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Chapter 3 Basics of Perception and Awareness Sensation and Perception Basic Principles • Sensation: A process by which our sensory receptors and nervous system receive and represent stimulus energy. • Perception: A process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events. • The connection between sensation and perception is not 1 to 1, things are added and subtracted. Sensation and Perception Basic Principles • Bottom-Up Processing: Analysis that begins with the sense receptors and works up to the brain’s integration of sensory information. • Top-Down Processing: Information processing guided by higher-level mental processes. – As when we construct perceptions drawing on our experience and expectations. – Schema: A mental representation that organizes knowledge about related concepts. Transduction: Conversion of one form of energy to another. In sensation, transforming of stimulus energies into neural impulses. Basic Issues in Perception Constructed or Direct? • Constructive View – Perceptions are “built” (i.e., constructed) – Mix of stimulus info, expectations, knowledge – Empiricist’s view • Direct View – Perceptions are based on uninterpreted information – Taken directly from environment – Nativist’s view Sensation and Perception Basic Principles Weber’s Work on Touch • Two-point Threshold: The smallest distance between two points of stimulation at which the two points are experienced as two points rather than one. – He used a compass-like device to simultaneously apply pressure to two points on the skin. – On Touch: Anatomical and Physiological Notes (1834) provided charts of the entire body in regards to the two-point threshold. Sensation and Perception Basic Principles Weber’s Work on Kinesthesis • Just Noticeable Difference (jnd): The sensation that results if a change in stimulus intensity exceeds the differential threshold. Sensation and Perception Basic Principles Psychophysics: Study of the relationship between the physical characteristics of stimuli and our psychological experience of them. Light: Lumens compared to brightness Sound: Decibels compared to loudness Temperature: BTU compared to warmth Taste: Grams of sugar compared to sweetness Sensation and Perception Basic Principles Judgments are Relative • The jnd is a constant fraction of the standard weight. – For lifted weights it is about 1/40, for non- lifted weights it is about 1/30 • Weber's Law: Just noticeable differences correspond to a constant proportion of a standard stimulus. Sensation and Perception Basic Principles Weber’s Law DR k R • R = Reiz, the German word for stimulus, the standard stimulus. DR = The minimum change in R that could be detected. • k = constant (as seen earlier, k = 1/40 for lifted weights) Sensation and Perception Basic Principles Absolute Threshold • Absolute Threshold: The smallest amount of stimulation that can be detected by an organism. •When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”. Sensation and Perception Basic Principles Absolute Threshold • Vision-We can see 1 candle 30 miles away - (pretty low threshold!). • Audition–We can hear a watch tick 20 feet away. • Taste-We can taste 1 tsp. of sugar in 2 gallons of water. • Smell-We can smell 1 drop of perfume within a 3 room apartment. • Touch-We can feel the sensation of a bee wing dropped from 1 cm above your back. Sensation and Perception Basic Principles The jnd as a Unit of Sensation • The absolute threshold was useful, but only provided a single point of connection between the physical world and the psychological world. • Differential Threshold: The amount that stimulation needs to change before a difference in that stimulation can be detected. – Given a geometric increase in the level of stimulus, there will be an arithmetical increase in the level of sensation. • S = k log R Sensation and Perception Basic Principles Estimates of Weber Constants Electric Shock Very Small Pitch .003 = 1/333 Deep Pressure .013 = 1/77 Visual Brightness .016 = 1/62 Weight .050 = 1/20 Loudness .088 = 1/11 Smell, Rubber .104 = 1/10 Cutaneous Pressure .136 = 1/7 Taste, saltiness .200 = 1/5 Sensation Light Energy • Wavelength: The distance from the peak of one light or sound wave to the peak of the next. • Light also exhibits properties of particles. • Intensity: Amount of energy in a wave; determined by the wave’s amplitude. Sensation Light (Electromagnetic) Energy Hue: Determined by wavelength, color we experience Sensation The Eye Sensation The Eye Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina. Retina: The light-sensitive inner surface of the eye, containing receptor rods and cones plus layers of neurons that begin the processing of visual information. Sensation The Eye Rods: Peripheral retina receptors Detect black, white and gray For peripheral or twilight conditions Cones: Receptors near center of retina Fine detail and color vision For daylight or well-lit conditions Sensation The Eye Optic Nerve: Nerve that carries neural impulses from the eye to the brain. Blind Spot: Point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there. Audition- The Ear Sensation Audition How Transduction happens • Hair cells are the nerve cells – Changes in the air pressure (the stimulus) – affect the fluid in the cochlea – the basilar membrane ripples (an undulating wave) – wave causes hair cells to bend and – trigger neural impulse – nerve impulse is