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Chapter 4

Chapter 4 Psychology Notes.docx

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PSYC 1010
Agnieszka Kopinska

Chapter 4 Psychology Notes Weighting the Differences: The JND  JND is the smallest difference in the amount of stimulation a specific sense can detect  Related to absolute threshold because it is JND from nothing  Weber’s law: the size of JND is proportional to size of stimulus; as stimuli increases, the JND becomes larger Psychophysical Scaling  Fechner uses JND to measure sensory experiences  Fechner’s law: the size of sensory experience is proportional to number of JNDs the stimulus causes the experience above absolute threshold  Eg. going in a dark room turning on a light one by one  As stimulus intensity (amount of light) increases, sensation differences decreases (perceived brightness) Signal-Detection Theory  Signal detection theory: detection of stimuli involves decision processes and sensory processes influenced by variety of factors besides stimulus intensity  Eg.reporting enemy aircraft; there are four possible outcomes such as hits, misses, false alarms and correct rejections Retina  Retina: neural tissue in the inside back surface of the eye; it absorbs light, inputs images and sends visual information to the brain  Consists of layers of specialized cells  Optic disk- a hole in the retina where the optic nerve fibres exit the eye (aka, the blindspot) Visual Receptors:Rods and Cones  Receptors are in the inner layer of the retina  Cones are visual receptors that play a role in daylight vision and colour vision  b/c cones don’t respond to dim light, this explains why we can’t see in low illumination  fovea is a tiny spot in the centre of the retina containing only cones; visual sharpness is greatest at this spot  when you want to see something sharply, you move your eyes to focus the object in the fovea  Rods play a role in night vision and peripheral vision  Rods can handle the lion’s share of peripheral vision because they outnumber cones in the periphery of the retina  Eg.astronomers study dim light objects through eyepiece of the telescope Dark and Light Adaptation  dark adaptation: eyes are more sensitive to light in low illumination  declining absolute thresholds over time indicate you require less light to see  dark adaptation is complete in 30 minutes  light adaptation: eyes become less sensitive to light in high illumination  light adaptation improves visual sharpness under the prevailing circumstances Information Processing in the Retina  light strikes retina receptors, triggers neural signals to pass to a network of cells into the retina to send impulses along the optic nerve-collection of axons that connect the eye to the brain  axons carry visual info in a form of neural impulses to the brain  receptive field of a visual cell is the retinal area that when stimulated affects the firing of the cell  in receptive fields, light falling in centre has opposite effect of light falling in the surrounding area  when receptive fields are stimulated, retinal cells send signals toward the brain and sideways toward visual cells  lateral antagonism: when neural activity in a cell opposes activity in surrounding cells  “ “ is responsible for opposite effects that occur when light falls on inner vs outer portions of centre-surround receptive fields  l.a allows retina to compare the light falling in a specific area against general lighting Visual Pathways to the Brain  optic chiasm-point which optic nerves from the inside half of each eye cross over and then project to the opposite half of the brain  axons from the left half of each retina carry signals to the left side of the brain and axons from the right half of each retina carry information to the right side of the brain  main pathway projects into thalamus; 90% of axons from retina’s synapse in lateral geniculate nucleus (LGN)  visual signals are processes in LGN then distribute to areas in occipital lobe that make up primary visual cortex  second pathway leaves optic chiasm branching to a part of a midbrain called superior colliculus before travelling through the thalamus and onto the occipital lobe  parallel processing-occurs in magnocellular and parvocellular channels that remove different kinds of information from the same input  cells in the visual cortex are characterized as feature detectors, neurons respond to specific features of more complex stimuli  visual agonsia-inability to recognize objects  prosopagnosia-inability to recognize familiar faces  neurons in ventral stream pathway that are involved in remembering faces can learn from experience  eg.in a study participants were given extensive training in discriminating among artificial objects called Greebles  neurons that serve as face detectors were retuned to be responsive to other visual forms Multiple Methods in Vision Research  individuals suffering brain damage are observed when they do visual performances such as drawing  this is called McCollough effect  individuals with visual agnosia can’t perceive line (contour) orientation Summary Key Points  Light varies in wavelength, amplitude and purity. Light enters the cornea and pupil and focused upside down on the retina and lens. Distant objects appear blurry to nearsighted people and close objects appear blurry to farsighted people.  Retina is neural tissue in the eye that absorbs light, processes images and sends visual signals to the brain  Dark and Light Adaptation involve changes in retina’s sensitivity to light allowing the eye to adapt to changes in illumination  Retina transforms light into neural impulses that are sent to the brain through the optic nerve. Receptive fields are areas in the retina that affect firing of visual cells  Discovery of the what pathway by Hubel and Wiesel and neurons inside it that respond to faces shed new light on visual disorders that confused scientists for decades  Vision researchers employ multiple, converging methods when trying to explain the role of the brain in visual experience called McCollough effect Viewing the World in Colour  Perceived colour is a function of dominant wavelength in those mixtures  In visible spectrum, lights with the longest wavelengths appear red and shortest appear violet  perception of colour depends on complex blends of all three properties of light  wavelength is hue, amplitude is brightness and purity is saturation  subtractive colour mixing- works by removing some wavelengths of light leaving less light than was originally there  paint yields subtractive colour mixing because pigments absorb wavelengths reflecting a specific wavelength  additive colour mixing- putting more than one light in the mixture than exists in any one light itself  additive and subtractive colour mixing produces different results  trichromatic theory of colour vision holds human eye has 3 different receptors with different light wavelengths and sensitivities  Helmholtz theorized that the eye contains specialized receptors sensitive to specific wavelengths associated with red, blue and green  Colour blindness is a variety of deficiencies in ability to distinguish colour  Complementary colours are pairs of colours that produce grey tones when mixed together  After image- a visual image that persists after a stimulus is removed  Opponent process theory of colour vision holds that colour perception depends on receptors that make antagonistic responses to three pairs of colours created by Erwald Hering (1878)  It takes both theories of trichromatic theory and opponent process theory to explain colour vision  George Wald demonstrated that eye has three types of cones wit
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