SENSATION AND PERCEPTION CHAPTER 5
PSY100
SENSATION AND PERCEPTION CHAPTER 5 How do we sense our world?
Way we experience world: Sensation: The sense organs’ responses to external stimuli and the transmission of these responses to the brain - eg. Light, air vibrations, odors etc Perception: The processing, organization, and interpretation of sensory signals; it results in an internal representation of the stimulus. The essence of sensation is detection, the essence of perception is construction of useful and meaningful information about a particular environment Perception is often based on our prior experiences, which shape our expectations about new sensory experiences What we sense (see, hear, taste, touch or smell) is the result of brain processes that actively construct perceptual experiences and as a result, allow us to adapt to our environments’ details Stimuli Must be Coded to be Understood by the Brain Sensory Coding: our sensory organs’ translations of stimuli’s physical properties into neural impulses The brain cannot process raw stimuli, so the stimuli must be translated into chemical and electrical signals the brain can interpret Transduction: A process by which sensory receptors (specialized neurons in the sense organs) produce neural impulses when they receive physical or chemical stimulation Connecting neurons then transmit information to the brain in the form of neural impulses Most sensory information first goes to the thalamus, a structure in the middle of the brain Neurons in the thalamus then send information to the cortex, where incoming neural impulses are interpreted as sight, smell, sound, touch, or taste To function effectively, our brains need qualitative and quantitative information about a stimulus Coarse Coding: sensory qualities are coded by only a few different types of receptors, each of which responds to a broad range of stimuli
Psychophysics Relates Stimulus to Response
Sensory Thresholds: Absolute Threshold: the minimum intensity of stimulation that must occur before you experience a sensation, or the stimulus intensity detected above chance (eg. Absolute threshold for hearing is the faintest sound a person can detect) Difference Threshold: the just noticeable difference between two stimuli- the minimum amount of change required for a person to detect a difference (eg. Minimum change in volume for you to detect a difference) o Weber’s Law: states that the just noticeable difference between two stimuli is based on a proportion of the original stimulus rather than on a fixed amount of difference) Signal Detection Theory: A theory of perception based on the idea that the detection of a faint stimulus requires a judgment- it is not an all-or-none process Detecting a stimulus requires making a judgment about its presence of absence, based on a subjective interpretation of ambiguous information Response Bias: refers to a participant’s tendency to report detecting the signal in an ambiguous trial o higher level processes in the brain, such as beliefs and expectancies, influence how sensations from the environment are perceived Sensory Adaptation A decrease in sensitivity to a constant level of stimulation Sensory systems tuned to detect environmental changes If a stimulus is presented continuously, the responses of the sensory systems that detect it tend to diminish over time When a continuous stimulus stops, the sensory systems respond strongly as well
What are the basic sensory processes? In Taste, Taste Buds Detect Chemicals Gustation: The sense of taste To keep poisons out of our digestive system while allowing food in Taste buds: Sensory receptors that transduce taste information - When food stimulates taste buds, they send signals to the brain, which then produces the experience of taste - Every taste experience is composed of a mixture of 5 basic qualities: sweet, sour, salty, bitter, and umami (“savory” or “yummy”) - The entire taste experience happens not only in the mouth, but also the brain, which integrates these various sensory signals - Supertasters: highly aware of flavours and textures and are more likely than others to feel pain when eating very spicy foods - Taste preferences come from our different numbers of taste receptors
-
Cultural influences also affect food preferences, and your mother’s preferences (passed on to offspring)
In smell, the nasal cavity gathers odorants Olfaction: The sense of smell, which occurs when receptors in the nose respond to chemicals - Has the most direct route to the brain - We smell when chemical particles or odorants pass into the nose and when we sniff into the nasal cavity’s upper and back portions - In the nose and nasal cavity, odorants come into contact with: Olfactory Epithelium: The thin layer of tissue, within the nasal cavity, that is embedded with smell receptors - These receptors transmit information to the: Olfactory Bulb: The brain centre for smell, located below the frontal lobes - From here, smell information goes direct to other brain areas - Smell signals bypass the thalamus In touch, sensors in the skin detect pressure, temperature, and pain Haptic sense: the sense of touch - Conveys sensations of temperature, of pressure, and of pain and a sense of where our limbs are in space - Anything that makes contact with our skin provides tactile stimulation which gives rise to an integrated experience of touch - Haptic receptors for both temperature (separate hot and cold receptors) and pressure are sensory neurons that terminate in the skin’s outer layer - The integration of various signals and higher level mental processes produces haptic experiences Two types of pain - Warning system that stops you from continuing activities that may harm you - Actual experience of pain is created by the brain - Most pain experiences result when damage to the skin activates haptic receptors - Two kinds of nerve fibres identified with pain: o fast fibres for sharp, immediate pain o slow fibres for chronic, dull, steady pain - Important distinction between the fibres is the myelination or nonmyelination of their axons, which travel from the pain receptors to the spinal cord - Fast acting receptors activated by strong physical pressure and temperature extremes, slow acting receptors are activated by chemical changes in tissue when skin is damaged
