Eye movements and visual stability Kandel et al Ch 29, end of Wolfe Ch 8

1. Eye movements and visual stability Kandelet al Ch29, end of Wolfe Ch 8 KandelCh 39 for more info.

2. Is a set of Reichardt detectors is sensitive to motion in one direction and only in a particular speed? It seems like an inefficient design since a great number of neurons will be required to encode motion in all possible directions and speed, unless each of them can actually encode for a small range of speed, although that might lower the sensitivity to speed change. Or the visual cortices simply have enough neurons to do so. I also want to know if information about the motion of objects stays in MT/MST etc or is it  transferred to other areas to bind with other properties of objects that allow recognition of moving objects. Again the binding problem. The reason I asked the binding question again is because the integration between properties of object in the dorsal stream (eg. motion signals in MT) and properties in the ventral stream (eg. orientation and shape for object recognition) must differ somehow from integration within ventral stream for 'what' information. Referring to Campbell and Robson's experiment, the lecturer mentioned that if the cells adapt to seeing an upward motion, they will notice a "downward" motion after the motion stops. Is this the same kind of adaptation that sees an opposite color when the color disappears (like in the rotating color circle that we saw two weeks ago)?

4. Why do we move our eyes? - Image stabilization - Information acquisition

5. Visual Acuity matches photoreceptor density

6. Why do we move our eyes? 1. To bring objects of interest onto high acuity region in fovea.

7. Cone Photoreceptors are densely packed in the central fovea

8. Visual Angle x a d tan(a/2) = x/d a = 2 tan-1 x/d Why eye movements are hard to measure. A small eye rotation translates into a big change in visual angle 18mm 1 diopter = 1/focal length in meters 55 diopters = 1/.018 0.3mm = 1 deg visual angle

9. Why do we move our eyes? 1. To bring objects of interest onto high acuity region in fovea. 2. Cortical magnification suggests “enhanced” processing of image in the central visual field.

10. Oculomotor Muscles Muscles innervated by oculomotor, trochlear, and abducens (cranial) nerves from the oculomotor nuclei in the brainstem. Oculo-motor neurons: 100-600Hz vs spinal motor Neurons: 50-100Hz

11. Types of Eye Movement Information GatheringStabilizing Voluntary (attention) Reflexive Saccades vestibular ocular reflex (vor) new location, high velocity (700 deg/sec), body movements ballistic(?) Smooth pursuit optokineticnystagmus (okn) object moves, velocity, slow(ish) whole field image motion Mostly 0-35 deg/sec but maybe up to100deg/sec Vergence change point of fixation in depth slow, disjunctive (eyes rotate in opposite directions) (all others are conjunctive) Note: link between accommodation and vergence Fixation: period when eye is relatively stationary between saccades.

12. Retinal structure Accomodation:tension on zonulefibres

13. Acuity – babies Acceleration Depth-dept gain, Precision in natural vision Velocity Ocular following - Miles

14. otoliths Rotational (semi-circular canals) translational (otoliths)

15. VOR Latency of vestibular-ocular reflex=10msec

16. Demonstration of VOR and its precision – sitting vs standing It is almost impossible to hold the eyes still.

18. Step-ramp allows separation of pursuit (slip)and saccade (displacement) Saccade latency approx 200 msec, pursuit approx 100 – smaller when there is a context that allows prediction.

19. “main sequence”: duration = c Amplitude + b Min saccade duration approx 25 msec, max approx 200msec

20. Demonstration of “miniature” eye movements Drift Micro-saccades Tremor Significance?? It is almost impossible to hold the eyes still.

21. What’s involved in making a saccadic eye movement? Behavioral goal: make a sandwich Sub-goal: get peanut butter Visual search for pb: requires memory for eg color of pb or location Visual search provides saccade goal - attend to target location Plan saccade to location (sensory-motor transformation) Coordinate with hands/head Calculate velocity/position signal Execute saccade/

22. Brain Circuitry for Saccades 1. Neural activity related to saccade 2. Microstimulation generates saccade 3. Lesions impair saccade Dorso-lateral pre-frontal V1: striate cortex Basal ganglia Oculomotor nuclei

23. Function of Different Areas monitor/plan movements target selection saccade decision saccade command (where to go) inhibits SC V H signals to muscles (forces)

24. Cells in caudate signal both saccade direction and expected reward. Hikosaka et al, 2000 Monkey makes a saccade to a stimulus - some directions are rewarded.

25. Posterior Parietal Cortex Intra-Parietal Sulcus: area of multi-sensory convergence reaching LIP: Lateral Intra-parietal Area Target selection for saccades: cells fire before saccade to attended object grasping Visual stability

26. Supplementary eye fields: SEF -Saccades/smooth pursuit -Planning/ Error checking -relates to behavioral goals FEF: -Voluntary control of saccades. -Selection from multiple targets -Relates to behavioral goals.

27. Pre-motor neurons Trochlear Abducens V Oculomotor nucleus Motor neurons H Motor neurons for the eye muscles are located in the oculomotor nucleus (III), trochlear nucleus (IV), and abducens nucleus (VI), and reach the extraocular muscles via the corresponding nerves (n. III, n. IV, n. VI). Premotor neurons for controlling eye movements are located in the paramedianpontine reticular formation (PPRF), the mesencephalic reticular formation (MRF), rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), the interstitial nucleus of Cajal (IC), the vestibular nuclei (VN), and the nucleus prepositushypoglossi (NPH).

28. Pulse-Step signal for a saccade

29. Brain areas involved in making a saccadic eye movement Behavioral goal: make a sandwich (learn how to make sandwiches) Frontal cortex. Sub-goal: get peanut butter (secondary reward signal - dopamine - basal ganglia) Visual search for pb: requires memory for eg color of pb or location (memory for visual properties - Inferotemporal cortex; activation of color - V1, V4) Visual search provides saccade goal. LIP - target selection, also FEF Plan saccade - FEF, SEF Coordinate with hands/head Execute saccade/ control time of execution: basal ganglia (substantia nigra pars reticulata, caudate) Calculate velocity/position signal oculomotor nuclei Cerebellum?

30. Relation between saccades and attention. Saccade is always preceded by an attentional shift However, attention can be allocated covertly to the peripheral retina without a saccade. Pursuit movements also require attention.

31. Superior colliculus

32. Brain Circuitry for Pursuit Smooth pursuit & Supplementary Velocity signal Early motion analysis

33. Gaze shifts: eye plus head

36. Visual Stability Efference copy or corollary discharge

37. Figure 8.18 The comparator

44. Brainstem circuits for saccades. Omnipauseneurons (OPN) in the nucleus raphe interpositus (RIP) tonically inhibit excitatory burst neurons (EBN) located in the paramedianpontinereticular formation (PPRF). When OPNs pause, the EBNs emit a burst of spikes, which activate motor neurons (MN) in the abducens nucleus (VI) innervating the lateral rectus muscle. The burst also activates interneurons (IN) whichactivate motor neurons on the oculomotornucleus (III) on the opposite side, innervating the medial rectus. Inhibitory burst neurons (IBN) show a pattern of activity similar to EBNs, but provide inhibitory inputs to decrease activation in the complementary circuits and antagonist muscles. Long-lead burst neurons (LLBN) show activity long before movement onset, and provide an excitatory input to EBNs.

46. RF reticular formation VN vestibular nucle PN , pontinenucleii Cerebellum OV oculomotorvermis VPF ventral paraflocculus FN fastigial nucleus