Chapter 4 Sensation and Perception PDF

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CHAPTER 4: SENSATION AND PERCEPTION ❖ Sensation: the stimulation of sense organs ➢ Involves the absorption of energy such light/sound waves, by sensory organs of the eyes and ears ❖ Perception: the selection, organization, and interpretation of sensory input ➢ Involves organizing and translating sensory input into something meaningful

Psychophysics: Basic Concepts and Issues ❖ Psychophysics: the study of how physical stimuli are translated into psychological experience ❖ Gustav Fechner (1860) ❖ THRESHOLDS: LOOKING FOR LIMITS ➢ Sensation begins with a stimulus, any detectable input from the enviornment ➢ Fechner wanted to know ■ Question: For any given sense, what is the weakest detectable stimulus? ■ Answer: threshold. ● Threshold is a dividing point between energy levels that do and do not have a detectable effect ● Ex. hardware stores sell a gadget with a photocell that automatically turns a lamp on when a room gets dark. The level of light intensity at which the gadget clicks on is

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its threshold. ➢ Absolute threshold: for a specific type of sensory input is the minimum amount of stimulation that an organism can detect ■ Define the boundaries of an organism’s sensory capabilities ■ As stimulus intensity increases, subject’s probability of responding to stimuli gradually increases ● NEW DEFINITION: absolute threshold as the stimulus intensity detected 50% of the time ■ TABLE 4.1→ EXAMPLES ❖ WEIGHT THE DIFFERENCES: THE JND ➢ A just noticeable difference (JND): is the smallest difference in the amount of stimulation that a specific sense can detect. ➢ An AT is simply the JND from nothing (no stimulus input) ➢ Vary by sense ➢ Weber’s Law: states that the size of a JND is a constant proportion (weber’s fraction) of the size of the initial difference ■ Applies to all senses ■ Ex. WF (1/30) for weight. So one cannot detect the difference b.w 300g and 310g, because the JND of 300 is 10g. One can detect the difference b.w 900g and 910g, because the JND of 900g is 30g. ■ As stimuli increase in magnitude, the JND becomes larger ❖ PSYCHOPHYSICAL SCALING ➢ Ex. if one light has twice the energy of another, do you necessarily perceive it as being twice as bright? ■ Asking to scale the magnitude of sensory experience

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➢ Fechner’s Law: states that the magnitude of a sensory experience is proportional to the # of JND’s that the stimulus causing the experience is above the AT ■ Magnitude = #of JND’s / Absolute threshold ■ Ramification: constant increments in stimulus intensity (the amount of light) produce smaller and smaller increases in the perceived magnitude of sensation (perceived brightness) ➢ CONCLUSION: perception cannot be measured on absolute scales , everything is relative ❖ SIGNAL DETECTION THEORY ➢ SDT: proposes that the detection of stimuli involves decision processes as well as sensory processes which are both influenced by a variety of factors besides stimulus intensity ➢ SDT replaces Fechner’s sharp threshold w/ concept of “detectability” ■ Which is measured in terms of probability and depends on decision-making processes as well as sensory processes ❖ PERCEPTION WITHOUT AWARENESS ➢ Question: Can sensory stimuli that fall beneath the threshold of awareness still influence behaviour? ■ Subliminal perception: the registration of sensory input w/o conscious awareness (subliminal=below threshold) ■ “EAT POPCORN” example ➢ Subliminal inputs can produce measurable, although small, effects in subjects who subsequently report that they did not consciously register the stimuli ➢ Produces weak effects

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❖ SENSORY ADAPTATION ➢ SA: is a gradual decline in sensitivity due to prolonged stimulation ■ Jumping in a pool of water, trash smelling ➢ SA is automatic, built-in process that keeps ppl tuned into changes rather the constants in their sensory input ➢ Probably a behavioural adaptation that been sculpted by natural selection

Our Sense of Sight: The Visual System ❖ The Stimulus: Light ➢ Light is a form of electromagnetic radiation that travels as a wave ➢ Amplitude (height) → perception of brightness ➢ Wavelength (distance b.w peaks) → perception of color ➢ Purity (how varied the mix is) → perception of saturation, richness in colours ❖ The Eye: A living optical instrument ➢ Two purposes ■ Channel light to the retina (neural tissue that receives it) ■ House the retina ➢ Cornea→ “transparent window” ■ Func: where light enters the eye ➢ Lens→ transparent eye structure ■ Func: focuses the light rays falling on the retina ■ Accommodation occurs when the curvature of the lens adjusts to alter visual focus ● Close object→ lens gets fatter (rounder) ● Far object→ lens get flatter

