Unit 5 Sensation/Perception

Sensation v. Perception

• Sensation: activation of our senses (eyes, ears, etc.)

• Perception: the process of understanding sensations

Absolute Threshold

• the weakest amount of a stimulus required to produce a sensation

Difference Threshold

• The smallest change in a physical stimulus that can be detected between two stimuli.

• Weber’s Law - The larger or stronger a stimulus, the larger the change required for a person to notice that anything has happened to it.

http://www.youtube.com/watch?v=wVhiezByMSU

Sensory Adaptation

• Decreased responsiveness to stimuli due to constant stimulation.

OUR SENSES

Our Most Dominant Sense

The most studied sense

Parts of the Eye

Parts of the Eye

How the Eye Works

1. Light enters eye through pupil and reaches the lens.

2. The lens focuses the light on the retina.

3. Photoreceptors known as rods and cones turn the light energy into neuron impulses.

4. Neuron impulses travel along the optic nerve to the occipital lobe in the brain.

https://www.youtube.com/watch?v=o0DYP-u1rNM

Rods v. Cones

• Rods – Sensitive to low levels of

light – Basis of night vision – 75 to 150 million rods– See in black and white

• Cones – Require more light

before they begin to respond.

– Work best in daylight – 6 to 7 million cones – Sensitive to color

Color Deficiency

• Affects about 8% of American men and less than 1% American women

• It is a hereditary condition• Caused by cones not

functioning properly• Most people see some

colors• Very few people are totally

color-deficient

Other Common Eye Problems • Astigmatism - a person's cornea

is not evenly round, which causes light to focus at different distances inside the eye. When looking at an object, some parts may be in focus, while other parts are blurry.

• To correct this problem, the cornea must be reshaped to be more spherical, so as to correctly focus light on the retina.

• Nearsightedness is the inability to clearly distinguish objects at a distance. This happens when a person's eyeball shape is long, causing light to focus in front of the retina.

• To correct this, a person must either wear glasses or reshape the cornea to be flatter so that light travels through the lens and focuses correctly on the retina.

• Farsightedness is the inability to clearly distinguish objects up close. This happens when a person's eyeball shape is short (having too flat of a cornea), causing light to focus behind the retina.

• To correct this, a person must either wear glasses that cause the light to focus sooner or reshape the cornea to be more rounded so that light focuses correctly on the retina.

What happens if you cannot correct your vision and or you lose

you vision all together?

The Boy Who Sees Without Eyes

Hearing

Parts of the Ear

How the Ear Works1. Earflap (Pinna) directs sound waves down the auditory

canal. 2. Sound waves vibrate the eardrum. 3. Hammer, anvil, and stirrup vibrate and push against

cochlea.4. Pressure against the cochlea makes the liquid inside

move. 5. Tiny hairs inside the cochlea pick up the motion and

turn the sound vibrations into neuron impulses. 6. The auditory nerve carries the impulses to the cerebral

cortex. http://www.youtube.com/watch?v=fxZWtc0mYpQ

Deafness

• Conduction deafness– Bones of the middle ear

become rigid and cannot carry sounds inward

– Hearing aids can usually help

• Sensorineural deafness – Cochlea, hair cells, or

auditory nerve is damaged.

– Need a cochlear implant needed to correct deafness.

Smell

– When gaseous molecules come into contact with smell receptors in your nose allow you to smell.

– The message is then sent through the olfactory nerve to the brain.

Taste

Taste + Smell = Flavor • The sensation of flavor is actually a combination of taste and

smell.

http://www.youtube.com/watch?v=fxZWtc0mYpQ 3:33 to 4:29

Touch and Pain• http://www.youtube.com/

watch?v=mQoS62jEvNA• Receptors located in our skin

provide information about pressure, warmth, cold, and pain.

• Different nerve endings respond to pressure, temperature and pain

• Our brain interprets the amount of change and the place of the change

• Gate Control Theory of Pain – lessen some pains by shifting our attention away from the pain impulses

http://www.youtube.com/watch?v=ZfWO2wciIUY

Vestibular Sense

• Tells us where our body is oriented in space.• Our sense of balance.• Hair cells within the semicircular canals relay

information of our body orientation. When you turn your head, these canals also move. Inertia causes the fluid in the canals to resist changes in motion, which bends receptor hair cells projecting into the fluid.

• Over stimulation of the vestibular sense by movements such as spinning, falling, and tilting can cause dizziness and motion sickness.

Kinesthetic Sense

• Tells us where our body parts are.• Receptors located in our muscles and

joints send information to our brain about our limbs.

Perception

How we organize and interpret sensory information

I. Principles of Perceptual Organization

A. Proximity

When we see a number of similar objects, we tend to perceive them as groups or sets of those that are close to each other.

B. Continuity

We tend to see continuous patterns, not disrupted ones.

C. Similarity

When similar and dissimilar objects are mingled, we see the similar objects as groups.

D. Simplicity

We see the simplest shapes possible.

E. Closure

We fill in the gaps of missing information based on our previous experiences.

F. Figure-ground perception

• The ability to discriminate properly between a figure and its background.

• Also used for hearing. – Ex: When you are

following a person’s voice in a noisy room, that persons voice is the figure and the rest of the noise is the ground.

Perceptual Inference

• The phenomenon of filling in the gaps in what our senses tell us is known.

• Largely automatic and unconscious

Subliminal Perception

• Subliminal messages – brief auditory or visual messages presented below the absolute threshold so that there is less than a 50% chance that they will perceive it.

• 1974 subliminal advertising banned

• https://www.youtube.com/watch?v=OW9ou1kB1cU

Depth Perception

• The ability to recognize distances and three dimensionality

• Develops in infancy

http://www.youtube.com/watch?v=1VPaBcT1KdY&feature=player_embedded http://www.youtube.com/watch?

v=p6cqNhHrMJA

Monocular Depth Cues • Monocular Depth Cues

– Linear perspective (parallel lines appears to converge on a vanishing point)

– Relative height (more distant objects are higher)

– Relative size (more distant objects are smaller)

– Texture gradient- texture details, like roughness, diminish with distance

– Light and shadows –tell us about the shape and size. Brightly lit objects appear closer. While objects in shadows appear further away.

– Interposition – overlapping images lets us know which one is in front

Explain how the monocular depth cues are being used in this

painting.

Binocular Depth Cues

• Binocular depth cues – require two eyes– Retinal disparity – the greater the difference

between the images on your two retina, the closer the object

– Convergence – the greater your eye muscles must strain (or converge) to focus on an object, the closer the object (notice how hard your eyes strain when you focus on the tip of your nose).

Perceptual Constancythe tendency of animals and humans to see familiar objects as

having standard shape, size, color, or location regardless of changes in the angle of perspective, distance, or lighting.

Shape Constancy- perception that shape of an object doesn’t change just because image on the retina does.

Perceptual Constancy

• Size constancy – perception that an object’s size remain the same even as the retinal image changes.

Perceptual Constancy

Color Constancy – the perception that familiar objects have a consistent color, even if changing illuminations alter the wavelength reflected.

Illusions

• Incorrect perceptions as a result of perceptual cues being distorted so that our brains cannot correctly interpret space, size, and depth cues.