Gate control theory - Past experiences are extremely important in determining how much pain a person feels - Gate Control Theory of Pain: states that for us to experience pain, pain receptors must be activated and a neural “gate” in the spinal cord must allow the signals through to the brain o Pain signals transmitted by small-diameter nerve fibres, which can be blocked at the level of the spinal cord (prevented from reaching the brain), by firing of larger sensory nerve fibres - Sensory nerves fibres can “close a gate” and prevent or reduce the perception of pain - Worrying about or focusing on the painful stimulus, seem to open the pain gates wider - Division of perception of pain in the brain: o One area responds to the sensory input from the part of the body that is in pain- the full pain of a chronic backache, the stabbing pain of cut and so on o Other part of the brain that is involved when we feel pain registers the emotional aspects of pain, which includes how unpleasant it is - When we feel pain, both areas of the brain are activated In hearing, the ear detects sound waves Audition: The sense of sound perception - Second source of information to world (vision first) - Hearing results when the movements and vibrations of objects cause the displacement of air molecules - These molecules produce a change in air pressure, and that change travels through the air Sound Wave: the pattern of the changes in air pressure through time that results in the percept of a sound - The wave’s amplitude determines its loudness; higher amplitude is perceived as louder - The sensory experience of hearing occurs within the brain, as the brain integrates the different signals provide by various sound waves Eardrum (tympanic membrane): A thin membrane, which sound waves vibrate, that marks the beginning of the middle ear - Our ability to hear is based on the intricate interactions of various regions of the ear, which convert sound waves into brain activity, producing the sensation of meaningful sound - Changes in air pressure produce sound waves that arrive at the outer ear and travel down auditory canal to eardrum - Eardrum vibrations are transferred to ossicles (3 tiny bones called the hammer, anvil, and stirrup)
-
Ossicles transfer the eardrums vibrations to the oval window, a membrane of the cochlea, or inner ear (fluid filled tube that curs into snail like shape) Pressure waves are created I the inner ears fluid and these waves prompt the hair cells to bend and cause neurons on the basilar membrane to fire Hair cells are the primary auditory receptors The mechanical signal of a sound wave hitting the eardrum is converted into a neural signal that travels to the brain via the auditory nerve
Locating sounds - Sound reaches the ear that is closest to the sound first, the it reaches the second ear (indicating that the source is closer to the other ear) In vision, the eye detects light waves - Very little of what we see takes place in the eyes, rather what we see results from constructive processes that occur throughout much of the brain to produce our visual experiences Cornea: The clear outer covering of the eye (where light first passes through) - Focuses on incoming light in a process called refraction - Light rays then enter and are bent farther inward by the lens which focuses the light to for an image on the retina Retina: The thin inner surface of the back of the eyeball. The retina contains the photoreceptors that transduce light into neural signal Pupil: The small opening in the eye; it lets in light waves - Determines how much light enters the eye through either contracting or dilating Iris: The coloured muscular circle on the surface of the eye; it changes the shape to let in more or less light -
The lens and cornea work together to collect and focus light rays reflected from an object, to form on the retina an upside-down image of the object
Rods and Cones - The retina has two types of receptor cells; Rods: Retinal cells that respond to low levels of illumination and results in backand-white perception (night vision) Photo pigments: light sensitive chemicals that initiate the transduction of light waves into electrical neural impulses Cones: Retinal cells that respond to higher levels of illumination and result in colour perception
Fovea: The centre of the retina, where cones are densely packed Transmission from the eye to the brain - After light is transduced into neural impulses by rods and cones, other cells in the retina- bipolar, amacrine, and horizontal cells- perform on those impulses a series of computations that help the visual system process the incoming information - Ganglion cells: the first cells in the visual pathway to generate action potentials o send their signals along their axons from inside the eye to the thalamus o these axons gathered into a bundle, the optic nerve, which exits the eye at the back of the retina o blind spot: the point at which the optic nerve exits the retina has no rods or cones (in each eye) - ganglion cells lying within the visual areas of the thalamus are transmitted to the primary visual cortex The detection of visual information - Particular visual neurons respond best to particular colours, shape orientations, or directions of motion Receptive Field: The