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■ Nearsightedness: close objects are seen clearly but distant objects appear blurry ● Problem: cornea/lens bends light too much, eyeball too long ■ Farsightedness: distant objects are seen clearly but close objects appear blurry ● Problem: eyeball too short ➢ Pupil: opening in in the center of the iris ■ Func: helps regulate the amount of light passing into the rear chamber of the eye ■ constricts→ less light into eye, sharpens image ● In bright light ■ Dilates (opens) → more light into eyes, less sharp ● In dim light ➢ Saccades: rapid eye movements ■ Used to measure ● Gaze direction and attention ● Strength of visual distractors ● Detect deterioration in visual inhibitory activity (elderly ppl) ❖ The Retina: The brain’s envoy in the eye ➢ Retina: neural tissue lining the inside back surface of the eye ■ Function: ● Absorb light ● Process images ● Sends visual info to the brain

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➢ Optic disk: a hole in the retina where the optic nerve fibres exit the eye (blindspot) ➢ Visual Receptors: Rods and Cones ■ Cones: role in daylight vision and colour vision ● Stubbier ● 5-6.4 million (rods are more) ● Provide better visual acuity→ sharpness and detail ● Fovea: tiny spot in the centre of the retina that contains only cones ◆ Visual acuity is the greatest here ■ Rods:role in night vision and peripheral vision ● Elongated ● 100-125 million, most concentrated in the eye ● More sensitive to dim light ➢ Dark and Light adaptation ■ Dark Adaptation: the process in which the eyes become more sensitive to light in low illumination ■ Light Adaptation: the process whereby the eyes become less sensitive to light in high illumination ■ Walking into a dark movie theater (DA) walking out of the movie (LA) ■ Due to chemical changes in rods/cones, neural changes in receptors and elsewhere in retina ➢ Information Processing in the Retina: ■ Receptive field of a visual cell is the retinal area that, when stimulated, affects the firing of that cell

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● Comes in variety of shapes and sizes ● Circular fields with centre-surround arrangement ◆ Light falling in the center has an opposite effect of light falling in surrounding area ■ Lateral antagonism occurs when neural activity in a cell opposes activity in surround cells ● Allows the retina to compare the light falling in a specific area against general lighting ● Pays attention to contrast ● 4.13 illusion→ black square boxes, dots in white lines, when one concentrates in one area, one cannot see the black dot ❖ Vision and the Brain ➢ Visual Pathways to the Brain ■ Optic chiasm: the point at which the optic nerves from the inside half of each eye cross over and then project the opposite half of the brain ■ Optic nerve diverge along 2 pathways ● Main pathway projects into thalamus ◆ 90% of axons from retina SYNAPSE in the lateral geniculate nucleus (LGN) ◆ Visual signals processed in LGN then sent to primary visual cortex ◆ Subdivided into 2 pathways ➢ Mangocellular channel→ processes info regarding brightness (amplitude) ➢ Parvocellular channel→ perception of

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colour (wavelength) ➢ Parallel processing: involves simultaneously extracting different kinds of info from the same input ● Second pathway: branches off to are in the midbrain called the superior colliculus before going to the thalamus and occipital lobe ◆ Func: the coordination of visual input with other sensory input ➢ Information Processing in the Visual cortex ■ Hubel Wiesel (1979,1998,2005) ● Identified diff types of cells that respond to diff stimuli ● Simple cells→ respond best to a line of the correct width, correct angle, located in correct position in its receptive field ● Complex cells→ respond to width and orientation, respond to any position in RF ■ Feature detectors: neurons that respond selectively to very specific features of more complex stimuli ● Cells are highly specialized ■ After, input is routed to other cortical areas for additional processing, traveling through 2 streams ● Ventral stream→ processes details of what objects are out there (perception of form and colour) ◆ Neurons in this pathway can learn from experience ● Dorsal stream→ processes where the objects are (perception of motion and depth)

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■ Visual agnosia: an inability to recognize objects ■ Prosopagnosia: inability to recognize familiar faces ● Ppl compensate with heightened abilities to recognize voices ➢ McCollough effect→ get more info, confused?? ❖ Viewing the world in Colour ➢ The Stimulus for Colour ■ Lights with the longest wavelength appear red ■ Lights with the shortest wavelength appear violet ■ Two types of colour mixture ● Subtractive colour mixing: works by removing some wavelengths of light, leaving less light than was originally there ◆ Paints create this because pigments absorb most wavelengths (mixing blue and yellow to get green) ● Additive colour mixing: works by superimposing lights, putting more light in the mixture than exists in any one light by itself ● Humans use additive colour mixing more ➢ Trichromatic theory of Colour vision ■ TCT: Holds that the human eye has 3 types of receptors with differing sensitivities to different light wavelengths ● Red, green, and blue light ■ Colour-blindness: variety of deficiencies in the ability to distinguish among colours ● More in males than females

