Chapter 4 - Perception PDF

CHAPTER 4: PERCEPTION  SENSATION VS. PERCEPTION Sensation Input about the physical world obtained by sensory receptors Perception The process by which the brain selects, organizes, and interprets sensations Senses are the physiological basis of perception...

CHAPTER 4: PERCEPTION  SENSATION VS. PERCEPTION Sensation Input about the physical world obtained by sensory receptors Perception The process by which the brain selects, organizes, and interprets sensations Senses are the physiological basis of perception Transduction The process where sensations are translated to electrochemical transmission of the brain  SENSATION VS. PERCEPTION External world: Internal world: The 5 senses ‘Other’ senses Vision/sight Proprioception (kinesthetic sense) Nociception Hearing/audition Equilibrioception (vestibular sense) Touch/tactile Smell/olfaction Taste/gustation  PERCEPTION AS INFERENCE Sensation Vibrations on the hair follicles in my ear Perception A baby is crying PERCEPTION AS INFERENCE PERCEPTION AS INFERENCE  INVESTIGATING SENSATION & PERCEPTION Psychophysics Evaluates how the physical experience of sensation is translated into perception  THEORIES OF PERCEPTION Information is gathered by the senses and sent to the brain for further processing Constructive Perception The brain’s attempt to construct a model of the external world based on sensory input Sensory Perception Mental Model Action Organs receive signals from the The brain infers a model based Behavior based on inferred environment. on sensory input. model of environment, not the stimuli themselves.  THEORIES OF PERCEPTION Direct Perception Behavior is directly based on sensory input from the environment without the construction of a mental model  AMBIGUITY OF STIMULI Constructive Perception Sensory data is used as evidence to construct the 3D external world What we perceive is a construction of the brain  VISUAL ILLUSIONS Examples of ambiguous stimuli The brain consistently guesses incorrectly  BI-STABLE IMAGES What happens when the brain changes its mind… BI-STABLE IMAGES BI-STABLE IMAGES BI-STABLE IMAGES BI-STABLE IMAGES  GESTALT PSYCHOLOGY “The sum is greater than the whole of its parts” People perceive and process information as organized wholes, rather than individual parts Perception is more complicated than assembling messages like pieces of a puzzle  GESTALT GROUPING PRINCIPLES Figure-ground Determines foreground and background Similarity Similar objects are grouped together Proximity Elements are perceived as a group when they’re close together Continuity (Good continuation) Elements are grouped when they align with each other Closure We fill in the gaps or connect the dots to complete implied shapes or images Common fate Objects moving together are grouped together FIGURE/GROUND ASSIGNMENT GESTALT GROUPING PRINCIPLES: SIMILARITY GESTALT GROUPING PRINCIPLES: PROXIMITY GESTALT GROUPING PRINCIPLES: CONTINUITY GESTALT GROUPING PRINCIPLES: CLOSURE GESTALT GROUPING PRINCIPLES: COMMON FATE  THE VISUAL SYSTEM ~20% of the cortex is involved in visual processing  THE EYE Light: Cornea → Iris → Pupil → Retina Images are flipped on the retina Perspective projection  THE EYE: THE RETINA Photoreceptors Rods High sensitivity Low spatial resolution Achromatic Cones Lower sensitivity High resolution Chromatic  THE EYE: OPTIC NERVE Optic nerve Axons of neurons that exit through the back of the eye Blind spot FINDING YOUR BLIND SPOT FINDING YOUR BLIND SPOT  THE VISUAL BRAIN Lateral geniculate nucleus (LGN) 90% of visual information sent to the thalamus The visual system is largely hierarchical Neurons respond to more complex and more specific properties the higher up you go in the system Primary visual cortex (V1) Neurons respond to simple patterns Higher up areas Neurons respond to complex shapes and specific features  THE VISUAL BRAIN Retinotopic organization Neurons with receptive fields close together in visual space have cell bodies close together in the cortex  VISUAL CORTEX: FUNCTIONAL LOCALIZATION Visual agnosia Difficulty recognizing or perceiving one kind of visual stimulus while maintaining the ability to process other kinds of stimuli Prosopagnosia Difficulty recognizing individual faces Semantic agnosia Difficulty recognizing everyday objects  VISUAL CORTEX: FUNCTIONAL LOCALIZATION Fusiform Face Area (FFA) Shows greater activity when people engage in a facial recognition task Lateral Occipital Cortex (LOC) Selectively activated when people do an object recognition task FUNCTIONAL LOCALIZATION: GREEBLES!  