Sensation

1. Psychophysics • Thresholds (include JND) • Attention and discrimination • Inattentional blindness • Change blindness • Pop-out phenomenon • Stroop Effect Sensation

2. Sensation & Perception How do we construct our representations of the external world? To represent the world, we must detect physical energy (stimulus) from the environment and convert it into neural signals, a process called sensation. When we select, organize, and interpret our sensations, the process is called perception.

3. Psychophysics • Studies the links between physical stimuli in the world and the psychological experience of those stimuli • Fechner, Wundt, Titchener, Weber • Among the earliest research to be conducted in the field of Psychology

4. Bottom-up Processing (sensation) Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind. Letter “A” is sensed as a black blotch decomposed into features by the brain and perceived as an “A” by our mind .

5. Top-Down Processing (perception) Information processing guided by higher-level mental processes as we construct perceptions drawing on our experience and expectations. THE CHT

6. Making Sense of Complexity Our sensory and perceptual processes work together to help us sort out complex images. “The Forest Has Eyes,” Bev Doolittle

7. Exploring the Senses • What stimuli cross our threshold for conscious awareness? • Could we be influenced by stimuli too weak (subliminal) to be perceived? • Why are we unaware of unchanging stimuli, like a band-aid on our skin or the feeling from our shoes?

8. Thresholds Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time. For example, young children generally have a lower absolute threshold for sounds since the ability to detect sounds at the lowest and highest ranges tends to decrease with age.

9. Subliminal Threshold When stimuli are below one’s absolute threshold for conscious awareness. Detect it less than 50% of the time

10. Difference Threshold Difference Threshold: Minimum difference between two stimuli required for detection 50% of the time, also called just noticeable difference (JND). For example, if you were asked to hold two objects of different weights, the just noticeable difference would be the minimum weight difference between the two that you could sense half of the time.

11. Weber’s Law explains the JND Two stimuli must differ by a constant minimum proportion (rather than a constant amount), to be perceived as different. Weber fraction: k = dI/I.

12. Signal Detection Theory • Predicts when we will detect weak signals • Ask why people respond differently to the same stimuli?? • Why does the same person’s response vary as the circumstance changes • Sensitivity and responsiveness increases with emotional state • Example: Hearing your baby cry…

13. Sensory Adaptation Diminished sensitivity as a consequence of constant stimulation. Sometimes referred to as habituation Put a band aid on your arm and after a while you don’t sense it.

14. Selective Attention Perceptions about objects change from moment to moment. Different forms of Necker cube become available to our perception, however, one can pay attention only to one aspect of the object. Necker Cube

16. Selective Attention • Discrimination • we have the ability to filter out stimuli rather than process every single stimuli that is bombarding our sensory receptors, will be helpful in conditioning (learning by association) • Cocktail party effect • the ability to focus one's listening attention on a single talker among a mixture of conversations and background noises, ignoring other conversations.

18. Inattentional Blindness Inattentional blindness refers to inability to see a an object or a person amidst an engrossing scene. Keep your eye on the ball and count how many times the team with the white shirts passes it…

19. Change Blindness Change blindness is a form of inattentional blindness, where two-thirds of direction giving individuals failed to notice a change in the individual who was asking for directions.

20. Pop-out phenomenon • A powerful and distinct stimulus demands our attention • We don’t choose to see them, can’t ignore it • A type of automatic processing Automatic processing Controlled processing

21. Stroop Effect • Our brain can process information faster when it is presented in the way we expect it • When too many areas of our brain are active, we have a pause in our processing • Try this…http://faculty.washington.edu/chudler/java/ready.html

22. Name the color of the font

23. AP stuff • Stimulus attention • Selective attention (cock-tail party) • Stimulus discrimination • Habituation • Thresholds • Absolute (detectable greater than 50% of time) • Subliminal (detectable less than 50% of time) • Just noticeable difference (Weber’s Law) • It’s a proportion of the original stimulus

24. Vision • Types of Transduction • Light and Sound Characteristics • Parts of the eye • The process of vision • Cells within the retina • Shape Detectors and Feature Detectors • Theories of vision

25. Transduction In sensation, transformation of stimulus energy into neural impulses. Phototransduction: Conversion of light energy into neural impulses that brain can understand (the rods and cones in the retina) Auditory/Acoustic transduction: Conversion of sound waves into neural impulses (the cilia in the cochlea)

26. Light Characteristics • Wavelength (hue/color) • Intensity (brightness) • Saturation (purity)

27. Wavelength (Hue) Hue (color):dimension of color determined by wavelength of light. Wavelengththe distance from the peak of one wave to the peak of the next.