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● Dichromats: make do with only two colour channels ◆ 3 types-red, green, blue (very rare) ◆ Support the notion that there are 3 channels for colour vision as proposed by TCT ➢ Opponent Process Theory of Colour vision ■ Complementary colours: pairs of colours that produce grey tones when mixed together ● If you stare at strong colour then look at a white background you’ll see an afterimage- a visual image that persists after a stimulus is removed ● The afterimage will be the complement of the colour you stared at ■ OPT: colour perception depends on receptors that make antagonistic responses to pairs of colours. 3 types ● Red vs. green ● Blue vs. yellow ● Black vs. white ■ Explains why ppl cant distinguish b.w both colours when colour blind ➢ Reconciling theories of colour vision ■ It takes both theories to explain colour vision ■ George wald → the eye has 3 types of cones (TCT) ■ Biological basis for OPT→ cells in retina, the LGN, and visual cortex respond in opposite ways to red vs. green, and blue vs. yellow ➢ Effects of colour on Behaviour ■ Colours can have automatic, unconscious effects on behaviour, 10

through two sources ● 1→ ppl learn associations based on certain colours being paired repeatedly with certain experiences ◆ Red ink to mark students, red lights/red signs to warn of danger ● 2→ over the course of human evolution, certain colours may have had adaptive significance for survival or reproduction ◆ blood/fire: signal danger (Red) ❖ Perceiving forms, patterns, and objects ➢ Reversible figure: a drawing that is compatible with 2 interpertations that can shift back and forth (duck/rabbit, old woman/young woman, seal and master/woman and man) ■ Same visual input can result in radically diff. Perceptions ➢ Perceptual set: a readiness to perceive a stimulus in a particular way ■ Creates a certain slant in how someone interprets sensory input ■ Info about drawing “circus act w/ seal” before actually seeing image ➢ Inattentional blindness: the failure to see fully visible objects or events in a visual display ■ Basketball game w/ gorilla costume ■ Likelihood increases when ppl work on tasks that require a lot of attention or create a heavy perceptual load ➢ Feature Analysis: Assembling Forms ■ FA: the process of detecting specific elements in visual input and assembling them into a more complex form ● Bottom-up processing: a progression from individual

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elements to the whole ◆ Detect specific features of stimulus→ combine specific features into more complex forms→ recognize stimulus ● Top-down processing: a progression from the whole to the elements ◆ Formulate perceptual hypothesis about the nature of the stimulus as a whole→ select and examine features to check hypothesis→ recognize stimulus ◆ Subjective contours: the perception of contours where none actually exist (fig 4.27 see the triangle but no physical edge) ❖ Looking at the Whole picture: Gestalt Principles ➢ Gestalt psychologists: the whole can be greater than the sum of its parts ■ phi phenomenon: the illusion of movement created by presenting visual stimuli in rapid succession ● A movie ➢ Figure and Ground ■ The figure is the thing being looked at ● More substance and shape ● Closer to the viewer ■ Ground is the background against which it stands ➢ Proximity: things that are close to one another seem to belong together ➢ Closure: ppl often group elements to create a sense of closure,

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completing figures that have gaps in them ➢ Similarity: ppl tend to group stimuli that are similar (fig. 4.29c) ➢ Simplicity: ppl tend to group elements that combine to form a good figure (fig. 4.29d→ overlapping rectangle and triangle, than 11 sided figure) ➢ Continuity: ppl’s tendency to follow in w.e direction they’ve been lead ■ Connect points resulting in straight or curved lines ➢ Formulating perceptual hypotheses ■ Distal stimuli: lie in the distance (world outside the body) ■ Proximal stimuli: the stimulus energies that impinge directly on sensory receptors ■ Perceptual hypothesis: an inference about which distal stimuli could be responsible for the proximal stimuli sensed ❖ Perceiving Depth or Distance: ➢ Depth perception: involves interpretation of visual cues that indicate how near or far away objects are ➢ 2 types: binocular and monocular ➢ Binocular Cues ■ BDC: are clues about distance based on differing views of the 2 eyes ● 3D movies ■ Retinal disparity: that objects project images to slightly different locations on the right and left retinas, so the right and left eyes see slightly diff views of the object ◆ Confused?? ■ Convergence: involves sensing the eyes converging toward each other as they focus on closer objects 13

➢ Monocular Cues ■ MDC: clues about distance based on the image in either eye alone. ● 2 types ◆ Motion parallax: involves images of objects at different distances moving across the retina at different rates ➢ Driving along a highway fence posts along the road appear to move more rapidly than trees in the distance ◆ Pictorial depth cues: clues about distance that can be given in a flat picture ➢ Linear perspective: lines converge in the distance ➢ Texture gradient ➢ Interposition: object comes b.w you and another object, it must be closer to you ➢ Relative size: closer objects appear larger ➢ Height in plane: distant objects appear higher ➢ Light and shadow ➢ Judgements in distance can be highly subjective ❖ Perceptual Constancies in vision ➢ Perceptual Constancy: a tendency to experience a stable perception in the face of continually changing sensory input ■ Person approaching from a distance her image on your retinas

