1. Sensation and Perception

2. What is Sensation?  A “sensation” occurs when something around you changes…So what does that mean?  Any aspect of or change in the environment to which an organism responds is called a stimulus.  Example: a light switch being turned on fills a room with light.

3. What is Sensation?  A stimulus can be measured in a variety of ways including it’s size, duration, intensity, or wavelength.  A Sensation occurs anytime a stimulus activates one of your receptors.  The sense organs then detect any change in energy, such as light, heat, sound, and physical pressure.

4. What is a Perception?  A sensation may be combined with other sensations and your past experience to yield a perception.  A perception is the organization of sensory information into meaningful experiences.  What are the relationships between sensation and perception?

5. Psychophysics  Psychophysics: The study of the relationships between sensory experiences and the physical stimuli that cause them!  Ok, so that explains how sensation and perception are related…but how are they different?

6. Fraser’s Spiral  Fraser’s spiral illustrates the difference between sensation and perception. Our perception of this figure is that of a spiral, but it is actually an illusion. If you want, trace a circle carefully…You will always come back to the beginning!

7. Absolute Threshold  In order to determine how we judge sensation and perception, we must first figure out the weakest amount of a stimuli that is required to produce a sensation. In other words, we must find the absolute threshold.  The Absolute Threshold is: the level of stimulus that produces a positive response of detection 50% of the time!

9. The Absolute Thresholds for the “5” senses in humans are the following:  1. Vision: Seeing a candle flame 30 miles away on a clear night.  2. Hearing: Hearing a watch ticking 20 feet away.  3. Taste: Tasting 1 teaspoon of sugar dissolved into 2 gallons of water.  4. Smell: Smelling one drop of perfume in a 3 room house.  5. Touch: Feeling a bee’s wing falling a distance of one centimeter onto your cheek.

10. Sensory Differences and Ratios  Another type of threshold is the Difference Threshold.  The Difference Threshold refers to the minimum amount of difference a person can detect between 2 stimuli.  Example: A light dial is turned until you can see the light. That is the Absolute threshold. The light dial is then turned until you can say “yes, the light is brighter,” that is the difference threshold.

11. Weber’s Law  “The larger or stronger the stimulus, the larger the change required for a person to notice that anything has happened to it.”  Weber’s law: The principle that for any change in a stimulus to be detected, a constant proportion of that stimulus must be added or subtracted.

12. Reactions to Stimuli

13. Sensory Adaptation  Psychologists have found that your senses are the most responsive to increases and decreases, and to new events rather than to ongoing, unchanging stimulation.  We are able to respond to the changes in our environment because our senses have the ability to adapt, or adjust themselves, to a constant level of stimulation.  Once your senses get used to a new level of a stimulation, they respond only to deviations from it!

14. Examples of Adaptation  1. Your eyes eventually adjust to a darkened movie theatre. At first you see blackness, but eventually, you can see what is going on around you.  2. When you first jump into a pool that “feels cold” your body reacts to the stimulus. Eventually, your body adapts to the sensation and you become “comfortable.”  3. When you first walk into a sports locker room, the smell is almost nausiating. After a while, your senses adjust and you can hardly tell.

15. Adapting to the Darkness

16. What do you see…Or don’t you?

17. Signal Detection Theory  There is no sharp boundary between the stimuli you can perceive and the stimuli you cannot perceive.  The signal-detection theory studies the relations between motivation, sensitivity, and decision making in the presence of a stimulus.  Definition: The study of people’s tendencies to make correct judgments in detecting the presence of stimuli.

18. The Stroop Effect Try to name the colors as fast as you can. Not that hard right? How fast are you?

19. The Stroop Effect -Now, try to name the colors of the words you see here as fast as you can! -Not so easy is it? -How you like them apples? -Why was it more difficult to name these colors?

20. Vision!  Vision is the most studied of all of the senses!  How does vision occur?  1. Light enters through the pupil: The opening in the iris that regulates the amount of light entering the eye.  2. Light then reaches the lens: A flexible, elastic, transparent, structure in the eye that changes its shape to focus light on the retina.  3. Light then hits the retina: The innermost coating of the back of the eye, containing the light-sensitive receptor cells. Photo receptors = rods & cones.  4. This light energy is then turned into “neuronal impulses,” which are sent down the optic nerve: The nerve that carries impulses from the retina to the brain.

21. The Human Eye

22. Color Deficiency  When some or all of a person’s cones (light receptors) do not function properly, he or she is said to be color-deficient.  There are many different types of color deficiency. Most people see at least some form of color, but some see none.  Red – Green, Shades of gray, complete color loss.

