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University of Toronto Scarborough
Steve Joordens

Chapter 5 Sensory Processing Sensation – detection of simple properties of stimuli (brightness, colour, warmth, sweetness) Perception – detection of objects, locations, movements and backgrounds Transduction – sense organs convert energy from environmental events into neural activity, sense organs convert into neural firing Receptor Cells – release chemical transmitter substances that stimulate other neurons, altering the rate of firing - distinguish between 7.5 different colours – action potentials cannot be altered Anatomical Coding – brains has no direct information about physical energy, it uses anatomical coding: interpret location and type of sensory stimulus when nerve fibers are active – body surface coding is anatomical Temporal Coding – coding of information in terms of time – rate of firing at a faster/slower rate according to intensity of the stimulus, axon can communicate quantitative information to the brain Anatomical – location of stimulus Temporal – intensity of stimulus Ernst Weber – just noticeable differences Weight – factor 1 in 40, brightness of white light 1 in 60 Weber Fractions Gustav Fechner – used jnd to measure peoples sensations S.S Stevens – power function to relate physical intensity to magnitude of sensation S = KI^b K= mathematical constant I= intensity raised to power of b Signal Detection Theory – threshold Jnd – line between not perceiving and perceiving Difference Threshold – minimum detectable difference between two stimuli Absolute Threshold – minimum value of stimulus that can be detected from no stimulus at all (eg. Using a dark disc as sample stimulus measured an absolute threshold) By convention, the threshold is the point at which the participant detects the stimulus 50% of the time because neurons are never absolutely still, they fire every now and then If neurons happen to be quiet – likely to detect If neurons happen to be firing – less likely to detect, lost in “noise” Signal detection theory – takes account of random changes in the nervous system Hit + Correct negatives – correct responses Miss + False alarms – incorrect responses Assessing people’s sensitivity regardless of their response bias ROC (receiver operating characteristics) – indicates people’s ability to detect stimulus Vision – light consists of radiant energy that is similar to radio waves Electromagnetic energy travels at 298 000 km/second Distance between the waves of radiant energy is 3.4m Wavelength of visible light ranges from 380 – 760 nanometers Cornea – transparent tissue covering the front of the eye Sclera – tough outer layer of the eye – “white” of the eye Iris – pigmented muscle of the eye that controls the size of the pupil Space immediately behind the cornea is filled with aqueous humor (watery fluid) – nourishes cornea, fluid must circulate and be renewed (if aqueous humor is produced too quickly or if the passage that returns it to the blood becomes blocked, the pressure within the eye can increase and cause damage to vision – disorder known as glaucoma) Lens contains no blood vessels because it must remain transparent, change in lens shape to adjust for distance is called accommodation (change in thickness) Nearsighted – eyes too long – image focused in front of fovea – concave lens corrects nearsightedness Farsightedness – eyes too short – image focused behind fovea – convex lens corrects farsightedness Retina – lines the inner surface of the back of the eye, performs sensory functions of the eye, more than 130 million photoreceptors embedded (receptive cell for vision in the retina) Information from photoreceptors is transmitted to neurons that send axons toward the optic disc  this portion of the retina is blind (blind spot) (axons joins optic nerve and travels to the brain) Johannes Kepler – credited with the suggestion that the retina contained the receptive tissue of the eye Christoph Schneider – lens is simply a focusing device Retina has 3 principal layers, light passes successively through the ganglion cell layer (front), bipolar cell layer (middle) + photoreceptor layer (back) Bipolar cells – transmitter substance, the neurons in which they form sypnases Ganglion cells – neurons whose axons travel across the retina ant through the optic nerves Rod – photoreceptor that is very sensitive to light but cannot detect changes in hue Cone – photoreceptor that is responsible for acute daytime vision and for colour perception Fovea – small pit near the centre of the retina containing densely packed cones, responsible for the most acute and detailed vision (125 million rods, 6 million cones) Vitamin A – ingredient in transduction of energy of light into neural activity 4 kinds of photopigments (1 rod, 3 cones) Rhodopsin – pink photopigment of rods, lose their colours when split by action of light (Franz Boll) The brighter the light, the more bleached photopigment Dark Adaptation – rate of regeneration of rhodopsin falls behind the bleaching process Vergence Movement – cooperative movement that keeps both eyes fixed on the same target (Depth Perception) falls on identical portions of the retina Saccadic Movement – rapid movement of eyes scanning a