FEM 4100 Topic 5

1. FEM 4100 Topic 5 Perception Mechanism, Awareness & Attention

2. Overview • The Process of Sensation: Brain waves & perception • Vision • Hearing • Smell and Taste • The Skin Senses • The Spatial Orientation Senses • Influences on Perception • Principles of Perception & Unusual Perceptual Experiences

3. Questions: • The Skin Senses • How does the skin provide sensory information? • What is the function of pain, and how is pain influenced by psychological factors, culture, and endorphins? • The Spatial Orientation Senses • What kinds of information do the kinesthetic and vestibular senses provide? • Influences on Perception • What is gained and what is lost in the process of attention? • How does prior knowledge influence perception? • How does information from multiple sources aid perception?

4. The Process of Sensation: Question address • How is sensory information transmitted to the brain?

5. 1: The Process of Sensation • Sensation • is the process through which the senses pick up visual, auditory, and other sensory stimuli and transmit them to the . • Perception • is the process by which sensory information is actively organized and interpreted by the brain. • Information → organised • Interpretation → brain

6. Just Noticeable Difference (JND) • The smallest increase or decrease in a physical stimulus that is required to produce the “just noticeable difference (JND).” The JND is the smallest change in sensation that a person is able to detect 50% of the time. Which one weighs more? • Weber’s Law states the JND is based on a percentage or proportion of stimulus change rather than a fixed amount of change. • A weight must increase or decrease by 1/50th or 2% for JND • 2 lbs difference needed in 100 lb weight (2% of 100 lb) • a tone must be .33% higher or lower .

7. Sensory Receptors • Are highly specialized cells in the sense organs • detect and respond to one type of sensory stimuli • converts the stimuli into nerve impulses (neural) through transduction process. Converts stimuli into impulses • Sensory Adaptation • The process in which sensory receptors grow accustomed to constant, unchanging levels of stimuli over time. • Smokers grow accustomed to smell of cigarettes

8. Vision: Question to be addressed • How does each part of the eye function in vision? • What path does visual information take from the retina to the primary visual cortex? • How do we detect the difference between one color and another? • What two major theories attempt to explain color vision?

9. 2. Vision The most studied sense • Sensory receptor • A specialized neuron that detects a particular category of physical events/stimulus. • Sensory transduction • The process by which sensory stimuli are transduced into slow, graded receptor potentials. • Receptor potential • A slow, graded electrical potential produced by a receptor cell in response to a physical stimulus.

10. What are the visual stimulus? • Feature detectors: • Neurons in the brain that respond only to specific visual patterns. • Perceived color of light is determined by • Hue(the specific color perceived) • Determined by wavelength. • Brightness • Determined by the intensity of the electromagnetic radiation or light energy that is perceived. • Saturation • Determined by the purity of the light wave or color

11. Vision: What we can/can’t see • Visible Spectrum the band of electromagnetic waves visible to the human eye. • Wavelength – the distance from the peak of a light wave to the peak of the next wave.

12. Saturation (purity) vs Brightness (intensity of light energy)

13. The Anatomy of the Visual System

14. The Eye • Sclera • The white tissue of the eye • Conjunctiva • Mucous membranes that line the eyelid and protect the eye. • Cornea • Tough, transparent, protective layer • Covers front of eye • Bends light rays inward through the pupil

15. The Eye • Lens • Consists of a series of transparent, disk-shaped, onion-like layers behind the iris & pupil • Its shape can be changed by contraction of ciliary muscles. • Changes shape as focusing on objects • Pupil • Adjustable opening in the iris that regulates the amount of light that enters the eye. • Iris • Pigmented ring of muscles situated behind the cornea. • Accommodation • Changes in the thickness of the lens, accomplished by the ciliary muscles, that focus images of near or distant objects on the retina

16. The Eye • Retina • The neural tissue and photoreceptive cells located on the inner surface of the posterior portion of the eye • Contains visual sensory receptors • Rods • Photoreceptor cells in the retina, • sensitive to the light of low intensity • Look like slender cylinders • Allow eye to respond to low light • Cones • Photoreceptor cells in the retina; • maximally sensitive to one of three different wavelengths of light and hence encodes color vision • Enable humans to see color and fine detail • Do not function in very dim light

17. The Eye • Fovea • A small center area of retina that mediates the most acute vision. • Contains only color-sensitive cones. • Has largest concentration of cones • Provides clearest and sharpest vision • Optic Disk • Location on the retina where fibers of ganglion cells exit the eye; responsible for the blind spot (point in each retina with no rods or cones) • Optic Nerve • Caries visual information from retina to both sides of the brain • Primary Visual Cortex • Part of brain which processes visual information

