Chapter 5 Sensation and Perception PDF

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PSY 1101 — Chapter 5: Sensation and Perception 5.1 Foundations of Perception

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Brain is isolated from the rest of the body Sensory education begins before birth Sensations: The elementary parts of the environment that the brain uses to create meaning. Perception: The processing of stimuli to create a sensory understanding of the world.

Top-Down and Bottom-Up Processing

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Brain uses prior understanding to make a “guess”, when that guess makes sense, you use memory to apply it to future problems Bottom-up processing: The processing of physical messages delivered to the senses. Top-down processing: The integration of a person's beliefs, memories, and expectations into their sensory experiences to create a perception.

The Principles of Gestalt

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Figure-ground: certain information is given priority over the background Principle of proximity: objects that are close to one another will be grouped together Principle of similarity: objects that are physically similar to one another will be grouped together Principle of closure: people tend to perceive whole objects even when part of that information is missing. Principle of good continuation: if lines cross each other or are interrupted, people tend to still see continuously flowing lines Principle of common fate: objects that are moving together will be grouped together.

5.2 Vision The Eye

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20% of the cortex plays a role in the interpretation of visual information Light is a form of electromagnetic radiation W are only able to see around 400-700 nanometers of light The eye actively adjusts its behaviour to maximize the quality of light that reaches the sensory cells in your retina Retina: the thin layer of tissue on the back of each eye that contains the photo sensitive receptor cells Cornea: the transparent covering of the eye; performs about 80% of the focusing of a visual image Pupil: the hole in the centre of your eye that allows light to enter. Iris: the ring of pigmented tissue surrounding the pupil. Responsible for controlling the diameter and size of the pupil, thereby controlling the amount of light that reaches the retina. Lens: a flexible piece of tissue, located behind the pupil that focuses light on the retina. Accommodation: the process through which the lens changes shape to bring objects into focus on the retina. Cornea —> pupil —> lens —> retina —> rods and cones Nearsighted = lenses that bring light into focus before reaching the retina Anterior chamber/aqueous humour: liquid-filled space between the cornea and iris, This fluid is routinely cleaned from the eye but blockage can result in built-up pressure on the eye, and the development of glaucoma. Choroid: Highly vascularized portion of the eye that delivers nutrients to the photoreceptor cells of the retina. Optic Nerve: translates information from the retina and sends that information to the visual cortex. The area that the optic nerve occupies on the retina leaves a blind spot for our vision.

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Fovea: portion of the retina directly behind the pupil. It contains a large concentration of cones and no rod. Sclera: the relatively tough, white portion of the eye. This area is vascularized and surround the cornea. The image depicts a sclera with dilated blood vessels, leading to a reddish appearance. Photoreceptors/photosensitive cells: specifically sensitive to exposure to light Rods: one kind of photoreceptor in the retina; it typically is most responsive to low levels of light Cones: a type of photoreceptor in the retina that is typically most receptive to bright lighting conditions and is responsible for communicating information about acuity and colour. The back of each retina contains approx 126 million photoreceptors Visual acuity: transmitting of fine detail information Dark adaptation occurs in 2 stages: ● (1) cones rapidly respond to the change in light — after about 8 mins the cones cannot become any more sensitive ● (2) the rods will increase in sensitivity for about 20 mins cones communicate information about wavelength (perceived as colour) Light first strikes the cornea, which protects the outer layer of the eye. It then enters the interior of the eye through the pupil, which is an opening between the outer and inner eye. Next the lens focuses light onto the retina, which is composed of rod and cone cells. The iris is the portion of the eye that gives your eye its colour (and regulates the amount of light that can enter the eye)] Nocturnal animals are likely to have a large number of rods to detect as much light as possible

