Visual System Structure and Processing (6A) - Psych & Soc

1. What is the functional difference between ON-center and OFF-center ganglion cells?

   ON: fire to light in center; OFF: fire to darkness in center. Opposite responses create contrast detection mechanisms.

2. What is the function of amacrine cells in retinal processing?

   Modulate bipolar-to-ganglion signaling; motion/temporal processing. They integrate signals laterally for complex processing.

3. What is binocular disparity, and what depth cue type does it represent?

   Difference between the two retinal images; a binocular depth cue. Brain computes distance from horizontal image displacement between eyes.

4. Which retinal cells mediate lateral inhibition to enhance contrast?

   Horizontal cells (and amacrine cells in inner retina). Horizontal and amacrine cells provide inhibitory feedback, sharpening edges and improving contrast detection in the retina.

5. What is rhodopsin, and in which photoreceptor is it found?

   Light-sensitive pigment in rods (opsin + retinal). The visual pigment undergoes conformational change when light hits retinal.

6. Which visual field projects to the left cerebral hemisphere?

   Right visual field. Contralateral processing: each hemisphere sees opposite field.

7. Which visual field projects to the right primary visual cortex after the optic chiasm?

   Left visual field. The right visual cortex integrates signals from the left visual field via the optic pathways' decussation pattern.

8. What is the function of the ventral visual stream (the "what" pathway)?

   Object identity processing (form, color); projects to temporal lobe. Processes visual features to recognize objects and faces.

9. What is rhodopsin, and in which photoreceptor is it found?

   Light-sensitive pigment in rods. Rhodopsin absorbs photons in low light, initiating hyperpolarization in rods for scotopic vision.

10. What structure creates the retinal blind spot by lacking photoreceptors?

    Optic disc (optic nerve head). Where ganglion cell axons converge to form the optic nerve, no photoreceptors exist.

11. What is the function of horizontal cells in retinal processing?

    Lateral inhibition to enhance contrast and edge detection. They inhibit neighboring cells to sharpen visual boundaries.

12. What is the function of amacrine cells in the retina?

    Modulate bipolar-to-ganglion signaling; important for motion/temporal processing. They integrate signals across multiple bipolar cells for complex processing.

13. Identify the visual pathway order from retina to primary visual cortex (V1).

    Retina → optic nerve → optic chiasm → LGN → optic radiations → V1. Visual signals relay through thalamus before reaching cortex.

14. Identify the visual deficit from a lesion of the right optic nerve.

    Right monocular blindness. Right optic nerve damage prevents signal transmission from the right retina, resulting in complete vision loss in that eye.

15. What is the ventral visual stream, and which function is it primarily associated with?

    Occipital r temporal; object recognition (what). The ventral stream analyzes form and color for perceptual identification and categorization of visual stimuli.

16. What is the main function of cones in the retina?

    Color (photopic) vision; lower sensitivity, high acuity. Cones contain opsins for detecting different wavelengths.

17. What is the correct sequence of retinal cell types in the vertical pathway?

    Photoreceptors r bipolar cells r ganglion cells. Light activates photoreceptors, which synapse with bipolar cells that relay signals to ganglion cells for output via the optic nerve.

18. What is the difference between magnocellular and parvocellular pathways?

    Magno: motion/low detail; Parvo: color/high detail. Magnocellular layers in LGN handle fast, low-resolution signals for motion, while parvocellular layers process detailed, color information.

19. What is the correct order of visual information flow from eye to cortex?

    Retina r optic nerve r LGN r optic radiations r V1. Visual information flows from photoreceptors in the retina through neural pathways to the primary visual cortex for processing.

20. What are rods specialized for compared with cones?

    Low-light, high sensitivity, low acuity, no color vision. Rods contain rhodopsin that detects dim light efficiently but provides poor resolution and lacks color discrimination.

21. Which structure in the thalamus relays visual information to primary visual cortex?

    Lateral geniculate nucleus (LGN). The LGN organizes retinal inputs into layers, preserving retinotopy before projecting to the visual cortex.