19. From Retinal Image to Meaningful Information

20. Review and Reflect 3.1 Major Structures of the Visual System Structure Their Functions • Cornea • Iris • Pupil • Lens • Retina • Rods • Cones • Fovea • Optic Nerve • Blind Spot • Translucent covering on front of eye that bends light rays inward towards pupil. • Colored part of the eye that adjusts so constant amount of light enters through the pupil. • Opening in the center of the iris through which light enters the eye. • Transparent disk-shaped structure behind pupil that adjusts its shape to allow focusing on objects at varying distances. • Layer of tissue on inner surface of the eye. Contains sensory receptors for vision. • Specialized receptor cells in retina that are sensitive to light changes • Specialized receptor cells in retina that enable humans to see fine detail and color in adequate light. • Small area at center of retina, packed with cones, on which objects viewed directly are clearly and sharply focused. • Nerve that carries visual information from the retina to the brain. • Area in each eye where the optic nerve joins the retinal wall and no vision is possible.

21. Major Structures of the Visual System… Continue • Bipolar cell • A bipolar neuron located in the middle layer of the retina, conveying information from the photoreceptors (rod & cones) to the ganglion cells. • Ganglion cell • A neuron that receives visual information from bipolar cells; its axons give rise to the optic nerve • Horizontal cell • A neuron in the retina that interconnects adjacent photoreceptors and the outer processes of the bipolar cells. • Amacrine cell • A neuron in the retina that interconnects adjacent ganglion cells and the inner processes of the bipolar cells.

24. Theories of Color Vision • Trichromatic Theory • Three types of cones in the retina each make a maximal chemical response to one of three colors. • BLUE, GREEN, or RED. • Each cone is sensitive to one of the colors. • These three colors can then be combined to form any visible color in the spectrum. • EG: when the red and blue cones are simulated in a certain way you will see the colour purple. • Application on colourblindness: • Protanopia (blindness to red): • ‘Red’ cones filled with ‘green’ cones → only see blue and green → red & green -- yellowish • Deuteranopia (blindness to green) • ‘Green’ cones filled with ‘red’ cones → cant see green • Tritanopia (blindness to blue) • Blue cones are damaged or a lack of them → only see in greens and reds → cant differentiate green and yellow (pink).

25. Photoreceptors: Trichromatic coding • Protanopia (blindness to red) • An inherited form of defective color vision in which red and green hues are confused but acute vision is normal; • “Red” cones are filled with “Green” cone cells (absence of L-Cones). • Red appears dark - only two types of cone pigments are present (Green & Blue). • They see the world in shades of yellow and blue; both red and green look yellowish to them. • Deuteranopia (blindness to green) • An inherited form of defective color vision in which red and green hues are confused but acute vision is normal; • “Green” cones are filled with “Red” cone cells (all M-cones are absent). • Only two types of cone pigments are present: Red and Blue. • Cant see the green part but visual acuity is normal. • Tritanopia (blindness to blue) • An inherited form of defective color vision in which “Blue” cones are either lacking or faulty (total absence of S-cones); but acute vision is normal; • See the world in greens and reds. Blue looks green and yellow looks pink. (Cant distinguish blue and yellow) • Resulting in blindness to the blue end of the spectrum.

26. WHICH PICTURE IS MATCH WITH WHICH TYPE OF COLOUR DEFICIENCY?

27. “Color” is determined by the wavelength of a stream of light, by detecting the wavelength of incoming light, the eye can determine what color it is looking at. The (normal) eye contains 3 types of cone cells, each containing a different pigment: • The L-cone detecting long wavelength light (peaking in the yellows – but also responsible for reds). • The M-cone detecting medium wavelength light (peaking in the greens). • The S-cone which detects short wavelength light (peaking with blue). • Your brain determines what color it is seeing by observing the ratio between the signals it receives from each of the three types of cones. Color blindness occurs when one or more types of cones are either totally absent, or has a limited spectral sensitivity.

28. Theories of Color Vision • Opponent-Process Theory • Three kinds of cells respond by increasing or decreasing their rate of firing when different colors are present. • The opponent color process works through a process of excitatory and inhibitory responses, with the two components of each mechanism opposing each other. • For example, red creates a positive (or excitatory) response while green creates a negative (or inhibitory) response. • These responses are controlled by opponent neurons, which are neurons that have an excitatory response to some wavelengths and an inhibitory response to wavelengths in the opponent part of the spectrum.

29. Types of cells: • Red/green – firing increases when red present; green decreases firing (R+G-) • Yellow/blue– firing increases when yellow present; blue decreases firing (Y+B-) • White/black – firing increases when white present, black decreases firing (W+Bl-)

30. The opponent-process theory explains how we see yellow though there is no yellow cone.  • It results from the excitatory and inhibitory connections between the three cone types.  • Specifically, the simultaneous stimulation of red ( L cones) and green (M cones) is summed and in turn inhibits B+Y-, which results in the perception of yellow.  • However, when blue light is present, the S cone is activated, the B+Y- cell receives excitatory input and blue is perceived.