sent to thalamus and temporal lobe's auditory cortex and we hear. • TRANSDUCTION IN HEARING IS MECHANICAL - FROM VIBRATIONS Pattern Recognition • Pattern Recognition: Step between transduction and perception of a stimulus in the environment and its categorization as a meaningful object. – Identifying an image in sensory memory by drawing on past experience or knowledge . • Agnosia: Patients suffering lesions in certain areas of the brain can see objects, but not recognize them. Pattern Recognition Visual Information Processing Pattern Recognition Visual Information Processing • Feature Detectors: Nerve cells in the brain that respond to specific features of the stimulus • shape • angle • movement Pattern Recognition Visual Information Processing • Geons are simple 3-dimensional forms such as spheres, cubes, cylinders, cones or wedges. One theory of object recognition, Recognition by Components (RBC) (Biederman, 1987), proposes that visual input is matched against structural representations of objects in the brain. These structural representations consist of geons and their interrelations (e.g., an ice cream cone could be broken down into a sphere located above a cone). Geons can be used to represent a large number of possible objects with very few components; e.g., 24 geons can be recombined to create over 10 million different two-geon objects. Pattern Recognition Visual Information Processing Pattern Recognition Visual Information Processing • Parallel Processing: Processing several aspects of a problem simultaneously. – The brain’s natural mode of information processing for many functions, including vision. Pattern Recognition Color Vision • Young-Helmholtz Trichromatic (three color) Theory – The retina contains three different retinal color receptors (cones)-one most sensitive to red, one to green, and one to blue-which when stimulated in combination can produce the perception of any color. Pattern Recognition Color Vision • People who suffer red-green blindness have trouble perceiving the number within the design. Pattern Recognition Color Vision • Opponent-Process Theory: Theory that opposing visual cortex processes (red-green, yellow-blue, white-black) enable color vision. • Some cells stimulated by green and inhibited by red. • Others stimulated by red and inhibited by green. Pattern Recognition Color Vision • So what is correct? • Both theories help explain color vision – Trichromatic theory explains color vision at the retina level. – Opponent-process theory explains color vision at the brain level. Pattern Recognition Hearing (Audition) Sound Localization Pattern Recognition Hearing (Audition) Perceiving Pitch • Place Theory – 1st theory of perceived pitch – Proposes we hear different pitches because different sound waves trigger activity at different places along the cochlea's basilar membrane. – Place theory only explains how we hear high pitch sounds. – High pitches close to oval window – Low pitches at far end of cochlea Pattern Recognition Hearing (Audition) Perceiving Pitch • Frequency Theory – Suggests we hear different pitches based on the frequency of the incoming sound waves – e.g.: 100Hz waves = 100 neural impulses/second – Unfortunately neurons cannot fire faster than 1000 times per second – This theory cannot account for hearing in the upper third of a piano key Pattern Recognition Hearing (Audition) Perceiving Pitch • Volley principle – Suggests that the neural cells can alternate firing and achieve a combined frequency above 1000 times per second • Actually, both place and frequency seem to influence perceived pitch Perception • Perception takes over where sensation stops • Perception is an active and constructive process of how we interpret and organize sensations • How the brain interprets and makes sense of incoming messages • There has been a philosophical debate since the beginning of philosophy. – Empiricists argue for nothing inborn – Nativists argue for inborn dispositions Perceptual Organization • Gestalt – An organized whole. – Tendency to integrate pieces of information into meaningful wholes. Perceptual Organization Form Perception Composed of several phenomenon – Figure ground – Grouping – Depth Perception – Perceptual constancy Perceptual Organization Form Perception Figure and Ground • Figure and Ground: Organization of the visual field into objects (figures) that stand out from their surroundings (ground). Perceptual Organization Form Perception Grouping • Grouping: The perceptual tendency to organize stimuli into coherent groups. • Grouping Principles – Proximity: group nearby figures together – Similarity: group figures that are similar – Continuity: perceive continuous patterns – Closure: fill in gaps – Connectedness: spots, lines and areas are seen as unit when connected Basic Tasks of Visual Perception Perceptual Organizational Processes • Global Precedence: We tend to notice wholes before parts. – Navon (1977) • Presented ambiguous stimuli • Had subjects identify local or global letters • Subjects were faster at identifying global element • Critical interaction: Conflict only interfered with identification of local element • Findings indicate primacy of noticing global features Perceptual Organization Form Perception Grouping Proximity Similarity Continuity Closure Connectedness Perceptual Organization Depth Perception • Depth Perception – Ability to see objects in three dimensions – Allows us to judge distance Visual