialized neurons (sensory receptors) ‣ Sensory coding: Translation of physical properties of stimulus into patterns of neural activity (action potentials) • Doctrine of speciﬁc nerve energies Sensory Thresholds ‣ Psychometric function ‣ Absolute Threshold: Smallest amount of energy needed to detect a stimulus ‣ Difference Threshold: Smallest detectable difference (the just noticeable difference, jnd) between two stimuli ‣ Weber's Law: The jnd is proportional to the magnitude of the original stimulus (ex. larger stimulus leads to larger jnd) "Taste" = gustation + olfaction + vision + mouth feel Doctrine of speciﬁc nerve energies vs. rate law Vision ‣ The Retina • Photoreceptors are sensitive to light The Photoreceptors: Rods and Cones ‣ Photopigment (Rhodopsin) ‣ Opsin + retinal ‣ Rods • 120 million (more rods than cones) • Has a high sensitivity to dim light • No sensitivity to color • Low sensitivity to ﬁne detail • Primarily located in periphery ‣ Cones • 6 million • Low sensitivity to dim light • Sensitivity to color • High sensitivity to ﬁnd detail • Primary location in the fovea Fovea: Area in the center of the retina with high density of cones, and overlying cell layers pulled aside, to provide high- resolution images of the central part of the visual scene Blind spot: Area of retina in which the ganglion cell axons depart the eye along the optic nerve, crowding out any photoreceptors. ‣ Light (The Electromagnetic Spectrum) • Gamma rays, X rays, Ultra-violet rays, [VISUAL SPECTRUM (white light)], Infra-red rays, Radar, TV/FM radio, Short wave, AM radio, AC circuits • Color does not exist in the physical world. It only exists in our mind • Color Dimensions Hue=wavelength ‣ Longer wavelength=violet, shorter wavelength=red Brightness=amplitude Saturation=purity ‣ Trichromatic Theory of Color Vision • Three cone types that are sensitive to different parts of the spectrum Perception of color is dependent on the relative activations of the three types of cones. • Additive colors Red+Green=Yellow; Green+Blue=Cyan; Blue+Red=Magenta; All colors mixed together=white • Subtractive Colors Magenta+Yellow=Red; Yellow+Cyan=Green; Cyan +Magenta=Blue; All colors mixed together=black ‣ Opponent Process Theory of Color Vision • Retinal ganglion cells are either: excited by green/ inhibited by red excited by red/ inhibited by green excited by blue/ inhibited by yellow excited by yellow/ inhibited by blue excited by white/inhibited by black excited by black/inhibited by white • Opponent colors: red & green blue & yellow black & white • Bottom-up vs. Top-down Processing Bottom-up processing: Hierarchical sensory processing that relies only on information available in the sensory input Top-down processing: Hierarchical sensory processing that relies on prior knowledge of the properties of the objects o r events to be detected Sometimes, the brain's assumptions of how the world works can be misleading. Reversible Images (Ambiguous Figures) • Depth Cues Pictorial cues are those that can be depicted in a still picture Pictorial (Monocular) Depth Cues ‣ Occlusion (Interposition): If one object partially hides another from view, the object that is blocked is seeing as being further away. • Only provides information on relative (not absolute) depth ‣ Relative Height: Objects that are closer to the horizon in the visual ﬁeld appear further away ‣ Cast Shadows: If source of light is known, the location of a shadow can provide further information of an object's location in depth ‣ 3-D Shape from Shading: Highlights and shadows are cast on an object in a way that is consistent with... • the object's shape in depth, and • the known (or assumed) sources of light ‣ Relative Size: If two objects are the same size, the one whose image takes up less of the visual ﬁeld (smaller) will appear to be further away. ‣ Familiar Size: If the actual size of an object is known, its distance can be judged by the size of its visual image--a more distant object will have a smaller image. ‣ Atmospheric (Aerial) Perspective: Distant objects look less sharp than nearby objects due to the greater amount of dust, water vapor, and pollution we have to look through to see the more distant object ‣ Linear perspective: Lines that are actually parallel will converge in the image as distance increases ‣ Texture gradient: Elements that are equally spaced will appear to be packed closer and closer together as distance increases Oculomotor cues are based on our ability to sense the position of our eyes and the tension in our eye muscles ‣ convergence: eyes must "converge" to see nearby objects ‣ accommodation: lens changes shape to focus the image Movement-produced cues are created by movement of the observer or by movement of the objects in the environment ‣ Motion parallax: Nearby objects move across the visual image faster than more distant ones ‣ Structure from Motion: you can see a structure based on movement of parts Binocular disparity uses the fact that our left and right eyes receive slightly different images because they are observing the scene from slightly different positions ‣ Disparity: the difference in the images of the two eyes, caused by the eyes' slightly different locations in space ‣ Stereopsis: the impression of depth that is derived from disparity • Color Blindness: Ishihara Plates Types of Color Vision ‣ Trichromatopia: typical color vision, with three functional cones ‣ Dichromatopia: Atypical color vision, caused by a genetic mutation that prevents the formation of one cone type • Protanopia: defective L-cones (red end of the spectrum); ~1% of men, .02% of women) • Deuteranopia: defective M-cones; ~1% of men, .02% of women • Tritanopia: defective S-cones; ~.001% of men, .03% of women ‣ Monochromatopia: Atypical color vision, caused by a genetic mutation that prevents formation of two or three of the cone types; ~.00001% of men and women • Although you might have one functional cone, you have nothing to compare it to ‣ Anomalous color vision: Atypical color vision, caused by a genetic mutation that alters (but does not eliminate) the function of one or more cone types; ~6% of men, .4% of women ‣ Tetrachromatopia: Atypical color vision, caused by a genetic mutation that effectively causes a fourth cone type to develop (thought to occur in ~1% of women; see 100x more colors than typical) ‣ What the world would look like:
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