DORSAL & VENTRAL STREAMS Dorsal stream (Where) Occipital lobe → parietal lobe Projects upward Ventral stream (What) Occipital lobe → temporal lobe Projects downward  DORSAL & VENTRAL STREAMS GOODALE & MILNER (1991) Ventral stream damage (Perception) Unable to verbally match lines Able to physically match lines Dorsal stream damage (Action) Able to verbally match lines Unable to physically match lines  VISUAL PERCEPTION: PROCESSING Bottom-up processing No specific knowledge of the stimulus required Top-down processing Specific knowledge of a stimulus affects how it is perceived Previous experience/expectation BOTTOM-UP VS. TOP-DOWN PROCESSING BOTTOM-UP VS. TOP-DOWN PROCESSING BOTTOM-UP VS. TOP-DOWN PROCESSING BOTTOM-UP VS. TOP-DOWN PROCESSING BOTTOM-UP VS. TOP-DOWN PROCESSING VISUAL PERCEPTION: PROPERTIES OF VISUAL STIMULI Image segmentation Dividing an image into different object and regions Depth perception Images are 2D, but where are they in 3D? Object recognition What is this? Image Segmentation Depth Perception Object Recognition  IMAGE SEGMENTATION Bottom-up approach  IMAGE SEGMENTATION Bottom-up & top-down approach  DEPTH PERCEPTION Cues to depth perception Occlusion (object blocking) Objects that block other objects are assumed to be in front Motion parallax Objects farther away from you will change their position more slowly on your retina as you move  DEPTH PERCEPTION: BINOCULAR DISPARITY Our 2 eyes have different perspectives of the world Binocular disparity The difference in position of an object on the retina of each eye The amount of disparity changes as a function of how far away an object is from where you’re fixating DEPTH PERCEPTION: BINOCULAR DISPARITY  STEREOPSIS The perception of depth based on the difference in disparity between the 2 eyes  OBJECT RECOGNITION What objects are in the scene? Incoming stimuli matched to stored representations in memory  OBJECT RECOGNITION: HOW? Template model Match input to a stored image Simplest approach, very inflexible  OBJECT RECOGNITION: HOW? Identification The ability to identify the same object across variations  OBJECT RECOGNITION: HOW? Classification Recognizing something as a member of a category, even if you’ve never seen that specific stimulus  OBJECT RECOGNITION: HOW? Feature-based recognition Some features of objects remain common across different views and examples  OBJECT RECOGNITION: CONTEXT Objects rarely appear out of context Provides important information for recognition Biederman (1972) Congruent context leads to faster accuracy in object recognition  OBJECT RECOGNITION: SCENE SCHEMAS Individuals learn which objects tend to appear in particular contexts Barenholtz (2014) How much does contextual information contribute to recognition? No context/unfamiliar context/familiar context  HEARING & SOUND Sound: Pinna → Ear canal → Eardrum → Ossicles → Cochlea Cochlea Basilar membrane Hair cells Mechanoreceptors  HEARING & SOUND: THE COCHLEA Tonotopic organization A functional map that represents sound properties in the brain by showing how different sound frequencies are processed in different spatial locations  THE AUDITORY CORTEX Medial geniculate nucleus (MGN) Where components of sound are organized and analyzed Primary Auditory Cortex (A1) Neurons respond to specific stimuli Pitch and rhythm of soundwaves Dorsal stream (Where) Sound localization Ventral stream (What) Sound identification  SOUND LOCALIZATION Binaural cues Require input from both ears The brain compares information from both ears Interaural time differences Comparisons made between the small differences in arrival time of a sound in each ear Interaural level differences Comparison of the intensity differences of sound as it arrives in each ear  SPEECH PERCEPTION: THE MCGURK EFFECT McGurk & Donald (1976)  THE CHEMICAL SENSES: SMELL & TASTE Chemoreceptors Respond to properties in air molecules interpreted as smell and taste Olfaction Sense of smell Measures chemicals moving through the air Gustation Sense of taste Measures chemicals that have been ingested  THE OLFACTORY SYSTEM Nostrils & throat → Olfactory epithelium (olfactory mucosa) → Olfactory bulb Olfactory receptor neurons Sensitive to specific odorants Over 350 olfactory receptor types  THE GUSTATORY SYSTEM Mouth → Taste buds → Primary gustatory cortex 5 types of receptors Sweet Sour Salty Savory Bitter  THE CHEMICAL SENSES & EATING Flavor A combination of olfactory and gustatory perception Smell contributes more to flavor than taste  SKIN & BODY SENSES: TOUCH Mechanoreceptors → Spine → Somatosensory cortex 4 kinds of tactile receptors Somatotopic organization Two adjacent points on your skin are represented by adjacent points on the somatosensory cortex  STIMULUS DETECTION Absolute threshold The level of intensity required to detect a stimulus 50% of the time ------ ------ ------ ------ ------ ------ ------  STIMULUS DETECTION Difference threshold The smallest amount of a particular stimulus required for a difference in magnitude to be detected Just noticeable difference (JND) Weber’s Law The ability to notice the difference between two stimuli is a constant proportion of the intensity or size of the stimulus SIGNAL DETECTION THEORY (SDT) PROSOPAGNOSIA EXAMPLE