28. Intensity (Brightness) IntensityAmount of energy in a wave determined by amplitude; related to perceived brightness.

29. The Eye

30. Parts of the eye • Cornea: Transparent tissue where light enters the eye. • Iris: Muscle that expands and contracts to change the size of opening (pupil) for light. • Lens: Focuses the light rays on the retina. • Retina: Contains sensory receptors that process visual information and send it to the brain.

31. The Lens Lens: Transparent structure behind pupil that changes shape to focus images on the retina. Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.

32. The Lens Fovea Nearsightedness: A condition in which nearby objects are seen more clearly than distant objects. Farsightedness: A condition in which faraway objects are seen more clearly than near objects.

33. Retina Retina: The light-sensitive inner surface of the eye, containing receptor rods and cones plus layers of other neurons (bipolar, ganglion cells) that process visual information.

34. Bipolar & Ganglion Cells Bipolar cells receive messages from the photoreceptor cells (rods and cones)and transmit those messages to ganglion cellswhich have long axons that are intertwined and form the optic nerve.

35. Optic Nerve, Blind Spot & Fovea Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where optic nerve leaves the eye, because there are no receptor cells located here, it creates a blind spot. Fovea: Central point in the retina, around which the eye’s cones cluster. http://www.bergen.org

36. Test your Blind Spot Use your textbook. Close your left eye, and with the right eye fixate on the black dot. Move the page towards and away from your eye. At some point the car on the right will disappear due to blind spot. Or, take a piece of paper, roll it up, look through it with one eye and bring your opposite hand next to the paper. There should be a hole in your hand!!!! (thanks Emilie B.)

37. Photoreceptors E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969 Why don’t they see which color it is?

39. Feature Detection Nerve cells in the visual cortex respond to specific features, like edges, angle, and movement. Feature detectors allow us to see the lines, motion, curves of this power point slide What happens when you overwhelm these feature detectors? Watch the center of the spiral…

40. Shape Detection Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses. Ishai, Ungerleider, Martin and Haxby/ NIMH

41. Perception in Brain Our perceptions are a combination of sensory (bottom-up) and cognitive (top-down) processes.

42. Visual Information Processing Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form and movement etc. Watch the car video closely and note the different forms of processing that are occurring simultaneously…

43. 2 Theories of Color Vision Trichromatic theory: Based on behavioral experiments, Young-Helmholtz suggested that retina contains three receptors sensitive to red, blue and green colors.

44. Color Blindness Genetic disorder in which people are blind to green or red colors supports Trichromatic theory.

45. Opponent Process Theory • As our receptor cells sense colors in our environment, the cones are also firing the opponent (opposite) color BlackWhiteRedGreenBlueYellow Gaze at the middle of the flag for about 30 seconds…

46. Afterimage Effect

48. Dark adaptation • The process by which the rods and cones adjust to changes in levels of light • Rods are more sensitive to light and so take longer to fully adapt to the change in light • The fovea is blind to dim light (due to its cone-only array) and the rods are more sensitive • Insufficient adaptation to dark environment, called “night blindness”.

49. Color Constancy Color of an object remains the same under different illuminations. However, when context changes color of an object may look different. R. Beau Lotto at University College, London

50. AP stuff… • Cornea-pupil-lens-retina-photoreceptors-bipolar-ganglion-optic nerve-visual cortex • Photo transduction takes place in the rods (light) and cones (color) • Fovea is the point of focus (what happens if..) • Why a blind spot? • Real image and virtual image (WOW!) • Remember frequency and amplitude