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

1. Eye movements and visual stability Kandel et al Ch 29, end of Wolfe Ch 8 KandelCh 39 for more info. Advanced: Werner & ChalupaCh 63

2. Why do we move our eyes? - Image stabilization - Information acquisition Bring objects of interest onto high acuity region in fovea.

3. Visual Acuity matches photoreceptor density

4. 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

5. 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

6. 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.

7. Acuity – babies Rotational or translational Acceleration Depth-dependent gain, Precision in natural vision Velocity Ocular following - Miles

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

9. The vestibular labyrinth Rotational (semi-circular canals) translational (otoliths)

10. Hair cell responses

11. Neural pathways for the angular-VOR three-neuron arc Vestibular latency is about 10 - 15 msec

12. Demonstration of VOR and its precision – sitting vs standing

14. 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.

15. “main sequence”: duration = c Amplitude + b (also V = a Amp+d) Min saccade duration approx 25 msec, max approx 200msec

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

17. 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/

18. Brain Circuitry for Saccades 1. Neural activity related to saccade 2. Microstimulation generates saccade 3. Lesions impair saccade monitor/plan movements Dorso-lateral pre-frontal (memory) V Basal ganglia H Oculomotor nuclei

20. 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

21. FEF – visual, visuo-motor, and movement cells

22. 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.

23. 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.

24. Superior colliculus

25. 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).

26. Pulse-Step signal for a saccade

27. 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?

28. 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.

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

30. Gaze shifts: eye plus head

32. Visual Stability Efference copy or corollary discharge

33. Figure 8.18 The comparator

34. Experiments with partial and complete paralysis of extra-ocular muscles Stevens et al – partial paralysis – world jumps during an em Matin – complete paralysis – no motion Resolution: Bayesian cue combination.

40. Note: Visual stability vs Visual Direction Constancy