Cliff Perceptual Organization Perceptual Constancy • We perceive Objects in our world as stable and the environment as changing rather than the reverse • We perceive changes in shape, size, color, or brightness as a function of distance, lighting, or movement. – Size-familiar objects retain their size regardless of distance – Shape-familiar objects retain shape regardless of angle of view – Brightness-familiar objects retain their color despite differing illumination Perceptual Organization Perceptual Constancy Shape Constancy Perceptual Organization Perceptual Constancy Color Constancy Perceptual Organization Perceptual Constancy Color Constancy Perceptual Organization Perceptual Constancy Shape and Size Constancies Perceptual Organization Perceptual Constancy Shape and Size Constancies Size-Distance Relationship Perceptual Organization Perceptual Constancy Lightness Constancy Perceptual Organization Perceptual Constancy Lightness Constancy Perceptual Interpretation Two Conflicting Views • Immanuel Kant (Nature) – Knowledge comes from our inborn ways of organizing sensory experiences. • John Locke (Nurture) – Through our experience we also learn to perceive the world. Perceptual Interpretation Sensory Deprivation and Restored Vision • People born with cataracts can immediately sense colors and figure-ground distinctions after the cataracts removed, thus supporting Kant’s notion of innate perceptions. • However, these same people could not identify by sight those objects which they were familiar with by touch, thus supporting Locke’s notion of learned perception. Perceptual Interpretation Perceptual Set Context Effects • We often interpret ambiguous situations based on things around it. • In spoken language, homophones are totally ambiguous. – The window pane/pain was raised. • Standing alone, the word pane/pain is indistinguishable • In context, it is quite easy to determine Perceptual Interpretation Perceptual Set Context Effects Perceptual Interpretation Face Perception • Holistic Processing: Perceiving the whole object. • Analytic Processing: Perceiving the features which comprise the whole. – Oliver Sacks wrote a book titled The Man who Mistook his Wife for a Hat • Included story of a man who mistook his foot for a shoe. • Prosopagnosia: An inability to recognize faces while other visual recognition remains unchanged. • Module: A set of processes that are automatic, fast, encapsulated apart from other cognitive systems, and located in a localized area of the brain. Multi-Sensory Interaction and Integration Synesthesia • Synesthesia: Input from one sensory modality is experienced in another. – Strong synesthesia • Example: experiencing a smell as “pointy” – Weak synesthesia • Linguistic in nature • Example: Labeling colors as “cool” or “warm” Multi-Sensory Interaction and Integration Comparing the Senses • Vision tends to dominate the other senses – Vision and Audition • Ventriloquist Effect: Tendency for visual cues to influence localization of sound. • McGurk Effect: Visual cues can affect the way we hear speech sounds. Multi-Sensory Interaction and Integration Comparing the Senses • Vision tends to dominate the other senses – Vision and Chemical Senses • Visual cues can influence what we smell and taste. – Vision and Touch • Pavani, Spence and Driver (2000) found that visual cues can create illusions of touch. Consciousness Varieties of Consciousness • Consciousness refers to our awareness of internal and external events. • Varieties of consciousness – Monitoring Consciousness: Reflecting on one’s consciousness. – Self Consciousness: Knowledge about self. – Access Consciousness: Cognitive processes that subserve behavior. – Phenomenal Consciousness: Subjective experience. Consciousness Dissociations in Consciousness • Signal detection approach – Phenomenal reports of perception don’t always match reality. – Conscious perception is the product of: • Sensitivity (acuteness of perceptual processes) • Response bias (willingness to report) Consciousness Subliminal Perception • Subliminal Perception – Can stimuli below the threshold of conscious awareness influence behavior? • Marcel (1983) gave subjects a Stroop task – Responses were influenced by a subliminally presented color prime • Both inhibitory and excitatory priming found • Priming effects small Consciousness Subliminal Perception • Cheesman and Merikle distinguish between: – Subjective Threshold: Point at which subject claims not to have seen prime. • Can guess prime at above chance levels. – Objective Threshold: Point at which subject claims not to have seen prime. • Guessing of prime is no better than chance • Only primes presented below subjective threshold produce subliminal priming. Visual Attention Attentional Capture • Attentional Capture: A stimulus involuntarily captures visual attention. – Implicit: Changes some aspect of behavior. – Explicit: Leads to a conscious attention switch. Visual Attention Attentional Capture • Inattentional Blindness: Failure to notice obvious change in visual scene. – Sometimes termed change blindness – Simons and Chabris (1999) • Subjects watched and attended to a video • Over ½ failed to notice bizarre event Auditory Attention • Auditory attention is limited • Some conceive of attention as a gateway – We must select what receives attention – Studied with dichotic listening and speech shadowing – How do we attend?
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