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1. Sensation and Perception Sensation: The process by which our sensory receptors / nervous system receives and represents stimulus energy Perception: The process of organizing and interpreting sensory information, which enables us to identify meaningful events and/or objects

2. Sensation and Perception Bottom-Up Processing -analysis that starts with the basic sensory information and moves on to higher levels of processing (integration of sensory info) - the kinds of higher-level processing employed can be determined by low-level (I.e., sensory level) features of the input

3. Sensation and Perception Top-Down Processing - analysis that starts with a high-level organizational structure, and works down to sensory level information - the kinds of higher-level organizational structures used can determine what sensory info is (or is not) relevant to the task at hand

4. Bottom-up Top-down MOTION Sensation and Perception Both top-down and bottom-up processing may be involved in the perception of a physical stimulus

5. “Its an animal” Sensation and Perception The perception of motion (low level sensory feature) activates the relevant high level concept Bottom-up Top-down MOTION

6. Size Texture Taste Sensation and Perception The activated concept of “animal” determines what low level features will be important / relevant “Its an animal” Bottom-up Top-down MOTION

7. Sensation and Perception Psychophysics - how do the objective, physical features of a sensory stimulus relate to the subjective experience of those stimuli? - e.g., is a 100 watt light perceived as 2x as bright as a 50 watt light?

8. Sensation and Perception Psychophysics Absolute Threshold: the minimum intensity of a stimulus that is detectable (usually 50% correct detection is the standard used) - e.g., how bright does a light have to be before you can detect iton 50% of the trials where the light is actually presented?

9. Sensation and Perception Psychophysics Difference Threshold: the minimum change in the intensity of a stimulus that is detectable. This is called a JND (Just Noticeable Difference) - e.g., how much brighter does one light have to be than another light before you can tell that one is brighter than the other?

10. Sensation and Perception Psychophysics Weber’s Law: The difference in physical intensity required to create a subjective JND is a constant proportion of the absolute intensity of the stimuli. - i.e., the JND can be described as a constant percentage difference across a range of stimulus ‘strength’

11. Sensation and Perception Sensory Adaptation - we have evolved perceptual processes that are designed to alert us to informative changes in the environment - sensory input that is unchanging tends to be disregarded (most of the time) at higher levels of processing

12. Sensation and Perception Transduction -the conversion of stimulus energy into electro-chemical signals in the CNS

13. Sensation and Perception Transduction -the conversion of stimulus energy into electro-chemical signals in the CNS -performed by specialized neurons in each sensory system

14. Sensation and Perception Visual Transduction Wavelength: the objective distance between peaks of a waveform Hue: (color) the subjective consequence of wavelength in light

15. Sensation and Perception Visual Transduction Amplitude: (intensity) the objective physical ‘height’ of waves in a waveform Brightness: the subjective consequence of amplitude in light

16. Sensation and Perception Visual Transduction Complexity: the objective physical ‘composition’ of waves in a waveform Saturation: the subjective consequence of complexity in light

17. Sensation and Perception Visual Transduction What we see is only a very small fraction of what is out there

18. Sensation and Perception The Eye Accomodation: muscles change the shape of the lens to focus on objects at different distances

19. Sensation and Perception The Eye Rods and Cones - there are two types of receptor cell in the retina, rods and cones - cones (colour vision) are concentrated in the fovea (area of central focus) - rods (black/white vision) are concentrated in the periphery (none in the fovea)

20. Sensation and Perception The Eye Rods and Cones - cone cells respond to red, blue or green wavelengths of light to produce colour info - cone cells also the most sensitive to visual detail, rod cells in the peripheral visual field are better ‘motion detectors’ - fovea is all cones, few cones in the periphery

21. Sensation and Perception Visual Processing - information is processed at increasingly abstract levels as it passes through the visual system - some processing at the retinal level… - some retinal ganglion cells may fire only when they receive a certain pattern of input from bipolar/receptor cells (e.g., ‘bug detector’ cells in the frog eye)

22. Sensation and Perception Feature Detection -feature detector cells in the visual cortex respond to particularbasic features of the input (edges, lines, orientation, direction of movement, etc…) - at the next level, cells respond to particular combinations of features - processing continues through multiple levels until content is identified

23. Sensation and Perception Feature Detection - sometimes the activation of certain feature detectors can result in the perception of visual objects that are not really there

24. Sensation and Perception Feature Detection - ambiguous features can cause our perceptions to change / alternate The Necker Cube - which is the ‘front’ surface of the cube?

