Sensation and Perception Modules 16-18

1. Sensation and Perception Modules 16-18

2. Basic Principles of Sensation • Sensation is the process that detects stimulation from our bodies and our environment.

3. Basic Principles of Sensation • Perception is the process that organizes those stimuli into meaningful objects and events and interprets them.

4. Basic Principles of Sensation Psychophysics is the study of how physical stimuli are translated into psychological experience.

5. Sensory Information Must Be Convertedinto Neural Impulses • Sound, light, etc. cannot travel through our nerves to the brain. • Sensory organs convert their physical properties into neural impulses. • This conversion process is called transduction.

6. Sensory Information Must Be Convertedinto Neural Impulses • Transduction takes place at sensory receptors. • Next, connecting neurons in the sense organs send this information to the brain. • The brain processes these neural impulses into what we experience. • Some stimuli are just as real as those that we can transduce, but they are not a part of our sensory experience.

7. Our Senses Vary in Their Sensitivity Thresholds • Absolute threshold: the lowest level of intensity of a given stimulus that a person can detect half the time • As people age, their absolute thresholds for all senses increase.

8. Our Senses Vary in Their Sensitivity Thresholds • Signal-detection theory contends that detection of a stimulus is influenced by observers’ expectations. • How likely is the stimulus to occur? • How important or rewarding is detecting it? • So absolute threshold may vary. • It is usually defined as the intensity of a stimulus that can be detected 50% of the time.

9. 100 Percentage of correct detections 75 50 Subliminal stimuli 25 0 Low Absolute threshold Medium Intensity of stimulus Sensation--Thresholds • When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”

10. Our Senses Vary in Their Sensitivity Thresholds • Difference threshold is the smallest difference between two stimuli that is detected half (50%) of the time. • It is also called the “just-noticeable difference” or jnd.

11. Our Sensory Receptors Adapt to Unchanging Stimuli • Sensory adaptation: the tendency for our sensory receptors to have decreasing responsiveness to stimuli that continue without change. • Auditory adaptation occurs much more slowly than adaptation to odors, tastes, and skin sensations.

12. Sensory Adaptation

13. We See Only a Narrow Band of Electromagnetic Radiation • Wavelengths of visible light range from 400 to 750 nanometers. • Shorter wavelengths are experienced as violet. • Intermediate ones as blue, green, and yellow. • Longer ones as red. • Other forms of electromagnetic energy that our eyes cannot detect are: • Radio • Infrared • Ultraviolet • X-ray radiation

14. Vision Spectrum of Electromagnetic Energy

15. 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) Physical Properties of Waves

16. Color and Wavelength of Light • An object appears as a particular color because it absorbs certain wavelengths of light and reflects others. • These wavelengths are simply energy; colors are created by our nervous system in response to them. • Species differ in what they see when looking at the same object. • Our difference threshold for colors is so low that the average person can discriminate about 2 million different colors.

17. Major Structures of the Human Eye

18. Retina’s Reaction to Light

19. Photoreceptors in the Retina Rods (125 million) Located at the edges of the retina. Are not involved in color vision. Function best under low-light conditions. Cones (7 million) Located near the center of the retina (the fovea). Require bright light to be activated. Play a key role in color vision.

20. 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

21. Pathways from the Eyes to the Visual Cortex

22. Cell’s responses Stimulus Visual Information Processing • Feature Detectors • nerve cells in the brain that respond to specific features of the stimulus • shape • angle • movement

23. Young-Helmholz Trichromatic Theory of Color Vision • Any color can be created by combining three primary colors—red, green, and blue. • The retina has three types of color receptors that produce the primary color sensations of red, green, and blue.

24. Additive and Subtractive Color Mixing

25. Opponent-Process Theory of Color Vision • Hering proposed a theory that color perception depends on receptors that make opposing responses to three pairs of colors: • black-white • red-green • blue-yellow

26. Afterimage

27. Color Constancy The relative constancy of perceived color under different conditions of illumination.

28. Color-Deficient Vision • People who suffer red-green blindness have trouble perceiving the number within the design

29. Sound Is the Stimulus for Hearing • Soundwaves (pressure) are created when an object vibrates. • Wave speed or frequency corresponds to pitch. • Amplitude (wave height) corresponds to loudness of a sound. • Most sounds are a combination of many different waves of different frequencies. • This sound complexity is caled timbre.