region of visual space to which neurons in the primary visual cortex are sensitive - Visual receptive fields can be thought of as being located on a specific region of the retina or a specific location in visual space Lateral inhibition Lateral Inhibition: A visual process in which adjacent photoreceptors tend to inhibit one another - Our visual systems are sensitive to edges because edges tell us where objects end The colour of light is determined by its wavelength - Not seeing colours, but seeing the light waves that objects reflect to our eyes - Visible light consist of electromagnetic waves and the colour of light is determined by the wavelengths of the electromagnetic waves that reach the eye - We categorize colour along 3 dimensions: hue, brightness, and saturation - Hue: consists of the distinctive characteristics that place a particular colour in the spectrum - Brightness: colour’s perceived intensity, or luminance, which is determined chiefly by the total amount of light reaching the eye o a psychological dimensions that has no simple physical correlate; lightness is determined by its brightness relative to its surroundings - Saturation: a colour’s purity, or intensity- the vividness of the hue
Subtractive Colour Mixing: a way to produce a given spectral pattern in which the mixture occurs within the stimulus itself and is actually a physical, not psychological process (eg. Mixing paints) Colour is determined by mixture of wavelengths from a stimulus Colour can be produced in 2 ways: o Subtractive and additive mixture of wavelengths When we see a blue shirt, it is blue because the material the shirt is made from has absorbed medium and long wavelengths (yellow and red) and is reflecting only short wavelengths that are perceived as blue Red, yellow and blue are the subtractive primary colours, mix all together and you get black because these pigments absorb nearly all colours of the visible spectrum Additive Colour Mixing: a way to produce a given spectral pattern in which different wavelengths of lights are mixed. The percept is determined by the interaction of these wavelengths with receptors in the eye and is a psychological process. (stage lighting) When lights of different wavelengths are mixed what you see is determined by the interaction of the wavelengths within the eye`s receptors Any colour can be created by combining all 3 wavelengths Red, green and blue are the additive primary colours /mix all together to get white light Explaining Colour Vision: Colour is a product of our visual system and does not exist in the physical world There are 3 different cones in the retina-each responds to a different wavelength o One type is sensitive to blue light (Short ww) o Sensitive to green light (Medium ww) o Remaining cones are sensitive to red light (Long ww) o We see yellow because it stimulates L/M cones equally while not stimulating S Our perception of colour is determined by the ratio of activity among the three types of cone receptors To account for some colours seeming “opposite” to each other we must look at ganglion cells (second stage of visual processing) Different combinations of cones converge on the ganglion cells One type of ganglion cell may receive excitatory input from L cones (red) but may be inhibited by M cones (green) o This creates the perception that red and green are opposite Simultaneous Contrast: optical illusion in which identical stimuli appear different when presented against different backgrounds. (we are unaware of factors affecting our perception)
Humans and Animals have other Sensory Systems Kinesthetic sense: perception of our limbs in space; helps us co-ordinate movement Vestibular Sense: perception of balance; from receptors in the ear (we get sea sick or car sick when the vestibular system and the visual system conflict each other). Some animals have sonar sense and electroreception.
The Evidence for Extrasensory Perception (ESP) is weak/non-existent
(6th sense) communicate with ghosts, predict future, read minds Through experiments there is very little support for ESP Need to come up with empirical evidence to prove it or disprove it
What are the Basic Perceptual Processes Perception Occurs in the Brain Fig 5.32 The thalamus relays all sensory information to the cortical and other areas of the brain. Primary sensory areas: Hearing: Primary auditory cortex(A1, for the first auditory area), which is in the temporal lobe, different areas of it respond to different frequencies (high/low) Touch: Primary somatosensory cortex (S1), which is in the parietal lobe, areas with greater sensitivity have larger regions of S1 dedicated to them (lips) Vision: study of perception has focused to a large extent the on the visual cortex (believed that half of the cerebral cortex participates in visual perception in some way). Primary visual cortex (V1) is located in the occipital lobe. Some neurons in V1 have higher firing rates when particular orientations of lines are put before them. (may fire more if it is straight then if it is tilted at an angle/known as simple cells) Fig 5.33 What vs where: 2 parallel pathways from the occipital lobe: o Ventral Stream (what): specialized for perception and recognition of objects (determining colours and shapes) o Dorsal Stream (where): spatial perception o One can be damaged while other one works (a lady could not identify a picture of an apple but when told to draw an apple she could through memory; this is known as object agnosia-inability to recognize objects)
Object Perception Requires Construction One of the most important roles for V1 (primary visual area in the brain) is to extract the edges and contours that define the boundaries of objects. One of the 1st steps in processing a from appears to be encoding the features that compose it.