The Retina

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Bipolar cells add together the firing of several photoreceptors and send a different kind of message to a ganglion cell Diffuse bipolar cells: Part of the bipolar layer of the retina. These cells receive signals from the rods and send their messages to large (magno) ganglion cells. Midget bipolar cells: Part of the bipolar layer of the retina. These cells receive signals from cones and send their messages to the small (parvo) ganglion cells. Messages leave the eye and enter the brain via the optic nerve Blind spot is the place where the axons of the ganglion cells leave the eye

The Visual Cortex

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Optic Chiasm: An X-shaped structure where the optic nerves from each eye cross before the message is sent to the thalamus. Information from the right side of both eyes is sent to the left hemisphere, information on the left side of the retina in both eyes is sent to the right side of the brain. Lateral geniculate nucleus (LGN): the 6-layer portion of the thalamus that processes and organizes visual information. Visual striate cortex: the location in the occipital lobe where visual information is organized and analyzed. We have over 30 areas in the back of the brain dedicated to analyzing and organizing visual information. Retinotopic organization: the spatial organization of the retinal image is maintained through the visual pathway. Feature detectors: specialized cells in the visual cortex that respond most actively to specific stimuli. Simple cell: feature-detecting cells in the visual striate cortex that respond to lines of specific orientations. Complex cells: cells in the visual striate cortex that respond to lines of specific orientations in motion. Ventral stream: Also known as the “What stream”, this pathway takes information from the occipital lobe to the temporal lobe where we are able to identify an object. Dorsal stream: Also known as the “where stream”, this pathway takes information from he occipital lobe to the parietal lobe, where we are able to identify object location Visual information also travels to the limbic system Light travels from: ● Cornea —> pupil —> lens —> rods/cones —> diffuse and midget bipolar cells —> m-cells and p-cells —> optic chiasm —> lateral geniculate nucleus of the thalamus —> visual cortex

Colour Vision

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Colour is the reception of wavelength Wavelength: the physical distance from one energy cycle to the next; changes in wavelength are often perceived as changes in colour Longer wavelengths: red (670nm) Medium wavelengths: greens (530 nm) Shorter wavelengths: blues (450 nm) White light: equal representation of all wavelengths Our brain uses information to create colours; colour allows us to derive information that is useful Short cones (s-cones): Cones in the visual system that respond maximally to short wavelengths Medium wavelength cones (m-cones): Cones in the visual system that respond maximally to medium wavelengths Long wavelength cones (l-cones): Cones in the visual system that respond maximally to long wavelengths Trichromatic theory: proposes that colour information is identified by comparing the activation of different cones in the retina. ● Explains colour blindness

The Opponent Process of Colour Vision

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Trichromatic theory has difficulty explaining how people perceive yellow P-cells will respond vigorously to one wavelength and reduce their firing if they receive a signal indicating a different one Opponent process: a theory of colour vision that suggests that cells in the visual pathway increase their activation when receiving information from one kind of cone and decrease their activation when they see a second colour. Colour constancy — seeing the same colour despite surrounding lighting conditions — can significantly fool us then multiple lighting conditions are presented at once According to Beau Lotto, colour enables us to see light in the same way a bat perceived texture through sound

Perceiving Depth

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The brain uses both bottom-up and top-down processing to understand what the retinal image is communicating about depth. Monocular depth cues: also known as pictoral cues, these depth cues only require one eye to understand messages of depth. Binocular depth cues: these cues require comparing an image as it falls on both eyes in order to understand how far away an object is from the viewer.

Monocular Depth Cues

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Occlusion occurs when one image partially blocks the view of a second object Relative height: objects closer to the horizon will appear farther away, and the greater distance between the object and the horizon, the closer the object will appear Relative size: when two objects are of equal size, the one that is farther away will take up a smaller portion of the retina. Perspective convergence: as parallel lines move away from us into the distance , they seem to converge or come closer together Familiar size: judging distances based on our knowledge of the objects size Atmospheric perspective: when more distant objects appear hazy and often have a slight blue tint

Binocular Depth Cues

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Because your eyes are in slightly different locations on your head, each retina has a slightly different image of the world Retinal disparity: the difference between retinal image that falls on both eyes. The brain uses disparity to calculate the distance between an individual and an object. The brain also uses the degree to which the eyes must turn inward to focus on an object to process depth information.

