1 Sensation and Perception Chapter 5

2 Sensation and Perception Basic Principles of Sensation and Perception  From Energy to Neural Impulse  Thresholds  Sensory Adaptation  Perceptual Set  Context Effects

3 Sensation and Perception Vision  Light Energy: From the Environment into the Brain  The Eye  Visual Information Processing  Visual Organization  Visual Interpretation

4 Sensation and Perception The Nonvisual Senses  Hearing  Touch  Pain  Taste  Smell  Body Position and Movement

5 Sensation and Perception How do construct our representations of the world? Sensation: the process by which our sensory receptors and nervous system take in stimuli from the environment Perception: The process by which our brain organizes and interprets that information and interprets that information as meaningful objects and events

6 From Energy to Neural Impulse The senses… –Receive sensory stimulation –Transform that stimulation into neural impulses (transduction) –Deliver the neural information to the brain Tranduction: the process of converting one form of energy into another; in this case, from photons and sound waves into neural signals.

7 Which stimuli do we sense? We are ignorant of many stimuli –X-rays, radio waves, ultraviolet and infrared light –Very high and very low frequency sounds

8 How much stimuli does it take to have a sensation? Absolute threshold: minimum stimulation needed to detect a particular stimulus 50% of the time

9 Detecting Stimuli, Finding Thresholds Audiologists can find the volume level you can detect 50% of the time for a given frequency.

10 Thresholds Difference threshold: the minimum difference between two stimuli required for detection 50% of the time –For example, parents needs to distinguish their own child’s voice from others Weber’s Law: to be perceived as different, two stimuli must differ by a constant minimum proportion (rather than a constant amount)

11 Weber’s Law By what proportion must different types of stimuli differ to be perceived as different? StimulusConstant Light (intensity) 8% Weight2% Tone (frequency) 0.3%

12 Sensory Adaptation Sensory adaptation: reduced sensitivity in response to constant stimulation –We eventually cease to notice a room’s bad smell after we’ve been there for a while

13 Perceptual Set The perceptual set is a mental predisposition to perceive one thing rather than another

14 Context Effects: Culture and Cues Box and tree? Window and column?

15 Vision  Light Energy: From the Environment Into the Brain  The Eye  Visual Information Processing  Visual Organization  Visual Interpretation

16 Visible Light

17 Light Energy: From the Environment into the Brain Light’s wavelength determines its hue, the color we experience. The amplitude, or height, determines the light’s intensity.

18 Visible Light Other organisms see different portions of the light spectrum. For example, bees cannot see red, but can see ultraviolet.

19 The Eye The retina, on the inner surface of the eye contains the photoreceptors (rods and cones) plus neurons that begin the processing of visual stimuli. Light is inverted by the lens, and is interpreted by the brain as upright vision

20 The Eye

21 Test Your Blind Spot There are no receptor cells where the optic nerve leaves the eye, creating a blind spot

22 The Retina: R ods and Cones Rods detect blacks, whites, and grays, and are necessary for peripheral and twilight vision Cones are clustered near the center of the retina, they detect fine detail and allow color vision

23 Differences Between Rods and Cones

24 Visual Information Processing How does the brain turn light stimuli into useful information about the world?

25 Visual Information Processing: The Crossover Information from the right visual field goes to the left hemisphere, information from the left visual and vice versa.

26 Feature Detection The visual cortex contains specialized feature detection cells, which respond to specific features –Such as edges, lines, and angles

27 Parallel Processing The brain uses parallel processing to assign different teams of cells to simultaneously process many aspects of scene or problem “

28 Visual Information Processing

29 Visual Organization How do we organize and interprets the shapes and colors into meaningful perceptions? People have the tendency to organize pieces of information into an organized whole, or gestalt.

30 Gestalt Principles Our brain does more than just register information about the world. We filter incoming information and we construct perceptions. Over the years, Gestalt psychologists have identified principles we use to organize our sensations into perception. –Form perception –Depth perception –Perceptual constancy

31 Form Perception How do we know where one object begins and another ends? –Figure-ground: organization of visual field into objects that stand out from their surroundings –Grouping: the perceptual tendency to organize stimuli into meaningful groups

32 Figure and Ground When seeing or hearing a scene, we identify figures, objects and events that stick out and hold our attention against the background. Example: following one conversation at a party. To the right: a scene with two options for seeing figures. Arrows? People?

33 Grouping: Seeing Gestalts/Wholes Our minds use these grouping strategies to see patterns and objects

34 Depth Perception Although the images that strike the retina are two dimensional, depth perception allows us to create mental images of objects in 3-D, and to judge distance

35 The Visual Cliff Eleanor Gibson and Richard Walk (1960) Test of early 3-D perception Most infants refuse to crawl across the visual cliff. Depth cue: Pattern on floor

36 Seeing Depth: Binocular Cues Binocular cues: Our two eyes help us perceive depth Retinal disparity: By comparing images from the two eyeballs, the brain can calculate the distance – the greater the disparity, the close the object –Used by 3-D film makers

37 Monocular Cues Retinal disparity can differentiate between 1 and 10 feet away, but not between 10 and 100 feet As such, we must rely on monocular cues, depth cues available to either eye alone

38 Monocular Cues Light and Shadow A AA rotated 180 degrees

39 Linear Perspective

40 Perceptual Constancy Things look different depending on the angle, distances, and lighting. How do we generate perceptual constancy, perceiving objects as unchanging?