Gestalt Principles of Perceptual Organization: Theory that states that perception is more than the result of accumulating sensory data. States that our brains use innate (built-in) principles to organize sensory information. Proximity and Similarity: Principle of Proximity states that the closer two figures are to each other, the more likely we are to group them and them as part of the same object, Principle of Similarity states that we tend to group figures according to how closely they resemble each other (shape/colour) The “Best” Forms: Good continuation is the tendency to interpret intersecting lines as continuous rather that changing direction. We complete objects that are blocked from our view by an occluder. Closure refers to the tendency to complete figures that have gaps Fig. 5.35 Figure and Ground: Most basic organizing principles is distinguishing between figure and ground Bottom-Up Processing: a hierarchical model of pattern recognition in which data are relayed from one processing level to the next always moving to a higher level of processing Top-Down Processing: a hierarchical model of pattern recognition in which information at higher levels of processing can influence lower, “earlier” levels in the processing hierarchy o Because of these 2 types of processing, context affects perception , what we expect to see influence what we perceive Fig 5.36 Face Perception: Several studies support the idea that the human face reveals “special” information that is not available in any other way (mood, attentiveness, race, age) Specific regions of the brain (fusiform gyrus and even as specific as neurons)are very responsive to anything that looks like a face. Prosopagnosia is deficit in the ability to recognize races (you can still recognize objects/showing that they differ) Facial recognition supports the idea that the mind is adaptive (perceives anger on a man quicker than it does on a women because they commit most violent crimes). Own sex bias, women are most accurate when recognizing woman faces. We have a very hard time recognizing faces when they are inverted. Biological, Individual (females recognize faces better than males), Social (anger on a man’s face) and Cultural (own race bias) impacts of face recognition are apparent. Regaining Vision by Fixing the Eyes: “people see with their brains not with their eyes”. With todays’ technology people who become blind are able to regain their sight. Those who are blind for many years have much more difficulty restoring their vision after operation (corneal and stem cell implants), things like face recognition and depth perception. The brain is fine-tuned through experience, if a cortical region is not used it ceases to develop normally.
Depth Perception Is Important For Locating Objects Binocular Depth Cues: Cues of depth perception that arise from the fact that people have two eyes
The brain applies the same rules to both 2D and 3D objects by rapidly and automatically exploits prior assumptions it has about the nature of the relationship between 2 dimensional and 3 dimensional objects (cues) Binocular Disparity: a cue of depth perception that is caused by the distance between a person’s eyes, which provides each eye with a slightly different image, the brain has access to two different but overlapping images Stereoscopic Vision: ability to determine an object’s depth based on that object’s perception to each eye 5.42 Monocular Depth Cues: cues of depth perception that are available to each eye alone A three-dimensional array of objects creates exactly the same image on the retina that a photograph of the same array of objects does. (watching movies) o Occlusion: a near object blocks an object that is further away o Relative Size: far-off objects project a smaller retinal image than close objects do o Familiar Size: we know how large familiar objects are, so we can tell how far away they are by the size of their retinal images o Linear Perspective: parallel lines appear to converge in the distance o Texture gradient: as a uniformly textured surface recedes, the texture continuously becomes denser o Position Relative to horizon: objects below the horizon that appear higher in the visual field are perceived as being away. Objects above the horizon that appear lower in the visual field are perceived as being further away
Culture Influences Perception Do we automatically use picture cues or do we learn how to use them? If you were not raised in a “carpentered world” you would not know parallel lines seem to converge in the distance and therefore your culture influences your perception Kids who went to school and lived in rural areas are able to recognize illusions (Mueller-Lyer) than those that don’t Motion Cues for Depth Perception: Motion Parallax: is the relative movements of objects that are at various distances from the observer o Near objects pass quicker and objects that are further away seem to pass slower
Size Perception Depends on Depth Perception The size of an object’s retinal image depends on that object’s distance from the observer. Optical illusions can arise when normal perceptual processes incorrectly represent the distance between the viewer and stimuli-depth cues fool us into seeing depth when its’ not there.
Ames Box: diagonally cut room, with angled windows and tiles to produce an illusion. When one child is in one corner and a child of equal size is in the other, one appears as a giant Fig 5.49 The Ponzo Illsuion: size/distance illusion, monocular depth cues make the 2D figure seem 3D Fig 5.50
Motion Perception Has Internal and External Cues We have neurons specialized for detecting movement. 3 phenomena that offer insight into how the visual system perceives motion: Motion After Affects (water fall effect): occur when you look at a moving image for a prolonged period of time and then kook at a stationary scene, you see the second object as moving in the opposite direction as the than the first object. o Neurons get fatigued and less sensitive after period of time, so if scene changes other motion detectors respond Compensatory Factors: How do u know whether an object is moving or whether, you or your eyes are moving? Brain calculates an object’s perceived movements by monitoring the movement of the eyes, and perhaps also of the head, as they track a moving object. o Image Moving System and Eye Moving System Fig 5.52 Stroboscopic Movement: a perceptual illusion that occurs when two or more slightly different images are presented in rapid succession.
Perceptual Consistencies are based on Ratio Relationships
Perceptual Consistency: people correctly perceive objects as constant in their shape, size, colour, and lightness, despite raw sensory data that could mislead perception. Illusions occur when the brain creates inaccurate representations of stimuli To perceive any of the 4 consistencies, we need to understand the relationship between it and at least one other factor o Size Consistency: we need to know how far away the object is from us o Shape Consistency: we need to know from what angle we are seeing the object o Colour Consistency: we need to compare the wavelengths of light reflected from the object with those reflected from its background o Lightness Consistency: we need to know how much light is being reflected from the object and from its background Perceptual system is tuned to detect changes from baseline conditions, not just respond to sensory inputs Brain has built in assumptions that we can’t control
SENSATION AND PERCEPTION CHAPTER 5 How do we sense our world?
