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chapter 3 - Sensation and perception 2013


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chapter 3 - Sensation and perception 2013

  1. 1. Sensation & Perception
  2. 2. What’s the difference?Sensation Detecting stimuli from the body or environmentPerception Organizing sensations into meaningful patternsStimulus Form of energy that can affect sense organs
  3. 3. SensationSensory receptors Detect stimuli & convert energy into neural impulses Receptors are designed to serve very specific functions
  4. 4. Thresholds and Stimulus ChangeThresholds There is a minimum amount of any given sensation that has to be present for us to notice it Absolute threshold This is the minimum amount of a stimulus that is necessary for us to notice it 50% of the timeSensory adaptation If a stimulus is unchanging, we become desensitized to it Keeps us focused on changes, not constants
  5. 5. VisionElectromagnetic energy Long wavelengths: AC circuits, radio waves, infrared rays Short wavelengths: visible light, X-rays, UV & gamma rays Other animals can see other segments of the spectrum of electromagnetic energy Bees can see ultraviolet rays and blue-violet, but not red Pit vipers can see infrared rays Dogs can’t see all the colors that humans can (no red)
  6. 6. Our Visible SpectrumRed Orange Yellow Green Blue Indigo VioletHue determines color Depends on length of the distance from one peak to the next on the waveIntensity determines brightness Depends on amplitude of the waveTransduction The process where the eye converts electromagnetic energy (light) into nerve impulses
  7. 7. The Eye
  8. 8. Parts of the EyeCornea Light is initially focused by this transparent covering over the eyePupil Light enters the eye through this openingIris Muscle connected to the pupil that changes its size to let in more or less light Everyone has a unique iris (thus it is a new security technique being employed by some organizations)
  9. 9. Parts of the EyeLens This flexible disk under the cornea focuses light onto the back of the eye Accommodation Flexibility of the lens allows eye muscles to adjust light from objects at various distances awayRetina Light reflected from the lens is received by this sheet of tissue at the back of the eye Contains the receptors that convert light to nerve impulses
  10. 10. How we see color: ConesRetinal cells that respond to particularwavelengths of light, allowing us to seecolor Most of our cones are located on the fovea, which gives us the sharpest resolution of visual stimuli 3 types of cones, each sensitive to different light frequencies
  11. 11. How we see in the dark: RodsRetinal cells that are very sensitive to light butonly register shades of gray (i.e., no color)Rods are located everywhere in the retinaexcept in the fovea Rods allow us to see at night without strong light – this is why we see less color at night Because of where the rods are on the retina, we see best at night without light in the periphery of our visionDark adaptation
  12. 12. Rods & Cones
  13. 13. Optic NerveFrom the receptor cells in the retina, theconverted impulse from light is directed to theoptic nerve This is the large bundle of nerve fibers that carry impulses from the retina to the brain It sits on the retina but contains no cones or rods, so this is where you experience a ‘blind spot’ We aren’t aware that we have a blind spot because our brain completes patterns that fall across our blind spot and because our eyes are constantly moving (‘filling’ it in) Pg 149 in book - an activity to demonstrate this
  14. 14. Processing of Visual InformationRetina Processes electrical impulses, starts to encode and analyze sensory information (at the most basic level)Optic Nerve Neurons pick up the messages from retina, transmit to the thalamus, then on to the visual cortex, then on to more specified areas
  15. 15. Visual perception PrinciplesDuring organisation and interpretation thevisual cortex applies rules to understand theinformation. We tend to automatically usethese without any conscious effort. There are 3 categories: Gestalt principles Depth principles Perceptual constancies
  16. 16. Gestalt Principles of VisionFigure-ground We recognize objects (figures) by distinguishing them from the background (ground)
  17. 17. Closure We tend to fill in gaps in a figure
  18. 18. Similarity Parts of an image that look alike tend to be grouped together
  19. 19. Proximity Parts of an image that are near one another tend to be grouped together
  20. 20. Depth PrinciplesHow is it that we perceive a 3-dimensional world whenour eyes only project a 2-dimensional image on ourretinas??!Our brain uses different cues to perceive depth. Thereare 2 types: Binocular depth cues (convergence, retinal disparity) Monocular depth cues (accommodation, pictorial cues – linear perspective, interposition, texture gradient, relative size, height in the visual field
  21. 21. Binocular depth cuesOur brain uses both eyes working together to provideinformation about depth and distance (this is especiallyimportant for objects that are close). Convergence The brain detecting depth and distance from the changes in the tension in the eye muscles that occur when the two eyes turn inward to focus on an object
  22. 22. Retinal disparity Refers to the difference in the location of the visual image on the retina (due to the angle of the view)
  23. 23. Monocular depth cuesMonocular cuesOur brain also uses information from the stimulus thatrequires the use on only one eye. Accommodation Pictorial cues Linear perspective Interposition Texture gradient Relative size Height in the visual field
  24. 24. Accommodation Involves the automatic adjustment of the shape of the lens to focus an object in response to changes in how far away that object is.
  25. 25. Monocular – pictorial depth cuesLinear perspective Is the apparent convergence of parallel lines as they recede (go back ) into the distanceInterposition Occurs when one object partially block or covers another and therefore the one behind is perceived as further away
  26. 26. Texture gradient The gradual reduction of detail that occurs in a surface as it recedes into the distanceRelative size The tendency to visually perceive the object that produces the larger image on the retina as being closer
  27. 27. Height in the visual field Refers to the location of objects in out field of vision, whereby object that are located closer to the horizon are perceived as being more distant than objects located further from the horizon
  28. 28. Perceptual Constancies - VisionThe image of an object on your retina can very insize, shape, and brightness But we still continue to perceive the object as stable in size, shape and brightness Size constancy Shape constancy Brightness constancy
  29. 29. SizeConstancy The tendency to view an object as constant in size despite changes in the size of its image on the retina (as we move)
  30. 30. ShapeConstancy The tendency to see an object as retaining its form despite changes in orientation
  31. 31. BrightnessConstancy The tendency to perceive an object as maintaining its level of brightness in relations to its surroundings