25. Sensation and Perception Parallel Processing - computer CPUs process information serially (one piece at a time, but at a high speed) - the visual system processes several different streams of information in parallel (at the same time, but slower)

26. Sensation and Perception Parallel Processing - a failure or interruption of one processing stream (e.g., colour processing) may not disrupt other streams

27. Sensation and Perception Parallel Processing …so motion, form, depth, etc… are still percieved, but all visual images are in black and white

28. Sensation and Perception Parallel Processing - if visual processing was serial, a problem anywhere in the system would probably result in complete blindness

29. Sensation and Perception Parallel Processing - many visual problems resulting from brain damage indicate the parallel nature of visual processing - e.g., failure to perceive colour - e.g., failure to perceive motion - e.g., failure to perceive complex forms

30. Sensation and Perception Colour Vision Trichromaticcolour theory - cone cells respond to 1 of 3 primary colours of light (red, green, and blue) - this colour info is combined through additive mixing to represent all other colours - there is strong evidence that this is true at the retinal level

31. Sensation and Perception Colour Vision Opponent-Process Theory - people who are red-green colourblind lack either ‘red’ or ‘green’ cone cells - yellow is a combination of red and green light - people who are red-green colourblindcan still see yellow as a colour (????)

32. Sensation and Perception Colour Vision Opponent-Process Theory 3 (or 6) types of ‘opponent-process’ cells: Red-GreenGreen-Red Blue-YellowYellow-Blue Black-WhiteWhite-Black One colour turns cell ‘on’, the other colour turns cell ‘off’

33. Sensation and Perception Colour Vision - while processing is clearly trichromatic at the retinal level, there certainly seems to be some opponent-process involved en route to the visual cortex

34. Sensation and Perception Colour Constancy - the perception of colour depends on the context (colour of surroundings), as well as the actual colour of the object

35. Sensation and Perception Perceptual Illusions Why are visual illusions so common? - visual capture - humans are primarily visually-oriented organisms - when conflicting info comes in through different modalities, the brain: a) assumes the visual version is ‘true’ b) alters other sensory info to match it

36. Sensation and Perception Perceptual Organization Gestalt – an overall form or whole - “the whole is more than the sum of the parts” - how do we organize separate elemental sensations into a perceived “whole”?

37. Sensation and Perception Perception of Form Figure vs. Ground - figure and ground may ‘flip’, but we always make the distinction between the two

38. Sensation and Perception Perception of Form Grouping There are 5 basic principles for grouping objects…

39. Sensation and Perception Perception of Form Proximity – grouping things that are close together in space

40. Sensation and Perception Perception of Form Similarity – grouping similar things together

41. Sensation and Perception Perception of Form Continuity – we will see a smooth, continuous pattern, rather than an interrupted, discontinuous pattern

42. Sensation and Perception Perception of Form Connectedness – areas / objects that are uniform and linked are perceived as a single object

43. Sensation and Perception Perception of Form Closure – we will fill in ‘gaps’ to create the ‘appropriate’ objects

44. Sensation and Perception Perception of Distance Binocular Cues - retinal disparity - convergence

45. Sensation and Perception Perception of Distance Monocular Cues - interposition

46. Sensation and Perception Perception of Distance Monocular Cues - relative size

47. Sensation and Perception Perception of Distance Monocular Cues - relative clarity

48. Sensation and Perception Perception of Distance Monocular Cues - texture gradient

49. Sensation and Perception Perception of Distance Monocular Cues - relative height

50. Sensation and Perception Perception of Distance Monocular Cues - motion parallax