Way we experience world: Sensation: The sense organs’ responses to external stimuli and the transmission of these responses to the brain - eg. Light, air vibrations, odors etc Perception: The processing, organization, and interpretation of sensory signals; it results in an internal representation of the stimulus. The essence of sensation is detection, the essence of perception is construction of useful and meaningful information about a particular environment Perception is often based on our prior experiences, which shape our expectations about new sensory experiences What we sense (see, hear, taste, touch or smell) is the result of brain processes that actively construct perceptual experiences and as a result, allow us to adapt to our environments’ details Stimuli Must be Coded to be Understood by the Brain Sensory Coding: our sensory organs’ translations of stimuli’s physical properties into neural impulses The brain cannot process raw stimuli, so the stimuli must be translated into chemical and electrical signals the brain can interpret Transduction: A process by which sensory receptors (specialized neurons in the sense organs) produce neural impulses when they receive physical or chemical stimulation Connecting neurons then transmit information to the brain in the form of neural impulses Most sensory information first goes to the thalamus, a structure in the middle of the brain Neurons in the thalamus then send information to the cortex, where incoming neural impulses are interpreted as sight, smell, sound, touch, or taste To function effectively, our brains need qualitative and quantitative information about a stimulus Coarse Coding: sensory qualities are coded by only a few different types of receptors, each of which responds to a broad range of stimuli
Psychophysics Relates Stimulus to Response
Sensory Thresholds: Absolute Threshold: the minimum intensity of stimulation that must occur before you experience a sensation, or the stimulus intensity detected above chance (eg. Absolute threshold for hearing is the faintest sound a person can detect) Difference Threshold: the just noticeable difference between two stimuli- the minimum amount of change required for a person to detect a difference (eg. Minimum change in volume for you to detect a difference) o Weber’s Law: states that the just noticeable difference between two stimuli is based on a proportion of the original stimulus rather than on a fixed amount of difference) Signal Detection Theory: A theory of perception based on the idea that the detection of a faint stimulus requires a judgment- it is not an all-or-none process Detecting a stimulus requires making a judgment about its presence of absence, based on a subjective interpretation of ambiguous information Response Bias: refers to a participant’s tendency to report detecting the signal in an ambiguous trial o higher level processes in the brain, such as beliefs and expectancies, influence how sensations from the environment are perceived Sensory Adaptation A decrease in sensitivity to a constant level of stimulation Sensory systems tuned to detect environmental changes If a stimulus is presented continuously, the responses of the sensory systems that detect it tend to diminish over time When a continuous stimulus stops, the sensory systems respond strongly as well
What are the basic sensory processes? In Taste, Taste Buds Detect Chemicals Gustation: The sense of taste To keep poisons out of our digestive system while allowing food in Taste buds: Sensory receptors that transduce taste information - When food stimulates taste buds, they send signals to the brain, which then produces the experience of taste - Every taste experience is composed of a mixture of 5 basic qualities: sweet, sour, salty, bitter, and umami (“savory” or “yummy”) - The entire taste experience happens not only in the mouth, but also the brain, which integrates these various sensory signals - Supertasters: highly aware of flavours and textures and are more likely than others to feel pain when eating very spicy foods - Taste preferences come from our different numbers of taste receptors
-
Cultural influences also affect food preferences, and your mother’s preferences (passed on to offspring)
In smell, the nasal cavity gathers odorants Olfaction: The sense of smell, which occurs when receptors in the nose respond to chemicals - Has the most direct route to the brain - We smell when chemical particles or odorants pass into the nose and when we sniff into the nasal cavity’s upper and back portions - In the nose and nasal cavity, odorants come into contact with: Olfactory Epithelium: The thin layer of tissue, within the nasal cavity, that is embedded with smell receptors - These receptors transmit information to the: Olfactory Bulb: The brain centre for smell, located below the frontal lobes - From here, smell information goes direct to other brain areas - Smell signals bypass the thalamus In touch, sensors in the skin detect pressure, temperature, and pain Haptic sense: the sense of touch - Conveys sensations of temperature, of pressure, and of pain and a sense of where our limbs are in space - Anything that makes contact with our skin provides tactile stimulation which gives rise to an integrated experience of touch - Haptic receptors for both temperature (separate hot and cold receptors) and pressure are sensory neurons that terminate in the skin’s outer layer - The integration of various signals and higher level mental processes produces haptic experiences Two types of pain - Warning system that stops you from continuing activities that may harm you - Actual experience of pain is created by the brain - Most pain experiences result when damage to the skin activates haptic receptors - Two kinds of nerve fibres identified with pain: o fast fibres for sharp, immediate pain o slow fibres for chronic, dull, steady pain - Important distinction between the fibres is the myelination or nonmyelination of their axons, which travel from the pain receptors to the spinal cord - Fast acting receptors activated by strong physical pressure and temperature extremes, slow acting receptors are activated by chemical changes in tissue when skin is damaged
