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Matthias Niemeier

Lecture 1: Introduction Early Philosophy  Plato o Nativism: our perceptions are not derived from external sources (senses). We have innate abilities o Perception depends on events and energy that change in the world o Our understanding of reality is restricted to what we can perceive  Heraclitus o We can never perceive the exact same thing more than once in the world b/c the first time we experience it changes how we experience it the second time; everything flows  Adaptation: when we get used to something b/c it’s been there for a while  Democritus: we sense things b/c atoms from objects bounce off to interact with atoms in our organs. Perception is the physical interaction b/w the world and our bodies. Primary and secondary  Sensory transducer: a receptor that changes physical signals form the environment into neural signals that the brain can interpret (for every sense )  Hobbes: everything we know and imagine is learned through senses; only matter exists  Locke: our thoughts are all derived from the experiences we have with our senses  Fechner: known as the “father of experimental psychology” o Psychophysics: mix of the mind (psychological) and matter (physical) o Panpsychism: all matter has consciousness even inanimate things  Weber o JND: the minimum change it takes a person to perceive the difference b/w one stimulus and a reference stimulus  Two-point threshold (Fechner): the smallest distance at which two stimuli can be distinguished  Descartes o Dualist view: there is a body but a mind exists as well; didn’t trust senses o Mind-body dualism: the idea that two distinct principles exist: the mind and body  Monism: the idea that humans are only made of one thing: the body or the mind o Materialism: only body/matter/senses exists o Mentalism: only the mind exist  Empiricism: the idea that everything is learned from the senses  Fechner’s Law: as intensity of stimulus magnitude increases, sensation magnitude increases  Absolute threshold: minimum amount of stimulation necessary for person to detect a stimulus Psychophysical Methods o Method of constant stimuli: presentation of stimuli until person can detect the smallest intensity; simple but inefficient b/c stimuli may be well above or below threshold o Method of limits: taking the crossover points of what person can hear and what they can’t hear o Method of adjustment: not used to measure threshold o Magnitude estimation: person rates the sound on a scale o Cross-modality matching: matching the intensities of two different modalities Signal Detection Theory: a psychophysical theory that quantifies the response of an observer to the presentation of a signal in the presence of noise Lecture 2: The First Steps in Vision A Little Light Physics  Light: a wave (when it moves around the world); a stream of photons(when it is absorbed), tiny particles that each consist of one quantum of energy o Absorbed: when energy is taken up by a surface (darker) o Diffracted: when energy is bent or having waves that are spread out (sun thru trees) o Reflected: when energy is redirected as it hits a surface (4 parts of eyes reflect light) o Transmitted: when energy passes thru a surface when it is not absorbed or reflected o Refracted: when a medium alters energy as it passes thru another medium (light entering water from air) The Human Eye  Evolution of the eye o Region of photosensitive cells: every single photoreceptor gets light on same side of body; everything is completely blurred o Depressed/folded area: light can only come from certain directions; still blurred o Pinhole: finer directional sensitivity but limited imaging; not very hygienic o Transparent humor develops o Distinct lens develops o Iris and separate cornea develop  Parts o Cornea: no blood/vessels; blink reflex (tears); transparent sensory nerve endings; light photons are usually transmitted thru it o Pupil: controls amount of light reaching retina; hole in the iris o Aqueous humor: water in anterior; behind cornea; gives O2 and nutrients, remves waste o Vitreous humor: water in posterior o Lens: no blood; transparent o Retina: contains photoreceptors; sends image to optic nerve o Light passes thru cornealensretina o Fundus: back surface of the eye; seen with ophthalmoscope o Optic disc: where veins, arteries, blood vessels enters the eye and axons leave the eye  Accommodation: ciliary muscles makes lens fatter (more refraction) to see closer objects and thinner (less refraction) to see farther away objects Problems with the Eye  Myopia: near-sightedness, concave lens, negative, image in front of retina, longer eyeball  Hyperopia: far-sightedness, condense lens, positive, image behind retina, shorter eyeball  Emmetropia: perfect match of refractive power and length of eyeball The Retina  5 major classes of neurons: photoreceptors, ganglion cells, horizontal cells, bipolar cells and amacrine cells  In order for light to pass thru photoreceptors, it must pass thru all these cells and layers  Photoreceptors: o Cells in retina that initially transduce light energy into neural energy o made up of rods (90 million, smaller) and cones (4-5 million, larger)  Rods and Cones o Rods are for night-scotopic; cones are for day-phtotopic,fine visual acuity and color o Visual pigments are made of two parts  Chromophore: captures photons  Opsin: absorbs light of a specific wavelength o Two types of visual pigment  Rhodopsin: for rods  3 types for cones: S-cones (shorter, blue, 5-10 %, not in center of fovea), M-cones (medium, greenish), and L-cones (twice as many as M-cones, long, red/yellow Retinal Information Processing  Capturing a photon: when light hits a photoreceptor, photoactivation begins o Hyperpolarization: sodium channels close, when they are stimulated  Increase in negativity, decrease in positivity o Graded potentials  Lateral pathway: horizontal and amacrine cells  Vertical pathway: photoreceptors, bipolar and ganglion cells o Bipolar cellssynapse with either rods or cones and with horizontal cells and thenpass signals onto ganglion cells o Ganglion cellsreceive input from bipolar and amacrine cells and thensend messages off to the brain thru their axons  Bipolar cells o Diffuse: info from rods and cones onto a single bipolar cell; blurred vision, lose lot of detail, less acute vision, but more sensitive o Midget: info from single cone; high acute vision, less sensitive o ON bipolar cells: respond to an increase in light o OFF bipolar cells: respond to a decrease in light  Ganglion cells o P: gets signals from midget, small, but more (70%), shape perception o M: gets signals from diffuse, large, but less (8-10%), motion perception o ON: depolarizes in response to increase in light intensity in its receptive field center o OFF: depolarizes in response to decrease in light intensity in its receptive field center  Mechanisms for dark and light adaptation: pupil dilation, photoreceptors, and photopigment replacement  Retinitis pigmentosa: progressive death of photoreceptors and degeneration of epithelium Lecture 3: Spatial Vision Gratings  3 Types of Gratings o Rectangular grating: very abrupt changes b/w dark and light o Sine wave grating (sinusoidal): light stripes are perfectly white and dark stripes are perfectly black o Gabor: sine wave viewed through a circular aperture defined by a 2D Gaussian  3 characteristics of gratings: o Frequency:  cycles/s= Hz; a cycle is one repetition of a black and white stripe  cycles/visual degree=cpd; o Amplitude o Phase: the position of a grating  Why gratings are important o Patterns of stripes with fuzzy boundaries are quite common o The edge of any object produces a single stripe, often blurred by a shadow, in the retinal image o Important cues for visual recognition: we first decompose something in order to recognize it o Efficient coding  Fourier Transform: an operation that breaks down a function/image into sine waves of different frequencies  Frequency components of an Image o Images can b
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