visual scene as opposed to smooth movements – McCollough Effect Pursuit movement – eyes maintain an imagine of a moving image upon the fovea Wavelength (hue) – perceptual dimension of colour Intensity (brightness) Purity (Saturation) Synthetic Sensory Modality – puts together rather than analyze wavelengths of lights (Vision) Auditory – analytical, hear both high and low notes Mix paints – subtracting colour – darker result Mix wavelengths – adding colour – brighter result Trichromatic Theory (Thomas Young) – eye contains three types of colour receptor, each sensitive to a different hue that brain synthesizes colour by combining information from each receptor “Pure” Colours: blue, green, red – Helmholtz 3 types of photopigments – 420, 530, 560 nm More red and green cones, far fewer blue cones Opponent Process – representation of colours by the rate of firing of 2 types of neurons: red/green, yellow/blue – cannot see yellow/blue, red/green because the axon that signals red or green and yellow or blue can either increase or decrease its firing, cannot do both Negative afterimages – cause: adaptation to the rate of firing of retinal ganglion cells – when they are excited or inhibited for a long period of time, show rebound effect Protanopia – hereditary anomalous colour vision caused by defective red cones in the retina nd 2 colour defect Deuternopia – caused by defective green cones in the retina 1 in 20 males have some sort of colour blindness because they only have one x chromosome 3 colour defect Tritanopia – caused by lack of blue cones in the retina Audition – Hz (hertz) can hear from 30 – 20000 Hz Timbre – complexity of sound vibration Ear – pinna helps funnel sound through the ear canal Ear drum (tympanic membrane) attached to ossicles (little bones) 3: hammer (malleus), anvil (incus), stirrup (stapes) - bone act together in lever fashion to transmit vibrations of the ear drum to receptive organ (cochlea – snail – accurate shape, where auditory transduction takes place) Oval window – transmits sound vibration into the fluid within the cochlea Basiliar membrane – one of two membranes that divide the cochlea of the inner ear into 3 compartments, receptive organ for audition resides here Different frequencies in sounds cause different parts of the basilar membrane to vibrate High frequency sounds cause the end near the oval window to vibrate, low frequency sounds cause the tip to vibrate Auditory Hair cell – sensory neuron of auditory system, located on basiliar membrane Cilium – hair like, involved in movement/ or in transducing sensory information, found on receptors in the auditory and vestibular systems Tectorial membrane – shelf against which the cilia of auditory hair moves, axons cannot fire over 1000 times per second Kiang – recorded electrical activity of single axons in auditory nerve Harmonic – over tone, component of a complex tone Fundamental frequency – lowest, usually most intense frequency of a complex sound “sounds basic pitch” Timbre – perceptual dimension of sound Patter recognition – identifying particular sound sources Locating Source of Sound – relative loudness and difference in arrival time Superior Olive – initial processing of sound MLD (masking level difference) – noise is better heard if it goes into two ears instead of one 1. Pressure waves in ear drum  ossicles (little bones) vibration of stirrup behind oval window create pressure changes in the fluid within the cochlea, causing basilar membrane to vibrate back and forth  causes hair cells on basilar membrane to move to textorial membrane  resulting pull of cilia of the hair cells stimulates them to secrete a transmitter substance that excites neurons of the auditory nerve  informs brain of presence of sound Olfaction – sense of smell Pheromones – chemical signals, usually detected by smell or taste that regulate reproductive and social behaviours between animals Papilla – small bump on tongue that contains groups of taste buds – a group of gustatory receptor cells Chemosense – one of the two sense modalities (gustation & olfaction that detect presence of particular molecules present in the environment) Umami (good taste) refers to taste of monosodium glutamate. Sodium depolarizes the cell, causing it to release neurotransmitters, if body’s sodium falls, we cannot retain water, blood volume will fall, can result in heart failure Women have better sense of smell than men, two olfactory system Dogs have more sensory receptors Olfactory mucosa – contains cilia, olfactory receptors st Olfactory bulbs – stalk like structures, contain neural circuits that perform 1 analysis of olfactory info Body senses – Somatosenses – touch, pain, temperature Free Nerve Ending – dendrite of somatosensory neuron Pacinian Corpuscle – specialized somatosensory nerve ending that detects mechanical stimuli, especially vibrations Entire surface of the human body is innervated (supplied with nerve dibers) Most sensitive regions: lips and fingertips Two point discrimination method – minimum distance between two small points that can be detected as separate stimuli when pressed against a particular region of the skin Phantom limb – sensations that appear to originate in a limb that has been amputated, inherent in the organization