22. What is the function of the cornea in vision?

    Provides most light refraction to focus images on the retina. The cornea bends incoming light rays to converge them onto the retina, accounting for approximately 70% of the eye's refractive power.

23. Identify the lesion: A pituitary tumor compressing the optic chiasm causes what deficit?

    Bitemporal hemianopia (loss of temporal visual fields). Crossing fibers are compressed, affecting peripheral vision from both eyes.

24. What do retinal ganglion cell axons form as they exit the eye?

    The optic nerve (cranial nerve II). Ganglion cells are the output neurons whose axons carry visual signals to the brain.

25. What is the main function of rods in the retina?

    Dim-light (scotopic) vision; high sensitivity, low acuity, no color. Rods contain rhodopsin for detecting low light levels.

26. What is the key retinal neurotransmitter released by photoreceptors in darkness?

    Glutamate. Darkness depolarizes photoreceptors, triggering release.

27. What is the lateral geniculate nucleus (LGN) and where is it located?

    Thalamic relay nucleus for visual input from retina to V1. Part of thalamus that processes visual signals before V1.

28. Which visual field information crosses at the optic chiasm: left or right visual field?

    Both: nasal retinal fibers cross, carrying the contralateral visual field. Nasal fibers from each eye cross to process opposite visual fields.

29. What is the primary function of cones in the retina?

    Color vision and high visual acuity in bright light (photopic) vision. Cones contain photopsins for detecting different wavelengths in bright conditions.

30. What is phototransduction in rods and cones?

    Light converts signals in photoreceptors into neural activity. Photons trigger molecular cascades that hyperpolarize cells.

31. At the optic chiasm, which retinal fibers cross to the opposite hemisphere?

    Nasal retinal fibers decussate; temporal fibers remain ipsilateral. This crossing allows each hemisphere to process both eyes.

32. Which visual field projects to the right cerebral hemisphere?

    Left visual field. Visual fields project contralaterally after chiasm crossing.

33. What is the function of bipolar cells in the retina?

    Relay signals from photoreceptors to ganglion cells. They form the middle layer of the retinal neural circuit.

34. Which pathway is the dorsal stream, and what is its main function?

    Occipital-to-parietal "where/how" pathway for spatial location and motion. Guides actions and tracks movement through posterior parietal cortex.

35. What is the major thalamic relay nucleus for visual information before cortex?

    Lateral geniculate nucleus (LGN) of the thalamus. LGN has 6 layers processing different visual features before cortical relay.

36. What is the accommodation reflex response when shifting gaze from far to near?

    Lens thickens, pupils constrict, and eyes converge. Near triad response mediated by parasympathetic activation.

37. What is the primary function of the lens in the eye?

    Fine-tunes focus by changing shape (accommodation). The lens adjusts its curvature via ciliary muscle contraction to focus on near or far objects, enabling clear vision at varying distances.

38. Identify the visual deficit from a lesion of the left optic tract.

    Right homonymous hemianopia. Left optic tract lesion disrupts signals from the right visual field, causing loss in both eyes' temporal and nasal halves respectively.

39. What retinal change occurs when light activates photoreceptors in phototransduction?

    Photoreceptors hyperpolarize and reduce glutamate release. Light closes cation channels, causing hyperpolarization and decreased neurotransmitter.

40. Identify the visual deficit from a lesion at the optic chiasm.

    Bitemporal hemianopia. Optic chiasm compression severs crossing nasal fibers, leading to loss of temporal visual fields in both eyes.

41. What is the optic disc, and what key feature makes it a blind spot?

    Exit of optic nerve; lacks photoreceptors (no rods or cones). The optic disc forms a physiological blind spot because ganglion cell axons bundle there, displacing photoreceptors.

42. What is the primary visual cortex (V1), and where is it located?

    First cortical visual area in occipital lobe (calcarine cortex). Receives LGN input for initial cortical visual processing.

