1. Sensation and Perception

2. What are Sensation and Perception?
Sensation is the information we receive from our five senses (sight, taste, touch, smell, and hearing)
The information goes to the CNS, where the brain interprets it
Perception is our interpretation of that information and how we react to it
We perceive information based on learning, past experiences, and attitudes

3. Absolute Thresholds
An absolute threshold is the weakest amount of a stimulus that can be sensed
Scientists have determined absolute thresholds for all five senses for the average person, but they vary by individual
Absolute thresholds for humans are different than those for animals (a dog’s hearing threshold is very different from ours

4. Difference Thresholds
A difference threshold is the minimum amount of difference we can detect between two stimuli
Think of hearing the notes of different keys on a piano
These differ from person to person as well

5. Signal Detection Theory
Many internal and external forces affect our ability to detect sensory information
SDT is the method of taking into account the strength of a stimulus but also environmental influences and an individual’s physical state and attitudes
It is much harder to detect the sound of someone’s voice in a quiet room than it is in a noisy one
The buzzing of fluorescent lights may be more distracting when you are stressed or have a headache
People tend to focus more on what they personally find important and ignore what they find unimportant

6. Sensory Adaptation
The process by which we become more sensitive to weak stimuli and less sensitive to unchanging stimuli
When you enter a very dark room, your eyes adapt to the new space and begin to detect weak sources of light
If you live in the city, your ears adapt to the constant sound of traffic in the background and detect other noise sources

7. Vision

8. Light Light is electromagnetic energy measured in wavelengths
Not all light is visible to humans
Visible light can be filtered into a variety of colors – each color has a different wavelength
Blue and violet have the shortest wavelengths, red has the longest

9. The Eye Works similar to a camera
Light enters the eye through the pupil
The lens adjusts to the distance of objects by changing its thickness
The image then is projected onto the retina – it acts like film in a camera
Neurons on the retina, called photoreceptors, react to the light and send the image to the occipital lobe of the brain

10. Rods, Cones, and the Blind Spot
Rods and cones are types photoreceptors that cover the retina
Rods – only sensitive to brightness of light, allow us to see in black and white
Cones detect colors within the light
The blind spot is the area of the eye that connects to the optic nerve – it does not have rods or cones and does not capture a light image at all

11. Color and Vision
People with normal vision can see any color in the visible light spectrum, but not all animals can
Cones in the eye are sensitive to certain colors – either blue, green, or red
When more than one type of cone is stimulated, we can perceive other colors like yellow, orange, and purple
TVs and computer screens use only blue, green, and red pixels to create color images

12. Color Blindness
People may be partially color blind if they cannot see all of the colors in the color spectrum
This occurs when cones malfunction or when people are born without a certain type of cone
Total color blindness occurs when people cannot see any colors, only black and white – this is a really rare condition

13. Hearing

14. Sound and Pitch
Sound is caused by vibrations that travel through the air in waves
How fast they complete a cycle determines their pitch
Shorter waves produce a higher pitch
Longer waves produce a lower pitch
A violin produces a higher pitch than a cello, which has longer strings and makes longer sound waves

15. Loudness
Loudness is measured by the height of sound waves – this is known as amplitude and is measured decibels
The absolute threshold of sound for humans (0 decibels) is the sound of a ticking watch 20 feet from the ear in a quiet room

16. The Ear
Shaped to capture sounds, vibrate with them, and transmit the sound to the brain
The eardrum is the thin membrane gateway between the outer and inner ear
As sound hits the eardrum, it vibrates and transmits the sound to three small bones
These bones vibrate the cochlea, a small bony tube filled with fluid and neurons that react to movement and send messages to the auditory nerve
The auditory nerve sends messages to the temporal lobe

17. Deafness
Conductive deafness – caused by damage to the middle ear, which amplifies sounds – can be treated with a hearing aid that amplifies noises
Sensorineural deafness – caused by damage to the inner ear or destruction of neurons in the cochlea, usually from prolonged exposure to loud noises – can be treated (sometimes) with cochlear implants