of the parietal cortex Muscle spindles – inform brain on change in muscle length – stretch receptor Vestibular apparatus – receptive organs of the inner ear that contribute to balance and perception of head movement Semicircular canal – one of three organs in the inner ear that respond to rotational movements of the head Vestibular sacs – one of two receptor oragans in each inner ear that detect changes in tilt of head – contain crystals of Calcium Carbonate – we have at least 6 thermometers Chapter 6 Module – block of cortical tissue that receives information from the same group of receptive cells Receptive field – the portion of the visual field in which the representation of stimuli will produce an alteration in the firing rate of a particular neuron Ventral stream – flow of information from the primary visual cortex to visual association in the lower temporal lobe, used to form the perception of the object’s shape, colour, and orientation “what” system Doral stream – flow of information from the primary visual cortex to visual association area in the parietal lobe, used to form the perception of an object’s location in the dimensional space “where” system and it its moving Recognition of visual patterns + identification of particular objects take place in the inferior temporal cortex Visual Agnosia – inability to identify object Prosopagnosia – difficulty recognizing people’s faces, caused by damage to visual association cortex FFA (Fusifam Face Area) – region of ventral stream of the visual system that contains face recognizing circuits Akinetospia – inability to see motion Cerebral Achromatopsia – inability to discriminate different hues Retina  Thalamus  Primary visual cortex “module” tiles Extrastriate body area (EBA) – region of occipital lobe, responds to forms resembling human body – activated by photographs PPA (Parahippocampal place area) – region of visual stream, below the hippocampus that is activated by visual scenes – able to recognize both natural and human made scenes but unable to identify objects belonging to these scenes Perception of spatial information – parietal lobe receives visual, auditory, somatosensory Perception  damage disrupts perceiving and remembering the location of objects/controlling the movement of the eyes and limbs Doral stream located in posterior parietal cortex  involved in visual attention and control of eye movements, hand movement, perception of depth Perception of movement – extrastriate cortex Perceiving three dimensional forms – form from motion – superior temporal sulcus Figure – visual stimulus – self contained object Ground – formless background against objects seen Gesalt laws of organization Proximity – elements located closest to each other are perceived as belonging to the same figure Similarity – similar elements are perceived as belonging to the same figure Good continuation – given two or more interpretations of elements that form the outline of the figure, the simplest interpretation will be preferred Closure – elements missing from the outline of a figure are filled in by the visual system Common fate – elements that move together give rise to the perception of a particular figure Models of patter perception Templates – in the nervous system and is used to perceive objects or shapes by a process of comparison “cookie cutter” exact matches Prototypes – resemble templates but are much more flexible, does not look for exact matches, accepts a degree of disparity Distinctive features – physical characteristic that helps distinguish it from other objects Role of context Bottom up processing – perception based on successive analyses of the details of the stimuli that are present Top down processing – perception based on information provided by the context in which the stimulus is encountered Eg. Memory about kitchen specific features  then  loaf of bread Whorf hypothesis – language can strongly affect how we perceive the world Linear perspective – monocular cue of perspective (depth) drawing of images on flat surfaces such that parallel lines receding from the viewer are seen to converge at a point on the horizon Texture – fineness of detail present in the surfaces of object or in the ground or floor of scene Coarser texture looks closer Finer texture looks farther away Haze – monocular cue of depth perception – objects that are less distinct in their outline and texture are seen farther away from the viewer Shading – monocular cue of depth perception – determines whether portions of the surfaces of an object are perceived as concave or convex – which part is closer, farther Elevation – objects nearer the horizon are seen as farther from the viewer Motion parallax – monocular cue of depth perception, as we pass by a scene, objects closer to us pass in front of objects father away – allows us to make inferences about relative points Perceptual constancy – mechanism that maintains a perceptual judgment as external stimulus changes Perception of motion – one of the most primitive aspects of visual perception Pigeon’s visual system contains three distinct classes of neurons that separately carry information about looming objects “early warning” of impending collision D
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