23. Visual Definitions You Should Know…But We Will Not Go Into Detail On Them!  Binocular Fusion: The process of combining the images received from the two eyes into a single, fused image.  Retinal Disparity: The differences between the images stimulating each eye.  Pencil or pen test!

24. The “Changing Flag” Test  See Page 218 in your Textbook!  Read and follow the directions for figure 8.8!  What happened?

25. Hearing  Hearing depends on vibrations in the air called sound waves.  Sound waves from the air pass through various bones until they reach the inner ear, which contains tiny hair like cells that move back and forth.  These hair cells change sound vibrations into neuronal signals that travel through the auditory nerve to the brain.

26. Deafness  There are 2 types of deafness:  1. Conduction Deafness: occurs when anything hinders physical motion through the outer or middle ear or when the bones of the middle ear become rigid and cannot carry sounds inward. (Can be helped with a conventional hearing aid.)  2. Sensorineural Deafness: Occurs from damage to the Cochlea, the hair cells, or the auditory neurons. (Complete Sensorineural deafness cannot be helped by a hearing aid.)

27. Diagram of the Ear!

28. A few Definitions:  Auditory Nerve: The nerve that carries impulses from the inner ear to the brain, resulting in the perception of sound.  Vestibular System: Three semicircular canals that provide the sense of balance, located in the inner ear and connected to the brain by a nerve.  Olfactory nerve: The nerve that carries smell impulses from the nose to the brain.  Kinesthesis: The sense of movement and body position.

29. Perception

30. Perception  How do you perceive yourself? Those around you? Cars on the road? Noises? Buildings?  We do not merely have sensory experiences, we perceive objects! The brain recieves information from the senses and organizes and interprets it into meaningful experiences – unconsciously!  This process is called perception!

31. Perception  Through the process of perception, the brain is always trying to comprehend the confusion of stimuli that bombard the senses.  The brain makes sense of the world by creating whole structures out of bits and pieces of information in the environment!  This process is called Gestalt!  Gestalt: The experience that comes from organizing bits and pieces of information into meaningful wholes.

32. Figure-Ground Perception  The division of experience into figure and ground.  Figure-ground perception is the ability to discriminate properly between a figure and its background.  It is easy to distinguish between 3 dimensional objects, but what about 2 dimensional ones?

33. Let’s try this one!

34. Perceptual Inference  Often we have perceptions that are not based entirely on current sensory information.  For instance, when you hear barking as you approach your house, you assume its your dog – not a cat or a rhinoceros or even another dog!  When you are driving up a steep hill and cannot see the road over the hill, you assume that the road continues even though you cannot see it!  This Phenomenon is called Perceptual Inference: In other words, filling the gaps in what you actually know.

35. Subliminal Messages  Subliminal messages are brief auditory or visual messages that are presented below the absolute threshold.  They are presented below the “absolute threshold” so that there is less than a 50 percent chance they that they will be perceived.  Subliminal messages are not as common as you might think.  In fact, the vast majority of what you have probably heard is not true.

49. Depth Perception  In order to create a sense of “depth perception,” people use many monocular depth cues to perceive distance and depth.  Monocular depth cues are cues that can be used with a single eye.  One of these very important cues is called motion parallax.  Motion Parallax: the apparent movement of stationary objects relative to one another that occurs when the observed changes position!

50. A Little bit of Depth Perception

51. What is Constancy?  Constancy is the tendency to perceive certain objects in the same way regardless of changing angle, distance, or lighting.  For example, a friend walking towards you from a long distance away does not appear to turn into a “giant” regardless of the fact that the images in your eyes are becoming larger and larger as your friend approaches.

52. Illusions  What are illusions?  Illusions: perceptions that misrepresent physical stimuli.  Illusions can be very useful in teaching us how our sensation and perceptual rules work.  Illusions are created when our perceptual keys such as size, space, and depth cues are changed!

53. A very Strange Room!

54. Extrasensory Perception! Extrasensory Perception or “ESP”: An ability to gain information by some means other than the ordinary senses. There are 4 different types of “ESP”: 1.Clairvoyance – is perceiving objects or information without sensory input. 2.Telepathy – involves the reading of someone else’s mind or transferring one’s own thoughts. 3.Psychokinesis – involves moving objects through a purely mental effort. 4.Precognition – is the ability to foretell future events. ESP is a very highly contested topic! Why is this?

55. More Illusions!

58. Count the white and black dots!