Physiological Psychology

1. Physiological Psychology Vision I

2. Sensation and perception Sensation – The process in which the sense organs’ receptor cells are stimulated and relay information to the brain. Perception – The process in which an organism selects and interprets sensory input so that it acquires meaning Sensation – Detect Stimuli Perception - Comprehension

3. Vision Conversion of light energy to graphical information that the brain can “see” visual receptors are specialized to absorb light and transduce it into an electrochemical pattern in the brain not a duplicate, picture-like pattern of the object

5. Cornea – the transparent tissue covering the front of the eye Sclera – the tough outer layer of the eye; the “white” of the eye Iris – The pigmented muscle of the eye that controls the size of the pupil Lens – The transparent organ situated behind the iris of the eye; helps focus an image on the retina Accommodation - The change in the shape of the lens to adjust for distance

6. Vitreous Humor – the clear fluid in the eye Retina – the tissue at the back inside surface of the eye that contains the photoreceptors Macula - 3mm X 5mm center of retina with greatest ability to resolve detail Fovea – Small pit near the center of the retinal containing many receptors responsible for the most acute and detailed vision

8. The Retina Light passes through ganglion and bipolar cells, without distortion, to visual receptors bipolar cells receive input from visual receptors ganglion cells receive input from bipolar cells amacrine cells exchange information with bipolar cells and send information to ganglion and other amacrine cells provides many options for complex processing of information Optic nerve is made up of axons of ganglion cells the point where optic nerve leaves the eye does not have receptors and is our blind spot

11. Many bird species have two foveas per eye one pointing ahead and one pointing to the side Visual receptors in some predators and prey are designed to facilitate survival hawks have greater density on top half (looking down) than on the bottom half (looking up) rats have greater density on the bottom half (looking up)

12. Photoreceptors Two types: Rods and Cones Rods – Very sensitive to light but cannot detect changes in color respond best to low light conditions bleached by bright light Cones – responsible for acute daytime vision and color vision Distribution different: Cones almost entirely in fovea, rods spread across

13. 100 million cones and 6 million rods But rods send 10 times more responses to brain than cones Each cone has direct line to brain while many rods share same line Both rods and cones contain photopigments, chemicals that release energy when struck by light light is absorbed and 11-cis-retinal is converted to all-trans-retinal

14. Color Vision Rods specialize in picking up very dim light while cones specialize in fine detailed vision and color vision. Colors of light correspond to different wavelengths of electromagnetic energy Something has color because of the wavelength of light that it reflects White reflects all wavelengths Black absorbs all wavelengths How does the visual system convert these wavelengths into our perception of color?

15. Psychological dimensions of color Hue – Color: the psychological property of light referred to as color Based on the wavelength of the light Brightness – The lightness or darkness of reflected light Based on the intensity of the light Saturation – Purity: the depth and richness of the hue Based on the mixture of several wavelengths

17. Theories of Color Vision Trichromatic theory- or the Young Helmholtz theory Cones respond to three primary colors Blue Green Red Separate type of cone for each primary color Color vision depends on the relative rate of response by 3 types of cones.

18. 3 types of cones

19. Opponent Process Theory There are 6 basic colors to which people respond, but 3 types of receptors Red-green Blue-yellow Black-white We perceive color in terms of “paired opposites” red-green, black-white and yellow-blue explains why we can’t see reddish green or bluish yellow explains negative color afterimages

20. Support for opponent-process Negative afterimages- Image seen after a portion of the retina is exposed to an intense visual stimulus A negative afterimage consists of colors complementary to those of the physical stimulus When the cones have been fatigued, the opposite color comes through.

21. Color afterimage

25. Opponent-processes for Detection of Movement? http://psylux.psych.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/html/motion_aftereffect.html

26. Opponent processes is not a complete explanation since afterimages depend not only on the retina but also on the area of the brain that produces it. Ex. McCollough effect Research has found that trichromatic theory and opponent-process theory are both wrong and right Cones are probably like Trichromatic theory Bipolar cells may be opponent processes

28. The retinex theory color perception requires some reasoning the cortex compares information from various areas of the retina to determine the brightness and color perception for each area color constancy: we see the right colors despite lighting changes, e.g., we subtract green tint to see white house and red rose but we only see green house if viewed in isolation brightness requires a comparison with other objects

29. Visual perception depends on both bottom-up and top-down processing. Bottom-up processing Data-driven- raw sensory information We see something and interpret what we see. Top-down processing Conceptually driven Uses past experiences to interpret information We see something and interpret it based on our previous knowledge and expectations “From the brain” Causes illusions

32. Abnormal Color Vision: Color Blindness

34. Red-green color blindness – are missing either a red or green cone. inability to distinguish red from green is most common deficiency recessive gene on X chromosome 8% in men and 1% in women Lack of blue cones also exists, but is extremely rare. Others may lack cones altogether and thus do not see color. Acquired achromotopsia – damage to parts of the occipital cortex. Lose ability to see aspects of color.

35. Visual Pathways Within the eyeball rods and cones synapse to horizontal cells and bipolar cells horizontal cells make inhibitory synapse onto bipolar cells bipolar cells synapse to amacrine and ganglion cells axons of the ganglion cells leave the back of the eye

38. The inside half of the axons of each eye cross over in the optic chiasm most visual information goes through the lateral geniculate nucleus of the thalamus some goes to the superior colliculus LGN inputs to other parts of thalamus and to visual areas of cerebral cortex, which sends back axons to modify input

39. Processing in the Retina Receptive field: the point in space from which incoming light strikes a receptor receptors have both excitatory and inhibitory regions since receptive field is normally an array of light patterns Ex: light in center of ganglion cell might be excitatory, with the surround inhibitory Lateral inhibition each active receptor and it’s visual path tends to inhibit the visual path of neighboring receptors Increases contrasts in the image

40. An active receptor excites both a bipolar and horizontal cell; in turn, horizontal cell inhibits bipolar cell, but net potential is excitatory on bipolar But, horizontal cell does inhibit neighboring bipolar cells on border of visual field Effect is to heighten contrast: receptors inside visual field are excited and those on border tend to be inhibited

42. Retina and Lateral Geniculate Pathways Parvocellular: smaller ganglion cell bodies and small receptive fields, located near fovea detect visual detail and color all axons go to lateral geniculate nucleus Magnocellular: larger ganglion cell bodies and receptive fields, distributed fairly evenly throughout retina respond to moving stimuli and patterns not color sensitive most axons go to lateral geniculate nucleus

43. Koniocellular: small ganglion cell bodies that occur throughout the retina many functions axons go to lateral geniculate nucleus, thalamus and superior colliculus Many different types of ganglion cells implies analysis of information from the beginning

44. Most visual information from lateral geniculate nucleus goes to primary visual cortex (V1) first stage of visual processing Output of V1 goes to secondary visual cortex (V2) second stage of visual processing which transmits visual information to additional areas feedback loop to V1 V1 and V2 also exchange information with other cortical areas and thalamus 30-40 visual areas reported in brain of macaque monkey

45. Magnocellular and parvocellular paths split into three paths Magnocellular path ventral branch to temporal cortex is sensitive to movement dorsal branch to parietal cortex integrates vision with action Parvocellular path to temporal cortex is sensitive to details of shape Mixed parvo/magnocellular path to temporal cortex is sensitive to brightness and color

47. Visual paths in temporal cortex form the ventral stream the “what” path, specialized for identifying and recognizing objects if damaged, we can find and pick up objects but cannot describe them Visual path in parietal cortex is the dorsal stream the “where” or “how” path, helps motor system find objects, move toward them and pick them up if damaged, we can describe object but can’t find and pick up object