31. COLOR MIXING (Left) vs PIGMENT MIXING (Right) Color mixing: Addition of 2 or more light source. Pigment mixing: Combine 2 types of pigment (such as mixing paint) Thus, OUTCOME IS different CM: Red light + Green light (on white screen) = yellow PM: Yellow + Blue = green

33. Analysis of Visual Information: The Striate Cortex (Primary Visual Cortex or V1) • David Hubel and Torsten Wiesel • 1960s at Harvard University • Discovered that neurons in the visual cortex did not simply respond to light; they selectively responded to specific features of the visual world. • Specific features: • Orientation and movement: Neuron in visual cortex - Simple cell (orientation), complex cell (movement) and hypercomplex cell (orientation). • Spatial frequency: Sine-wave grating and Spatial frequency • Retinal disparity • Color • Two system of visual:Dorsal stream and ventral stream.

34. Analysis of Visual Information: The Visual Association Cortex • Extrastriate cortex • A region of the visual association cortex; receives fibers from the striate cortex and projects to the inferior temporal cortex. • Regions respond to particular features of visual information such as orientation, movement, spatial frequency, retinal disparity, or color. • Dorsal stream • A system of interconnected regions of the visual cortex involved in the perception of spatial location, beginning with the striate cortex and ending with the posterior parietal cortex. • Ventral stream • A system of interconnected regions of visual cortex involved in the perception of form, • beginning with the striate cortex and ending with the inferior temporal cortex.

36. Analysis of Visual Information: The Striate Cortex • Retinal Disparity • The fact that points on objects located at different distances from the observer will fall on slightly different locations on the two retinas; provides the basis for depth perception • Color • Cytochrome oxidase (CO) blob • The central region of a module of the primary visual cortex, revealed by a stain for cytochrome oxidase; contains wavelength-sensitive neurons. • Ocular dominance • The extent to which a particular neuron receives more input from one eye than from the other. • Cortical blindness • Blindness caused by damage to the optic radiations or primary visual cortex.

37. Analysis of Visual Information: The Visual Association Cortex • Studies with humans • Achromatopsia • Inability to discriminate among different hues/shades; caused by damage to the visual association cortex. • Inferior temporal cortex • In primates, the highest level of the ventral stream of the visual association cortex ("What Pathway", is associated with form recognition and object representation); located on the inferior portion of the temporal lobe. • Agnosia • Inability to perceive or identify a stimulus by means of a particular sensory modality. • Visual agnosia • Deficits in visual perception in the absence of blindness; caused by brain damage. • Apperceptive visual agnosia • Failure to perceive objects even though visual acuity is relatively normal.

38. Analysis of Visual Information: The Visual Association Cortex • Analysis of form (what do you see?) • Prosopagnosia • Failure to recognize particular people by the sight of their faces. • Associative visual agnosia • Inability to identify objects that are perceived visually, even though the form of the perceived object can be drawn or matched with similar objects. • Perception of movement (how thing move?) • Fusiform face area • A region of the extrastriate cortex located at the base of the brain; involved in perception of faces and other objects that require expertise to recognize. • Akinetopsia • Inability to perceive movement, caused by damage to area V5 of the visual association cortex.

39. Neural Circuitry in the Retina

40. Neural Circuitry in the Retina • The photoreceptors → contain light-absorbing pigment molecules. • In the dark: Photoreceptors constantly release neurotransmitter (negatively charged) – hyperpolarised dendrite of bipolar cell • Thus, when light strike → it does not cause the neuron to depolarize → instead, the photoreceptor does exactly the opposite. • When pigment molecules in a photoreceptor cell absorb a photon of light → sodium gates (neg. charged) in the membrane of the cell close, and the neuron becomes hyperpolarized.

41. This means → the photoreceptor is no longer generating an action potential → so it is not delivering inhibitory neurotransmitters to the bipolar cell(s) it synapses with. • Since the bipolar cells are no longer receiving inhibitory neurotransmitters from the photoreceptors → they depolarize and generate action potentials. • The neurotransmitters released by the bipolar cells are excitatory→ cause the ganglion cells they synapse with to depolarize and generate action potentials of their own. • And since the optic nerve is just the axons of the ganglion cells, the impulses are relayed to the brain.

42. Pathway: Stimulus from eye to brain • DARK → photoreceptor (release inhibitory NT) → LIGHT → photoreceptor (stop inhibitory NT) → bipolar cell (excitatory NT) → ganglion cell (increase firing) → Axon of ganglion cell (optic nerve) → BRAIN • Brain → Thalamus → Primary visual cortex

43. COLOR MIXING (Left) vs PIGMENT MIXING (Right) Color mixing: Addition of 2 or more light source. Pigment mixing: Combine 2 types of pigment (such as mixing paint) Thus, OUTCOME IS different CM: Red light + Green light (on white screen) = yellow PM: Yellow + Blue = green

44. WHICH PICTURE IS MATCH WITH WHICH TYPE OF COLOUR DEFICIENCY?