41 Color constancy: we perceive familiar objects as having consistent color, even if changing illumination alters the reflected wavelengths Below is the same process, opposite effect: The color with the same wavelength is perceived as brighter in the shadows.

42 Shape and Size Constancy We perceive the shape of objects as constant while our retinas receive changing images We perceive the size of an object as constant from different distances However, context matters: consider the Moon illusion

43 Visual Interpretation Is our perceptual knowledge inborn? Or do we learn to perceive the world through our experiences?

44 Visual Interpretation Is our perceptual knowledge inborn? YES, to some extent. We come equipped to process sensory information Or do we learn to perceive the world through our experiences? YES, to some extent. For example, we learn to associate distance with size.

45 Experience and Visual Perception What does research reveal about the effects of experience on perception?

46 Sensory Deprivation and Restored Vision Some adults were born blind (clouded lenses from cataracts) then had surgery to remove cataracts –Patients could sense colors but, they could not visually recognize objects infant kittens and monkeys wore translucent goggles from birth –later they could not detect shape In both cases, the retinas still sent signals to the brain, but visual cortex had not developed its normal associations

47 Perceptual Adaptation We can adapt to an artificially displaced or inverted visual field George Stratton (1896) wore goggles that flipped images upside down and backwards

48 The Nonvisual Senses  Hearing (or audition)  Touch  Pain  Taste  Smell  Body Position and Movement

49 Hearing The Stimulus Input: Sound Waves Sound waves are compressing and expanding air molecules.

50 Sound Characteristics As with light waves, amplitude (height) determines intensity (loudness) Compression frequency: Low frequency = long wavelength = low pitch Sound is measured in decibels (dB) –0 dB is the absolute threshold (not the absence of sound, just less than we can hear) –60 dB is normal conversation –85+ dB: prolonger exposure can cause hearing loss

51 Decoding Sound Waves 1.Sound waves strike the ear drum, causing it to vibrate 2.Tiny bones in the middle ear pick up the vibrations and transmit them to the cochlea, a coiled, fluid-filled tube in the inner ear 3.Ripples in the fluid of the cochlea bend the hair cells lining the surface, which trigger impulses in nerve cells 4.Axons from these nerve cells transmit a signal to the auditory cortex

52 The Ear is Sensitive! A neural response is triggered when the tiny bundles of cilia on top of even one of the 16,000 hair cells on the cochlea are moved even the width of an atom!

53 How Do We Locate Sounds? The placement of our two ears helps us in two ways. Sounds to the closer ear… 1. Are more intense 2. Arrive sooner That’s why it’s hard to tell if a sound is directly behind or in front of you

54 Touch Our “sense of touch” is actually a mix of four distinct skin senses: –Pressure –Warmth –Cold –Pain

55 Pain Pain is your body’s way of saying “something has gone wrong” No one type of stimulus produces pain. At low intensities, the same stimulus that produces pain can cause other sensations, such as warmth or coolness, roughness or smoothness.

56 Controlling Pain Pain is where body meets mind Built-in controls: endorphins + distraction Virtual reality distraction helps a burn victim feel less pain (below) Pain is a combination of body and mind

57 Hypnosis and Pain Relief Hypnosis: a social interaction in which one person suggests to another that certain thoughts, feelings, perceptions, or behaviors will spontaneously occur –Useful for relieving pain

58 Taste Traditionally, taste sensations consisted of sweet, salty, sour, and bitter tastes. Some have claimed that there is a fifth taste called umami. B ut most sensory psychologists say-- nay

59 Tastes Exist for a Purpose [Insert table 5.2]

60 Taste Is A Chemical Sense Inside each little bump on the top and sides of the tongue are 200+ taste buds Each bud contains a pore with taste receptors, each of which react to different types of food molecules and send messages to the brain

61 Taste is Psychological Perceptual bias can influence taste –People thought a $10 bottle of wine tasted better when told it cost $90 Sensory interaction: one sense may influence another Smell + texture + taste = flavor

62 Other Examples of Sensory Interaction A person with hearing loss can “hear” a video when subtitles are include People are more likely to rate someone as “warm” and treat them more generously after holding a warm vs. a cold drink Seeing a face forming words helps someone hard of hearing to understand spoken words

63 Smell Like taste, smell is a chemical sense –Smell occurs when molecules in the air reach the cluster of 5 million olfactory receptor cells at the top of each nasal cavity There are hundreds of different receptors –Different combinations of receptors identify different smells Odors can evoke strong memories

64 Taste, Smell, and Memory

65 Body Position and Movement Kinesthesis: The system for sensing the position and movement of individual body parts –Interacts with vision Vestibular sense: the sense of body movement and position, including the sense of balance

66 Where Sensory Information Goes Sensory nerves carry sensory information to the brain. where it is processed to form perceptions.