30. Auditory System: Three major parts of the Ear • Outer ear: • The pinna is the most visible part of the outer ear. • The auditory canal is funnel shaped. • The eardrum is at the end of the auditory canal and it vibrates in sequence with sound waves.

31. Audition- The Ear

32. Auditory System: Three major parts of the Ear • Middle ear: • The ossicles are three tiny interconnected bones—the hammer, anvil, and stirrup —that move and amplify sound waves before sending them to the inner ear.

33. Auditory System: Three major parts of the Ear • Inner Ear • innermost part of ear, containing the cochlea, semicircular canals and vestibular sacs • Cochlea • coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses

34. Sound Localization • Sound localization: the ability to locate objects in space solely on the basis of the sounds they make • Because the ears are only 6 inches apart, the time lag between the sound reaching both ears is very short. • Even such small time lags provide the auditory system with sufficient information to locate the sound.

35. Sound Localization

36. Pitch Perception: Place Theory • Place theory: contends that we hear different pitches because different sound waves trigger hair cells on different places of the cochlea’s basilar membrane.

37. Pitch Perception: Frequency Theory • Frequency theory: contends that pitch is determined by the frequency with which the basilar membrane vibrates.

38. Pitch Perception • Place theory best explains high-frequency sounds, while frequency theory best explains low-frequency sounds. Mid-frequency sounds are best explained by volley theory, a revision of frequency theory.

39. The Intensity of Some Common Sounds

40. Smell and Taste: The Chemical Senses • Olfaction: the sense of smell • The stimuli are airborne molecules • Olfactory receptor cells are at the top of the nasal cavity. • These cells transmit information to the olfactory bulb at the base of the brain. • The olfactory bulb processes this information and sends it to the primary olfactory cortex.

41. Smell

42. Olfaction • Olfactory sensitivity is determined by the number of receptors in the epithelium. • Odors can evoke memories and feelings associated with past events.

43. Smell and Taste: The Chemical Senses • Gustation: the sense of taste • Gustation occurs when a substance makes contact with special receptor cells in the mouth, called taste buds. • Most taste buds are located on the tongue, but some are in the throat and on the roof of the mouth.

44. Gustation: the sense of taste • When taste cells absorb chemicals dissolved in saliva, they trigger neural impulses, transmitted to one of two brain areas: • First: information first sent to the thalamus and then to the primary gustatory cortex, where taste identification occurs • Second: information sent to the limbic system, which allows a quick response to a taste prior to conscious identification of it (example, spitting out sour milk)

45. The Five Primary Tastes

46. The Skin Senses Pressure, Temperature, & Pain • Our skin is our largest sensory organ. • Sense of touch is actually a combination of three skin senses: • Pressure: physical pressure on the skin • Temperature: The skin contains two kinds of temperature receptors, one sensitive to warm and the other to cold.

47. Pain: The Body’s Warning System • Pain is induced through tissue damage or intense stimulation of sensory receptors. • Gate-control theory proposes that small-diameter nerve fibers (S-fibers) and large-diameter nerve fibers (L-fibers) open and close “gateways” for pain in the spinal cord. • Pain gateways can be closed—thus preventing pain messages from reaching the brain—by a class of substances known as endorphins.

48. The Proprioceptive Senses: Body Movement and Location • Kinesthetic sense: provides information about the movement and location of body parts with respect to one another • This information comes from proprioceptors (receptors in muscles, joints, and ligaments.) • Vestibular sense: provides information on the position of the body in space by sensing gravity and motion (inner ear).

49. Perception • Organization and interpretation of stimuli.

50. Perceptual Organization • Gestalt • an organized whole • tendency to integrate pieces of information into meaningful wholes