5.3 Hearing and Sound

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The first mammals lived underground in the dark, so vocalizations served as the primary means of communication between mother and offspring Animals that do not use light rely heavily on sound The physical message of sound is a form of energy that travels in a wave Sound is a mechanical energy and requires a medium like air or water to move through space Exposure to loud sounds will damage hearing Frequency: the physical measurement of a pitch or how high/low a sound is (measures in Hz) ● People can hear between 20 and 20000 Hz but best between 1000 and 5000 (range of speech) Intensity: The physical measurement of the loudness of sound. Measured in decibels (dB) Increased intensity causes the amplitude of the wave to increase

When Sound Enters the Ear

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Pinna: the external part of the ear Tympanic membrane (eardrum): transfers energy to the three smallest bones of the body known as the ossicles. Ossicles: Three smallest bones in the body. Responsible for amplifying vibrations arriving at the eardrum and transmitting these signals to the oval window of the cochlea. ● Consist of the malleus, the incus, and the stapes Cochlea: snail-shaped structure in the inner ear where the auditory hair cells are located, Basilar membrane: the tissue inside the cochlea where the hair cells are located. Transduction: process by which external sensations are converted into neural firing in the brain. Occurs when the vibrations against the oval window cause fluid inside the cochlea to move. Hair cells: the sensory neurons inside the inner ear that convert sound into neural firing. Sounds from many sources, complexities, amplitudes, and frequencies all arrive at the ear at the same time The brain uses qualities of the sound to infer meaning Place theory: the theory of audition that suggests we understand pitch because of the location of firing on the basilar membrane. Hair cells do not operate independently. Frequency theory: the theory of audition that suggests we understand pitch because of the rate of cellular firing on the basilar membrane.

The Auditory Cortex

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Auditory cortex: location in the temporal lobe where auditory information is processed. Medial Geniculate Nucleus: the portion of the thalamus that evaluates and organizes auditory information before sending it to the auditory cortex.

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Tonotopic organization: the spatial organization of the basilar membrane is maintained through the auditory pathway. The auditory system has cells with particularly rapid action potentials and abnormally large terminal buttons to help relay temporal components of the message. The organization is hierarchical

Sound Localization

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Many animals including humans use sound as a reliable cue for the location of objects. Binaural cues: auditory cues that require comparisons from both ears to understand an object’s location ● Interaural time differences: comparisons made between the small differences in arrival time of a sound in each ear ● Interauraul level differences: the brain compares intensity differences of sound as it arrives at each ear in order to understand object location

5.4 The Chemical Senses

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Chemoreceptors: sensory cells in the nose that respond to air molecules that we interpret as smell and taste. Smell and taste are the only senses that require you to ingest the physical stimuli in order to analyze the incoming information.

Smell

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Smell is the only sense that does not first go through the thalamus Plays a powerful role in our behaviour We have an adaptive response to evaluate food using smell and an overwhelming emotional response that accompanies it. Odourants: a stimulus that produces smells that can be perceived by the nose. Bears have an olfactory bulb around five times larger than ours Many animals have a superior sense of smell to humans

The Chemical Process of Smell

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Airborne molecules interact with receptor sites in the mouth and nose and are drawn into the upper nasal cavity Olfactory mucosa: the tissue that contains the chemoreceptors of the nose. Olfactory receptor neurons (ORN): neurons that are specifically responsive to odourants. Located in the olfactory mucosa People have around 350 olfactory receptor types each responding to specific ranges of molecules We can identify about 1 trillion different odours The ORNs send their signals to glomeruli in the olfactory bulb Some molecules with similar structures create different perceptions of smell and molecules with different structures can be interpreted as similar Smell is highly dependant on expectation

