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Sensation

Explore the fascinating world of sensation and perception, where our sensory receptors and nervous system receive and decode stimulus energy, allowing us to recognize meaningful objects and events. Discover how bottom-up and top-down processing play a role in our understanding of the world around us.

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Sensation

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  1. Sensation • Input from our physical world (raw information) • A process by which our sensory receptors and nervous system receive and decode stimulus energy

  2. Perception • a process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events • Raw information is constructed into our experiences • Sensation & Perception blend into one continuous process

  3. Sensation • Bottom-Up Processing • analysis that begins with the sense receptors and works up to the brain’s integration of sensory information • We process this way when we have no prior knowledge, start at the bottom and work our way up.

  4. Bottom-up Processing Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.”

  5. Top-Down Processing • information processing guided by higher-level mental processes • as when we construct perceptions drawing on our experience and expectations • Process this way when we have prior knowledge, start at the top and work to process the details

  6. Top-Down Processing THE CHT

  7. Top-Down Processing Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn’t mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

  8. Figure 4.26 Bottom-up versus top-down processing

  9. Making sense of the world Top-down processing: using models, ideas, and expectations to interpret sensory information What am I seeing? Bottom-up processing: taking sensory information and then assembling and integrating it Is that something I’ve seen before?

  10. Bottom-up vs. Top-down The Forest has Eyes – Bev Doolittle

  11. Selective Attention • The focusing of conscious awareness on a particular stimulus • We focus on a very limited aspect of what we experience and ignore the rest (like a flashlight beam)

  12. Cocktail Party Effect The ability to attend selectively to one voice among many UNTIL you hear your name or the name of someone close to you

  13. Selective Inattention • Inattentional blindness • Failing to see visible objects when our attention is directed elsewhere • We are “blind” to all but a tiny sliver of the immense array of visual stimuli constantly before us • Psychologists estimate our 5 senses take in 11,000,000 bits of information/second! • We CONCIOUSLY process about 40 bits • We UNCONCIOUSLY process remaining 10,999,960 bits

  14. Selective Inattention • Change blindness(a form of inattenional blindness) • Failing to notice changes in the environment • Magicians exploit our change blindness by riveting our attention on one hand’s dramatic act with inattention to the change accomplished by the other hand

  15. Change Blindness vs. Inattentional Blindness Change Blindness To detect a change requires a comparison of one image to be made to another one held in memory Inattentional Blindness The failure to detect an unexpected stimulus that is fully visible in a single display – It does not require a comparison to memory

  16. How do we study sensation? Psychophysics: A study of the relationship between physical characteristics of stimuli and our psychological experience with them.

  17. Absolute Threshold • The minimum stimulation necessary to detect a particular stimulus 50% of the time. • That 50-50 point of recognition, where you hear or sense it half the time, it defines your absolute threshold)

  18. Detection Absolute Threshold Intensity No No No Yes Yes Observer’s Response Detected Tell when you (the observer) detect the light.

  19. Absolute Sensory Thresholds • Vision: A single candle flame from 30 miles on a dark, clear night • Hearing:The tick of a watch from 20 feet in total quiet • Smell:1 drop of perfume in a 3-room apartment • Taste:1 teaspoon sugar in 2 gallons of water • Touch:The wing of a bee on your cheek, dropped from 1 cm

  20. Signal Detection Theory • Predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise) • assumes that there is no single absolute threshold • detection depends partly on person’s • experience • expectations • motivation • level of fatigue

  21. Subliminal Stimulation • Subliminal – below one’s absolute threshold for conscious awareness • Ex. Theaters flashing “eat popcorn” during a film • Subliminal stimulation assumes we can sense things below threshold • We can process information without being aware of it, but we are not always manipulated or persuaded by it.

  22. Priming The activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response. “Is this person happy or sad?” Most subjects will answer HAPPY!

  23. Difference Threshold Minimum difference between two stimuli required for detection 50% of the time, also called just noticeable difference (JND). Difference Threshold No Yes No Observer’s Response Tell when you (observer) detect a difference in the light.

  24. Difference Thresholds (JND) What is the minimum difference between two stimuli that a person can detect 50% of the time?