43. What are cones specialized for compared with rods?

    Color vision and high acuity, best in bright light. Cones express photopsins sensitive to different wavelengths, enabling trichromatic vision and fine detail in photopic conditions.

44. Which retinal cells form the optic nerve by sending axons out of the eye?

    Retinal ganglion cells. Their axons bundle together to carry visual signals to brain.

45. What is the pupil?

    The opening in the iris that allows light into the eye. The pupil's size modulation by the iris controls light entry, protecting the retina and optimizing image clarity.

46. Identify the lesion: Damage to right optic tract causes loss of which visual field?

    Left homonymous hemianopia (loss of left visual field in both eyes). Right tract carries left visual field from both eyes' nasal retinas.

47. What is the function of the dorsal visual stream (the "where/how" pathway)?

    Spatial location and motion processing; projects to parietal lobe. Analyzes movement and guides visually-directed actions.

48. What is the optic chiasm, in terms of which fibers cross?

    Nasal retinal fibers decussate; temporal retinal fibers remain ipsilateral. At the optic chiasm, nasal fibers cross to ensure contralateral representation of visual fields in the brain.

49. What is retinotopic mapping in visual cortex?

    Spatial layout of retina is preserved in V1 cortical representation. Neighboring retinal points map to neighboring cortical areas.

50. What is the role of the iris in the visual system?

    Controls pupil size to regulate light entering the eye. The iris adjusts pupil diameter via sphincter and dilator muscles to optimize retinal illumination under different lighting conditions.

51. What is the primary cortical area that first receives visual input from the LGN?

    Primary visual cortex (V1, striate cortex) in the occipital lobe. V1 contains orientation-selective cells organized in columns.

52. What retinal region provides the highest visual acuity?

    Fovea (within the macula). Dense cone concentration provides sharp central vision.

53. What do retinal ganglion cell axons form as they leave the eye?

    The optic nerve. Ganglion cell axons converge at the optic disc to transmit integrated retinal signals to higher visual centers.

54. What structure is the optic disc, and what key feature does it create in vision?

    Exit of optic nerve; creates the blind spot (no photoreceptors). Axons converge here, leaving no room for photoreceptors.

55. What is the dorsal visual stream, and which function is it primarily associated with?

    Occipital r parietal; motion/spatial processing (where/how). The dorsal stream integrates visual input for guiding actions, processing location and movement in the environment.

56. Which visual field projects to the left primary visual cortex after the optic chiasm?

    Right visual field. Post-chiasm, the left visual cortex processes input from the right visual field due to crossed nasal and uncrossed temporal fibers.

57. Which muscles change lens curvature during accommodation?

    Ciliary muscles. Ciliary muscles contract to relax zonular fibers, allowing the lens to become more spherical for near vision during accommodation.

58. Which pathway is the ventral stream, and what is its main function?

    Occipital-to-temporal "what" pathway for object identity and form. Processes visual features for recognition in inferior temporal cortex.

59. What are bipolar cells in the retina, in terms of information flow?

    Intermediate neurons between photoreceptors and ganglion cells. They relay signals vertically through the retinal layers.

60. What is the name and location of the primary visual cortex?

    V1 in the occipital lobe (calcarine cortex). V1 receives thalamic inputs and performs initial feature extraction like orientation and edge detection.

61. What is the primary function of rods in the retina?

    High light sensitivity for dim-light (scotopic) vision; low acuity. Rods contain rhodopsin for detecting low light levels but lack color discrimination.

62. What is the fovea, and what visual function is it specialized for?

    Central retina; highest visual acuity due to dense cones. The fovea contains a high concentration of cones with minimal convergence, enabling sharp central vision and detailed color perception.

63. What is the function of horizontal cells in retinal processing?

    Lateral inhibition to enhance contrast via photoreceptor-bipolar modulation. They inhibit neighboring photoreceptors to sharpen edges and boundaries.

64. What retinal region has the highest density of cones and greatest acuity?

    Fovea centralis (within the macula lutea). Dense cone packing with no rods creates the sharpest central vision.

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