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Sensation & Perception

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1 Sensation & Perception
Chapter 4: Sensation & Perception “All knowledge has its origins in our perceptions.” – Leonardo Da Vinci Vision Hearing Smell Taste Touch

2 Sense organs: eyes, ears, nose, tongue, skin, & internal body organs
Definitions Sensation process of detecting, converting, and transmitting raw sensory information from the external and internal environments to the brain Perception process of selecting, organizing and interpreting sensory information enables us to recognize meaningful objects and events Sense organs: eyes, ears, nose, tongue, skin, & internal body organs Happens in the brain!

3 Sensation Bottom-Up Processing Top-Down Processing
Information processing beginning “at the bottom” with raw sensory data that are sent “up” to the brain for higher level analysis Data driven processing that moves from the parts to the whole Top-Down Processing Information processing starting “at the top” with higher level cognitive processes (such as expectations and knowledge) and then “working down” Conceptually driven processing that moves from the whole to the parts Ex: you have ingredients and must put them together to make something edible Ex: you have ingredients and a recipe & picture of a completed cake and you must recreate the cake

4 Top-Down Processing example
Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

5 Sensation- Thresholds
Absolute Threshold minimum stimulation needed to detect a particular stimulus usually defined as the stimulus needed for detection 50% of the time Difference Threshold minimum difference between two stimuli that a subject can detect 50% of the time just noticeable difference (JND) increases with magnitude Ex: listen to headphones and indicate the earliest you hear a tone Ex: listen to headphones and indicate when you hear a change in volume of sound Easier to tell the difference between 4 & 5Hz than 1000 & 1001Hz

6 Sensation- Thresholds
Signal Detection Theory predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise) assumes that there is no single absolute threshold detection depends partly on person’s -experience -motivation -expectations -level of fatigue

7 Sensation- Thresholds
25 50 75 100 Low Absolute threshold Medium Intensity of stimulus Percentage of correct detections Subliminal stimuli When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”.

8 Vision Transduction: conversion of one form of energy to another
Did you know major league batters can hit a 90 mile per hour fastball 4/10 of a second after it leaves the pitcher’s hand? Transduction: conversion of one form of energy to another Wavelength: the distance from the peak of one wave to the peak of the next Hue: dimension of color determined by wavelength of light Intensity: amount of energy in a wave determined by amplitude brightness loudness

9 Vision: Parts of the Eye
Cornea: transparent covering on the front of the eye Fovea: central point of focus on the back of the eye Pupil: adjustable opening in the center of the eye Iris: a ring of muscle the forms the colored portion of the eye around the pupil and controls the size of the pupil opening Lens: transparent structure behind pupil that changes shape to focus images on the retina Accommodation: change in shape of lens focus near objects Retina Layers of neurons on inner surface of eye light sensitive contains rods and cones beginning of visual information processing Blind Spot: area of retina where optic nerve leaves back of eye

10 Vision: Parts of the Eye

11 Retina’s Reaction to Light Receptors
Cones near center of retina (fovea) fine detail and color vision daylight or well-lit conditions Rods Located in periphery of retina detect black, white and gray twilight or low light Receptors in the Human Eye Cones Rods Number Location in retina Sensitivity in dim light Color sensitive? Yes Low Center 6 million No High Periphery 120 million

12 Pathways from the Eyes to the Visual Cortex

13 Vision Acuity: the sharpness of vision Nearsightedness Farsightedness
nearby objects seen more clearly lens focuses image of distant objects in front of retina Farsightedness faraway objects seen more clearly lens focuses near objects behind retina Farsighted Nearsighted Normal Vision Vision Vision

14 Color-Deficient Vision
People who suffer red-green blindness have trouble perceiving the number within the design

15 Visual Information Processing
Feature Detectors neurons in the visual cortex respond to specific features shape angle movement Stimulus Cell’s responses Parallel Processing simultaneous processing of several dimensions through multiple pathways color motion form depth

16 Visual Information Processing
Scene Retinal processing: Receptor rods and conesbipolar cells  ganglion cells Feature detection: Brain’s detector cells respond to elementary features-bars, edges, or gradients of light Abstraction: Brain’s higher-level cells respond to combined information from feature-detector cells Recognition: Brain matches the constructed image with stored images

17 Visual Information Processing
Trichromatic (three color) Theory Young and Helmholtz The eye contains three different types of cones capable of responding to various wavelengths of light red green blue

18 Visual Information Processing
Opponent-Process Theory: opposing retinal processes enable color vision “ON” “OFF” red green green red blue yellow yellow blue black white white black

19 How the Brain Perceives

20 Visual Perception: Gestalt
Gestalt Principles (gestalt = an organized whole. We tend to integrate pieces of info. into meaningful wholes) Proximity Simplicity (law of good form) Connectedness Closure Continuity Similarity Phi Phenom

21 Visual Perception: Depth
Depth Perception: The Visual Cliff Binocular Cues: clues about distance based on the differing views of the two eyes Retinal Disparity: the fact that the right and left eyes see slightly different views of the object Convergence: the degree to which the two eyes must converge to focus on the object Monocular Cues: clues about distance based on the image in either eye Linear Perspective: parallel lines converge in the distance Relative Size: if two objects are the same, the larger one is seen as closer Interposition: the nearer object overlaps the object farther in the distance Texture Gradient: textures are coarser the closer they are Light and shadow Height in plane

22 Pictorial depth cues

23 Visual Perception: Constancies
Perceptual Constancies: the ability to experience a constant perception even when what is reflected on the retina changes Color: an object will be perceived as the same color even if the color reflected on the retina changes (ex: when an object is placed in the shade) Size: an object will be perceived as the same size even if the size reflected on the retina changes (ex: dog running toward you is not seen as growing in size) Shape: an object will be perceived as the same shape even if the shape reflected on the retina changes (ex: door opening toward you is still perceived as rectangular)

24 Perceptual Constancies: Size,Shape,Brightness, Color

25 Perceptual Illusions

26 Illusions

27 The Intensity of Some Common Sounds

28

29 Audition: The Ear Outer Ear Middle Ear Inner Ear Auditory Canal
Eardrum Middle Ear hammer anvil stirrup Inner Ear oval window cochlea basilar membrane hair cells

30 Audition: Pitch Perception
Place Theory the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated Frequency Theory the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch

31 Body Position and Movement
Kinesthesis the system for sensing the position and movement of individual body parts Vestibular Sense the sense of body movement and body’s position relative to gravity including the sense of balance Semicircular canals in ears

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