  25. Difference Thresholds (JND) (Ernst) Weber’s Law “Regardless of magnitude, two stimuli must differ by a constant proportion for the difference to be noticeable.”

  26. Weber’s Law Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Weber fraction: k = dI/I.

  27. Sensory Adaptation Diminished sensitivity as a consequence of constant stimulation. Put a band aid on your arm and after awhile you don’t sense it.

  28. Vision

  29. Vision • Transduction • Conversion of one form of energy to another • In sensation, transforming of stimulus energies into neural impulses • Physical characteristics of light – • Wavelength - The distance from the peak of one wave to the peak of the next (determines hueor color) • Intensity– The amount of energy in the light waves (influences brightness)

  30. Vision: Energy, Sensation, and Perception The Visible Spectrum We encounter waves of electromagnetic radiation. Our eyes respond to some of these waves. Our brain turns these energy wave sensations into colors.

  31. Great amplitude (bright colors, loud sounds) Short wavelength=high frequency (bluish colors, high-pitched sounds) Long wavelength=low frequency (reddish colors, low-pitched sounds) Small amplitude (dull colors, soft sounds) Vision - Physical Properties of Waves

  32. Wavelength (Hue) Violet Green Orange Red Indigo Blue Yellow 400 nm 700 nm Long wavelengths Short wavelengths Different wavelengths of light result in different colors.

  33. The Eye

  34. Parts of the eye Cornea: Transparent tissue where light enters the eye. Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light. Lens: Focuses the light rays on the retina. Retina: Contains sensory receptors that process visual information and sends it to the brain.

  35. The Lens Lens: Transparent structure behind the pupil that changes shape to focus images on the retina. Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.

  36. The Lens Nearsightedness: A condition in which nearby objects are seen more clearly than distant objects. Farsightedness:A condition in which faraway objects are seen more clearly than near objects.

  37. Retina The light-sensitive inner surface of the eye, containing receptor rods and cones in addition to layers of other neurons (bipolar, ganglion cells) that process visual information.

  38. Retina’s Reaction to Light- Receptors • Rods • peripheral retina • detect black, white and gray • twilight or low light • Cones • near center of retina • fine detail and color vision • daylight or well-lit conditions

  39. Receptors in the Human Eye Cones Rods Number 6 million 120 million Location in retina Center Periphery Sensitivity in dim light Low High Color sensitive? Yes No Vision- Receptors

  40. Bipolar & Ganglion Cells Bipolar cells receive messages from photoreceptors and transmit them to Ganglion cells, which converge to form the optic nerve. **in terms of order, think PBG…like a PBJ 

  41. Retina’s Reaction to Light • Optic nerve - nerve that carries neural impulses from the eye to the brain • Blind Spot - point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there • Fovea- central point in the retina, around which the eye’s cones cluster

  42. Visual Information Processing Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex. **in terms of order, think OTV…alphabetical order

  43. Pathways from the Eyes to the Visual Cortex

  44. How the Human Eye Sees • Light waves pass through the ______________( ), ____________ ( ) and )___________ • ( ). • The__________ (______________) controls the amount of light entering the eye by controlling the size of the pupil. • The ___________ changes shape (_______________) to focus the incoming light onto the ___________. • As the light strikes the _____________, the light energy activates the ________ and ________ (_______________), the central area where they ______and ________ cluster is the _________. • Signals from the_________ and _________ and collected by the ____________, which transmit the information to ____________. The ________________ axons are bundled together to form the ______________, which transmits information to the ______________ and then ___________in the brain. • The _____________ leaves the eye, creating a “___________” because no receptor cells are located there. cornea protects eye pupil lens adjustable opening transparent structure behind pupil iris colored muscle lens accommodates retina retina rods cones photoreceptors cones rods fovea cones rods ganglion cells bipolar cells ganglion cells optic nerve thalamus visual cortex optic nerve blind spot

  45. Visual Information Processing Feature Detectors • Specialized neurons in the visual cortex that react to the strength of visual stimuli, responding to shapes, angles, edges, lines and movement in our field of vision. • The brain takes all the info. it receives from the feature detectors and makes a series of interpretations that allow us to see what we see.

  46. Visual Information Processing Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses.

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