Gate control theory - Past experiences are extremely important in determining how much pain a person feels - Gate Control Theory of Pain: states that for us to experience pain, pain receptors must be activated and a neural “gate” in the spinal cord must allow the signals through to the brain o Pain signals transmitted by small-diameter nerve fibres, which can be blocked at the level of the spinal cord (prevented from reaching the brain), by firing of larger sensory nerve fibres - Sensory nerves fibres can “close a gate” and prevent or reduce the perception of pain - Worrying about or focusing on the painful stimulus, seem to open the pain gates wider - Division of perception of pain in the brain: o One area responds to the sensory input from the part of the body that is in pain- the full pain of a chronic backache, the stabbing pain of cut and so on o Other part of the brain that is involved when we feel pain registers the emotional aspects of pain, which includes how unpleasant it is - When we feel pain, both areas of the brain are activated In hearing, the ear detects sound waves Audition: The sense of sound perception - Second source of information to world (vision first) - Hearing results when the movements and vibrations of objects cause the displacement of air molecules - These molecules produce a change in air pressure, and that change travels through the air Sound Wave: the pattern of the changes in air pressure through time that results in the percept of a sound - The wave’s amplitude determines its loudness; higher amplitude is perceived as louder - The sensory experience of hearing occurs within the brain, as the brain integrates the different signals provide by various sound waves Eardrum (tympanic membrane): A thin membrane, which sound waves vibrate, that marks the beginning of the middle ear - Our ability to hear is based on the intricate interactions of various regions of the ear, which convert sound waves into brain activity, producing the sensation of meaningful sound - Changes in air pressure produce sound waves that arrive at the outer ear and travel down auditory canal to eardrum - Eardrum vibrations are transferred to ossicles (3 tiny bones called the hammer, anvil, and stirrup)
-
Ossicles transfer the eardrums vibrations to the oval window, a membrane of the cochlea, or inner ear (fluid filled tube that curs into snail like shape) Pressure waves are created I the inner ears fluid and these waves prompt the hair cells to bend and cause neurons on the basilar membrane to fire Hair cells are the primary auditory receptors The mechanical signal of a sound wave hitting the eardrum is converted into a neural signal that travels to the brain via the auditory nerve
Locating sounds - Sound reaches the ear that is closest to the sound first, the it reaches the second ear (indicating that the source is closer to the other ear) In vision, the eye detects light waves - Very little of what we see takes place in the eyes, rather what we see results from constructive processes that occur throughout much of the brain to produce our visual experiences Cornea: The clear outer covering of the eye (where light first passes through) - Focuses on incoming light in a process called refraction - Light rays then enter and are bent farther inward by the lens which focuses the light to for an image on the retina Retina: The thin inner surface of the back of the eyeball. The retina contains the photoreceptors that transduce light into neural signal Pupil: The small opening in the eye; it lets in light waves - Determines how much light enters the eye through either contracting or dilating Iris: The coloured muscular circle on the surface of the eye; it changes the shape to let in more or less light -
The lens and cornea work together to collect and focus light rays reflected from an object, to form on the retina an upside-down image of the object
Rods and Cones - The retina has two types of receptor cells; Rods: Retinal cells that respond to low levels of illumination and results in backand-white perception (night vision) Photo pigments: light sensitive chemicals that initiate the transduction of light waves into electrical neural impulses Cones: Retinal cells that respond to higher levels of illumination and result in colour perception
Fovea: The centre of the retina, where cones are densely packed Transmission from the eye to the brain - After light is transduced into neural impulses by rods and cones, other cells in the retina- bipolar, amacrine, and horizontal cells- perform on those impulses a series of computations that help the visual system process the incoming information - Ganglion cells: the first cells in the visual pathway to generate action potentials o send their signals along their axons from inside the eye to the thalamus o these axons gathered into a bundle, the optic nerve, which exits the eye at the back of the retina o blind spot: the point at which the optic nerve exits the retina has no rods or cones (in each eye) - ganglion cells lying within the visual areas of the thalamus are transmitted to the primary visual cortex The detection of visual information - Particular visual neurons respond best to particular colours, shape orientations, or directions of motion Receptive Field: The region of visual space to which