18. Smell, Taste, and Touch

19. Smell
Smell is linked with taste – when your ability to smell is impaired, your ability to taste decreases
Molecules in odors travel into the nose and contact receptor neurons high in the nose
These neurons send messages to the olfactory nerve
Our sense of smell is highly adaptable and we can quickly lose our awareness of certain smells

20. Our sense of taste is connected to smell, texture, and temperature
Apples and onions taste very similar, but their odors create very different flavors
We can distinguish four main taste qualities – sweet, sour, bitter, and salty
Receptor neurons on the tongue detect various qualities and send information to the brain
We regularly kill taste receptors, but they grow back within a week – the taste system is the most resilient of our senses
Taste

21. Skin Senses
Our skin can detect pain, pressure, and temperature – some receptors detect just one type of stimulus while others may detect all three
Many receptors are located at the roots of our body hair
They are not evenly distributed – parts of the body have many more receptors than others

22. Temperature and Pain Receptors
Temperature receptors are just below the skin, some detect warmth while others detect cold
Our sense of temperature is adaptable, we acclimate to warmer or cooler settings pretty quickly
Pain receptors motivate the body to try and stop the painful stimulus
Sometimes we can overload the brain’s messages to ease pain – rubbing an injury can distract the brain from pain signals

23. Body Senses
Vestibular Sense – our sense of balance – tells us when we are upright and whether we are falling or changing speed
Allows us to know that we are standing up or moving in an elevator when our eyes are closed
Kinesthesis – the sense that informs people about the position and motion of their bodies
Allows us to touch our nose with our eyes closed

24. Perception

25. How Do We Organize Sensory Information?
Our brain learns to use a variety of methods to sort and make sense out of sensory information
Closure
Figure-ground perception
Proximity
Similarity
Continuity
Common fate

26. Closure
The tendency to perceive or complete a whole figure even when there are gaps in what your senses tell you
You try to fit the pieces you have into a familiar pattern to create a whole image

27. Figure-Ground Perception
The perception of figures against a background
our perception can change depending on what we interpret as a background and what we view as a figure
We use this method of perception every day

28. Proximity Grouping objects because of its nearness to other objects
there is no reason to group the objects other than the fact it is located next to other objects

29. Similarity The process of grouping similar objects together
People often perceive of similar objects as being a part of the same group, even if they could be grouped differently

30. Continuity
People prefer to see smooth, continuous patters rather than disrupted ones

31. Common Fate
People or objects that move together or perform the same action must have the same purpose
A group of people running in the same direction must all be running to the same place – they have a common fate

32. Perception of Movement
We perceive movement when we see an object move in relation to other objects
We look for stable objects to use as markers for movement (buildings, trees, the sidewalk)

33. Stroboscopic Motion An illusion of movement
Created by showing a rapid series of images or objects that are not moving, but each image is just slightly different than the previous one (flip books)
Movies work in a similar way

34. Depth Perception People use two main cues to gauge distances
Monocular cues – need only one eye to be perceived
Perspective, clearness, overlapping, shadowing are used to determine which objects are closer and which are farther away
Binocular cues – need two eyes to be perceived
Retinal disparity – each retina captures different images of an object (finger test)
Convergence – our eyes try to maintain a single image of an object and turn inward, or converge, as the object gets closer

35. Constancies Everybody creates constancies in their minds
They are based on size, color, brightness and shape

36. Size Constancy
We perceive of an object to be one size no matter how far away it is and even though is creates a different-sized image on the retina
We base size constancy on past experiences
We know that a dog standing 20 feet away is the same size as if it was right next to us, even though our eye senses a smaller image

37. Color Constancy
We know that certain objects do not change colors even though we may not be able to see the colors
I know my house is the same color in the nighttime that it is during the day even though I cannot see its color without light

38. Brightness Constancy
We perceive of an object as being equally bright even when the intensity of light around it changes

39. Shape Constancy
We know that an object does not change shape even though it may look different from various angles
We know that a door is rectangular even though it may look like a trapezoid from some angles

40. Visual Illusions
Sometimes our constancies cause us to interpret information incorrectly
The visual cues we use fool our brains into perceiving objects as having a different size, shape, or color than they actually do