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gradually changes in size but we don't perceive that the person is growing in front of us ➢ The power of misleading cues: Optical illusions ■ OI: involves an apparently inexplicable discrepancy b.w the appearance of a visual stimulus and its physical reality ● Muller-lyer illusion ■ Impossible figures: objects that can be represented in 2-D pictures but cannot exist in 3D space ● 3 classic figures fig 4.41 ➢ Vision for Perception and Vision for Action ■ Vision serves 2 functions ● VFP: to create an internal representation or model of the external world ◆ Ventral stream ● VFA: process of controlling your actions that are directed at those objects ◆ Avoiding obstacles and correcting for changes in location in the target you are reaching for ◆ Dorsal stream

Our Sense of Hearing: The Auditory System ❖ Distal stimulus (a screech of tires) produces a proximal stimulus in the form of sound waves reach the ears ❖ The Stimulus: Sound ➢ Sound waves= the vibrations of molecules traveling through air ➢ Generated by : ■ Vibrating objects (guitar stirng, vocal cords, loudspeaker cone)

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■ Forcing air past a chamber (through a pipe organ) ■ Releasing a burst of air (when clapping) ➢ Sound waves physical properties affect perceived qualities ■ Wavelength (frequency) → pitch ■ Amplitude→ loudness ■ Purity→ timbre ❖ Human Hearing Capacities ➢ Wavelengths→ frequency (Hz) ■ High frequency = high pitch ➢ Pitch is also influenced by the amplitude of sound waves ➢ Humans can hear sounds 20Hz--20000Hz ➢ Amplitude measured in decibels (dB) ■ Greater the amplitude the louder the sound ➢ Loudness depends on interaction b.w amplitude and frequency ➢ Timbre ■ Purity (complexity of a sound) ● Purest sound is one with a single freq. Of vibrations (tuning fork) ■ Note with the same loudness and pitch played on a french horn and then on a violin→ the difference you perceive in the sounds is the difference in timbre ❖ Sensory Processing in the Ear ➢ Ear is divided into 3 sections and sound is conducted differently in each ■ External ear→ depends on vibration of air molecules ● Pinna- sound collecting cone ● Auditory canal-funnel sound waves to eardrum 16

● Eardrum- taut membrane that vibrates in response ■ Middle ear→ depends on the vibration of movable bones (ossicles) ● Ossicles ◆ Hammer ◆ Anvil ◆ Stirrup ● Three-stage lever system ● amplify tiny changes in air pressure ■ Inner ear→ depends on waves in a fluid ● Cochlea- a fluid-filled, coiled tunnel that contains the receptors for hearing ◆ Sound enters here through oval window vibrated by the ossicles ● Basilar membrane-runs the length of the spiralled cochlea, holds the auditory receptors (via retina in the eye) ◆ Divides cochlea into upper and lower chambers ● Auditory receptors= hair cells ● Waves in the fluid stimulate the hair cells ● Hair cells convert physical stimulation→ neural impulses sent to brain ■ Signals sent to thalamus→ auditory cortex in temporal lobe ❖ Auditory Perception: Theories of Hearing ➢ 2 theories on pitch perception ■ Place Theory: perception of pitch corresponds to the vibration of different portions, or places, along the basilar membrane 17

● Hair cells at different locations respond independently ● Different sets of hair are vibrated by different frequencies ● Brain detects freq of a tone depending on which area of basilar membrane is most active ■ Frequency Theory: perception of pitch corresponds to the rate, or frequency, at which the entire basilar membrane vibrates ● Whole membrane vibrates in unison in response to sounds ● brain detects freq of a tone by the rate which the auditory nerve fibres fire ➢ Rencolining both theories ■ Both turned out to be valid in part ■ Low freq tones are translated to pitch through freq theory ■ High freq tones are translated to pitch through place theory ■ Complex freq tones use both ❖ Auditory Localization: Perceiving sources of sound ➢ Auditory localization: locating the source of sound in space ➢ 2 cues are important: ■ Intensity (loudness) ■ Timing ■ Of sounds arriving in each ear ➢ The loss of sound intensity due to distance ➢ Sound shadow caused by the head can affect the cues ❖ Music and its effects ➢ Temporarily affect our moods ➢ Increase our ability to perform certain tasks

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➢ Correctly identify emotions in the speech of others ■ Speech prosody: melody and rhythm

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