neurons in the primary visual cortex are sensitive - Visual receptive fields can be thought of as being located on a specific region of the retina or a specific location in visual space Lateral inhibition Lateral Inhibition: A visual process in which adjacent photoreceptors tend to inhibit one another - Our visual systems are sensitive to edges because edges tell us where objects end The colour of light is determined by its wavelength - Not seeing colours, but seeing the light waves that objects reflect to our eyes - Visible light consist of electromagnetic waves and the colour of light is determined by the wavelengths of the electromagnetic waves that reach the eye - We categorize colour along 3 dimensions: hue, brightness, and saturation - Hue: consists of the distinctive characteristics that place a particular colour in the spectrum - Brightness: colour’s perceived intensity, or luminance, which is determined chiefly by the total amount of light reaching the eye o a psychological dimensions that has no simple physical correlate; lightness is determined by its brightness relative to its surroundings - Saturation: a colour’s purity, or intensity- the vividness of the hue
Subtractive Colour Mixing: a way to produce a given spectral pattern in which the mixture occurs within the stimulus itself and is actually a physical, not psychological process (eg. Mixing paints) Colour is determined by mixture of wavelengths from a stimulus Colour can be produced in 2 ways: o Subtractive and additive mixture of wavelengths When we see a blue shirt, it is blue because the material the shirt is made from has absorbed medium and long wavelengths (yellow and red) and is reflecting only short wavelengths that are perceived as blue Red, yellow and blue are the subtractive primary colours, mix all together and you get black because these pigments absorb nearly all colours of the visible spectrum Additive Colour Mixing: a way to produce a given spectral pattern in which different wavelengths of lights are mixed. The percept is determined by the interaction of these wavelengths with receptors in the eye and is a psychological process. (stage lighting) When lights of different wavelengths are mixed what you see is determined by the interaction of the wavelengths within the eye`s receptors Any colour can be created by combining all 3 wavelengths Red, green and blue are the additive primary colours /mix all together to get white light Explaining Colour Vision: Colour is a product of our visual system and does not exist in the physical world There are 3 different cones in the retina-each responds to a different wavelength o One type is sensitive to blue light (Short ww) o Sensitive to green light (Medium ww) o Remaining cones are sensitive to red light (Long ww) o We see yellow because it stimulates L/M cones equally while not stimulating S Our perception of colour is determined by the ratio of activity among the three types of cone receptors To account for some colours seeming “opposite” to each other we must look at ganglion cells (second stage of visual processing) Different combinations of cones converge on the ganglion cells One type of ganglion cell may receive excitatory input from L cones (red) but may be inhibited by M cones (green) o This creates the perception that red and green are opposite Simultaneous Contrast: optical illusion in which identical stimuli appear different when presented against different backgrounds. (we are unaware of factors affecting our perception)
Humans and Animals have other Sensory Systems Kinesthetic sense: perception of our limbs in space; helps us co-ordinate movement Vestibular Sense: perception of balance; from receptors in the ear (we get sea sick or car sick when the vestibular system and the visual system conflict each other). Some animals have sonar sense and electroreception.
The Evidence for Extrasensory Perception (ESP) is weak/non-existent
(6th sense) communicate with ghosts, predict future, read minds Through experiments there is very little support for ESP Need to come up with empirical evidence to prove it or disprove it
What are the Basic Perceptual Processes Perception Occurs in the Brain Fig 5.32 The thalamus relays all sensory information to the cortical and other areas of the brain. Primary sensory areas: Hearing: Primary auditory cortex(A1, for the first auditory area), which is in the temporal lobe, different areas of it respond to different frequencies (high/low) Touch: Primary somatosensory cortex (S1), which is in the parietal lobe, areas with greater sensitivity have larger regions of S1 dedicated to them (lips) Vision: study of perception has focused to a large extent the on the visual cortex (believed that half of the cerebral cortex participates in visual perception in some way). Primary visual cortex (V1) is located in the occipital lobe. Some neurons in V1 have higher firing rates when particular orientations of lines are put before them. (may fire more if it is straight then if it is tilted at an angle/known as simple cells) Fig 5.33 What vs where: 2 parallel pathways from the occipital lobe: o Ventral Stream (what): specialized for perception and recognition of objects (determining colours and shapes) o Dorsal Stream (where): spatial perception o One can be damaged while other one works (a lady could not identify a picture of an apple but when told to draw an apple she could through memory; this is known as object agnosia-inability to recognize objects)
Object Perception Requires Construction One of the most important roles for V1 (primary visual area in the brain) is to extract the edges and contours that define the boundaries of objects. One of the 1st steps in processing a from appears to be encoding the features that compose it.
