Sensation and Perception Chapter 4

The Basics Sensation – Involves the stimulation of sensory receptors and the transmission of sensory information to the central nervous system »i.e. spinal cord and brain Things that tip off sensory receptors: Light, sound, smells, etc.

The Basics Perception – How we interpret sensory stimulation Football field example –Perception reflects learning, expectations and attitudes

Absolute Threshold The weakest amount of a stimulus that can be tested Dogs v. Humans –Thresholds are different amongst people –More sensitive than others

Some established absolute thresholds are: vision: a candle flame 30 miles away on a clear night. hearing: a watch ticking 20 feet away taste: 1 teaspoon of sugar dissoved in 2 gallons of water smell: a single drop of perfume in a three-room house touch: a bee's wing falling a distance of 1 centimeter onto the cheek.

Difference Threshold The minimum amount of difference detected between two stimuli Tone Hue Piles of sand

Signal-Detection Theory Distinguishing sensory stimuli that takes into account all factors of self and environment We focus on what we consider important

Sensory Adaptation Process by which we become more sensitive to weak stimuli and less sensitive to unchanging stimuli –Eyes adapting to darkness –Waves on a beach –Traffic

Section 2 - Vision Color spectrum – Roy G. Biv

The Eye Similar to a camera Light enters the eyes, and then is projected onto a surface –The amount of light that enters is determined by the opening in the colored part of the eye »The pupil

The Eye Once light enters, it meets the lens –The lens adjusts to distances of objects by changing its thickness »Finger test – near / far

The Eye The changes in thickness and light project a clear image onto the retina –The retina acts like the film of a camera –Neurons in your retina that are sensitive to light are called photoreceptors –Once the photoreceptors are activated a nerve carries the information to the brain – occipital lobe

The Blind Spot We need the blind spot to see A point left empty of photoreceptors – room for information to travel –Circle test

Rods and Cones 2 kinds of photoreceptors –Rods – sensitive only to the brightness of light –Cones – provide color

Dark and Light Adaptation Your ability to see in low light improves for 45 minutes Sundown Adaptation to light happens much more quickly

Visual Acuity Vision tests for sharpness –20/20 As you age your lenses become brittle, and you may become farsighted Holding reading material further away

Color Vision Human beings can see up to 1 million different hues Animals are more sensitive to certain colors The color circle Afterimages Color blind – distinguishing colors from each other Total color blindness is extremely rare

Section 3 Hearing – a series of vibrations in the form of sound waves in its own unique pitch or loudness –Hearing experiment

Pitch The more cycles (sound waves) per second, the higher the pitch (high or low) –Women’s voices are at a higher pitch than men’s because their vocal cords tend to be shorter –Humans – 20 to 20,000 per second –Dogs / Dolphins / other animals in excess of 20,000

Loudness Measured in dB (decibels) –Loudness is determined by the height / amplitude of sound waves »0 decibels is the threshold (a watch heard ticking at 20 feet away)

Locating Sound Perception of sound Infinite possibilities –How your body / senses react to sound

Deafness Inherited / Disease / Injury / Old Age Conductive Deafness – –Damage to middle ear, sound is not amplified Helped with hearing aides Sensorineural Deafness –Damage or elimination of neurons, damage to auditory nerve Cannot be helped if nerve itself is damaged Cochlear implants can help neuron loss

Section 4 Other Senses – –Smell – incredibly important, apples and onions would be relatively the same otherwise –Taste – Spheres of the tongue Smell and taste work together when eating

Skin Senses Touch Infants grow quickly and stay healthier if touched –Older people do better if they have pets (cats / dogs) Body is covered in hairs, many too small to see –Sensory receptors lie at the base of the hair Do we actually “touch”?

Temperature Differences are all relative –Fevers –Outside heat (Summer) –Swimming pools –A/C

Pain The more pain receptors are located in a certain body, they more we will feel Point of contact > Spine > Thalamus > Brain (processing) –Prostaglandins help transmit messages »Ibuprofen and aspirin help slow prostaglandins

Pain Why does rubbing or scratching painful areas help? Mixed signals Phantom limb pain

Body Senses Vestibular Sense –Sensory organs in your ears monitor your motion and relation to gravity –Balance, standing, changing speeds, etc. Kinesthesis –Position and motion of your body –Copying body motions

Section 5 Perception – the way our body makes sense of our sensory impressions Gestalt psychology – “The whole is more than the sum of its parts”

Rules of Perceptual Organization Closure – filling in the gaps to get a complete picture –Fig 4.11 (p. 93) »Filling in the blanks because dogs are familiar to you

Rules of Perceptual Organization Figure-Ground Perception –What do we perceive as the figure and what do we perceive as the background »Fig 4.12 (Vases or Faces)

Rules of Perceptual Organization Other Rules - –Laws of: Proximity Similarity Continuity Common Fate

Rules of Perceptual Organization Perception of Movement –To sense movement we need a change of position –Your senses need clues to tell you that you are moving –Trees, road bumps, etc.

Rules of Perceptual Organization Stroboscopic Motion –The illusion of movement Flipbooks Movies on reels –Subliminal messages –Perception smoothes out the gaps –Humans prefer smooth images

Rules of Perceptual Organization Depth Perception –The “distance away” –Monocular clues – the appearance of 3-D on 2-D surfaces –i.e. paintings »Clearness, shadow, texture, overlapping, perspective –This is done through stimulation of retina

Monocular Cues Clearness – faraway objects seem less detailed Perspective – parallel lines coming together or moving apart Overlapping – placing of one object in front of another Shadows and highlights – give a 3-D feel Texture Gradient – closer objects have more texture (gradient – progressive change) Motion parallax – the tendency of objects to seemingly move forward or backward depending on distance away Moon, stars v. trees and rocks while driving

Binocular Cues Need both eyes v. one eye for monocular –2 cues in binocular: Retinal Disparity Convergence

Binocular Cues Retinal Disparity – only works on objects that are very close –Difference of angles of an object as seen by both retinas Convergence – associated with a tightness of the eye muscles on things up close –Magic Eye puzzles

Perceptual Constancies Size Constancy – Comes through experience –Perceiving an object as one size no matter the distance –Pygmy example p. 98

Perceptual Constancies Color Constancy –The tendency for objects to maintain color no matter the light quality Brightness Constancy –Tendency to find an object equally bright even when its surroundings change

Perceptual Constancies Shape Constancy –The knowledge an item has one shape »i.e. top of a glass from different angles

Visual Illusions When the rules of constancies are violated