Taste

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Smell and taste are sometimes referred to as “gatekeepers” Taste relies on the correlation between the molecular properties of a substance and the effect of that substance on the body 5 basic tastes: sweet, salty, sour, bitter, and umami (savoury) Papillae: the little bumps on the surface of the tongue where tastebuds are located ● Filiform papillae: found all over the surface of the tongue and give it the “fuzzy” appearance — do not contain tastebuds ● Fungiform papillae ● Foliate papillae ● Circumvallate papillae Each taste bud contains 50-100 taste-sensitive cells Taste pore: the location of taste-sensitive cells on the tongue Afferent nerve: nerves leaving the tongue carry taste information to sensory processing areas of the brain. Eventually the information is processed in the OFC. Orbitofrontal cortex: the region of the brain that analyzes both taste and smell ● Contains bimodal neurons (neurons that respond to more than one sense) ● Location of flavour perception

5.5 Skin and Body Senses

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The skin is the largest organ in the body Skin helps with thermoregulation and protects us from the environment Serves as a source of information about the surface qualities of objects The physical message of touch is pressure Somatosensory cortex: the location in the parietal lobe where touch and motion are processed Mechanoreceptors: receptors in the skin that sense different kinds of pressure. The Merkel receptor and the Meissner corpuscle are located close to the surface of the skin and respond to pressure that is applied and then removed. High concentration fo Merkel receptors in the skin Ruffini cylinder is associated with interpreting the stretching of the skin Pacinian corpuscle feels vibration and texture Somatotopic organization: the spatial organization of touch; two adjacent points on your skin are represented by adjacent points on the somatosensory cortex. Sensory homunculus: a visual depiction of what our bodies would look like if they were built in proportion to their representation on the cortex. Our perception of an object depends not only on what we feel but also what we expect to feel

Temperature

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Temperature perception is in many ways a relative perception Our perception of temperature is dependant on what we are comparing the current stimulus to Thermoreceptors: receptors in the skin specifically designed to detect changes in temperature. ● Fire in response to chemical stimuli

Pain

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pain is an adaptive response to tissue damage Nociceptors detect pain and send a signal to our brains Pain is highly subjective and therefore more difficult to study Highly dependant on a person’s expectation and enculturation

Gate-Control Theory of Pain

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Gate-control theory of pain: a theory of pain perception that suggests that painful stimuli can be blocked in the spinal cord when you are engaged in other activities The brain prioritizes mobility over responding to the source of the pain Suggests that input happens along three pathways: ● (1) small diameter fibres (s-fibers): fire to damaging and painful stimuli. When s-fibers are activated, a (2) transmission cell (t-cell) becomes activated . The intensity of the perception of pain in part depends on the excitation of the t-cell. The third part of the model are (3) large diameter fibres (l-fibers) which send signals to the brain about stimulation that is not painful. L-fibres inhibit the activation fo t-cells when activated. ● Gate control theory cannot explain some aspects of chronic pain

The Subjective Nature of Pain

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The experience of pain depends not only on the sensations from the world but also what we expect to experience Pain is particularly susceptible to the placebo effect

Life without Pain?

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There are people who are unable to experience pain Congenital insensitivity to pain has two features: (1) the inability to perceive pain and (2) the inability to perceive temperature Results from a recessive allele on chromosome 2

5.6 The Kinaesthetic And Vestibular Senses The Kinaesthetic Sense

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Kinaesthetic sense: our sense of where our bodies are in space and how to move the body to accomplish specific tasks Relies heavily on our sense of touch but involves other receptors Information from receptors is sent to the somatosensory cortex

The Vestibular Sense

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Vestibular sense: sense of balance Sensory cells of the vestibular system are located in the cochlea Semicircular canals: the structures in the inner ear that sense changes in acceleratio...