Gestalt Principles of Perceptual Organization: Theory that states that perception is more than the result of accumulating sensory data. States that our brains use innate (built-in) principles to organize sensory information. Proximity and Similarity: Principle of Proximity states that the closer two figures are to each other, the more likely we are to group them and them as part of the same object, Principle of Similarity states that we tend to group figures according to how closely they resemble each other (shape/colour) The “Best” Forms: Good continuation is the tendency to interpret intersecting lines as continuous rather that changing direction. We complete objects that are blocked from our view by an occluder. Closure refers to the tendency to complete figures that have gaps Fig. 5.35 Figure and Ground: Most basic organizing principles is distinguishing between figure and ground Bottom-Up Processing: a hierarchical model of pattern recognition in which data are relayed from one processing level to the next always moving to a higher level of processing Top-Down Processing: a hierarchical model of pattern recognition in which information at higher levels of processing can influence lower, “earlier” levels in the processing hierarchy o Because of these 2 types of processing, context affects perception , what we expect to see influence what we perceive Fig 5.36 Face Perception: Several studies support the idea that the human face reveals “special” information that is not available in any other way (mood, attentiveness, race, age) Specific regions of the brain (fusiform gyrus and even as specific as neurons)are very responsive to anything that looks like a face. Prosopagnosia is deficit in the ability to recognize races (you can still recognize objects/showing that they differ) Facial recognition supports the idea that the mind is adaptive (perceives anger on a man quicker than it does on a women because they commit most violent crimes). Own sex bias, women are most accurate when recognizing woman faces. We have a very hard time recognizing faces when they are inverted. Biological, Individual (females recognize faces better than males), Social (anger on a man’s face) and Cultural (own race bias) impacts of face recognition are apparent. Regaining Vision by Fixing the Eyes: “people see with their brains not with their eyes”. With todays’ technology people who become blind are able to regain their sight. Those who are blind for many years have much more difficulty restoring their vision after operation (corneal and stem cell implants), things like face recognition and depth perception. The brain is fine-tuned through experience, if a cortical region is not used it ceases to develop normally.
Depth Perception Is Important For Locating Objects Binocular Depth Cues: Cues of depth perception that arise from the fact that people have two eyes
The brain applies the same rules to both 2D and 3D objects by rapidly and automatically exploits prior assumptions it has about the nature of the relationship between 2 dimensional and 3 dimensional objects (cues) Binocular Disparity: a cue of depth perception that is caused by the distance between a person’s eyes, which provides each eye with a slightly different image, the brain has access to two different but overlapping images Stereoscopic Vision: ability to determine an object’s depth based on that object’s perception to each eye 5.42 Monocular Depth Cues: cues of depth perception that are available to each eye alone A three-dimensional array of objects creates exactly the same image on the retina that a photograph of the same array of objects does. (watching movies) o Occlusion: a near object blocks an object that is further away o Relative Size: far-off objects project a smaller retinal image than close objects do o Familiar Size: we know how large familiar objects are, so we can tell how far away they are by the size of their retinal images o Linear Perspective: parallel lines appear to converge in the distance o Texture gradient: as a uniformly textured surface recedes, the texture continuously becomes denser o Position Relative to horizon: objects below the horizon that appear higher in the visual field are perceived as being away. Objects above the horizon that appear lower in the visual field are perceived as being further away
Culture Influences Perception Do we automatically use picture cues or do we learn how to use them? If you were not raised in a “carpentered world” you would not know parallel lines seem to converge in the distance and therefore your culture influences your perception Kids who went to school and lived in rural areas are able to recognize illusions (Mueller-Lyer) than those that don’t Motion Cues for Depth Perception: Motion Parallax: is the relative movements of objects that are at various distances from the observer o Near objects pass quicker and objects that are further away seem to pass slower
Size Perception Depends on Depth Perception The size of an object’s retinal image depends on that object’s distance from the observer. Optical illusions can arise when normal perceptual processes incorrectly represent the distance between the viewer and stimuli-depth cues fool us into seeing depth when its’ not there.
Ames Box: diagonally cut room, with angled windows and tiles to produce an illusion. When one child is in one corner and a child of equal size is in the other, one appears as a giant Fig 5.49 The Ponzo Illsuion: size/distance illusion, monocular depth cues make the 2D figure seem 3D Fig 5.50
Motion Perception Has Internal and External Cues We have neurons specialized for detecting movement. 3 phenomena that offer insight into how the visual system perceives motion: Motion After Affects (water fall effect): occur when you look at a moving image for a prolonged period of time and then kook at a stationary scene, you see the second object as moving in the opposite direction as the than the first object. o Neurons get fatigued and less sensitive after period of time, so if scene changes other motion detectors respond Compensatory Factors: How do u know whether an object is moving or whether, you or your eyes are moving? Brain calculates an object’s perceived movements by monitoring the movement of the eyes, and perhaps also of the head, as they track a moving object. o Image Moving System and Eye Moving System Fig 5.52 Stroboscopic Movement: a perceptual illusion that occurs when two or more slightly different images are presented in rapid succession.
Perceptual Consistencies are based on Ratio Relationships
Perceptual Consistency: people correctly perceive objects as constant in their shape, size, colour, and lightness, despite raw sensory data that could mislead perception. Illusions occur when the brain creates inaccurate representations of stimuli To perceive any of the 4 consistencies, we need to understand the relationship between it and at least one other factor o Size Consistency: we need to know how far away the object is from us o Shape Consistency: we need to know from what angle we are seeing the object o Colour Consistency: we need to compare the wavelengths of light reflected from the object with those reflected from its background o Lightness Consistency: we need to know how much light is being reflected from the object and from its background Perceptual system is tuned to detect changes from baseline conditions, not just respond to sensory inputs Brain has built in assumptions that we can’t control
