Foveal gaze shifts

saccades

• very fast, yoked eye movements

• produce quick phase of VOR & OKN

• reflexively shift gaze in response to novel stimuli

• shift gaze during reading

• search novel scenes

• return gaze to remembered spatial locations

• move the eye rapidly from one position to another & maintain the new eye position

pulse

lots of fast action potentials that generate a large, brief force to start the saccade

step

sustained action potentials to generate a tonic level of force to maintain the new eye position

pulse & step

what 2 neuron firing components make up a saccade?

nucleus prepositus hypoglossi (NPH)

• neural integration for horizontal saccades

• calculates the rate of the step needed to hold the eyes at an eccentric location to balance the pulse that moved the eyes

glissadic overshoot

pulse is larger than the integration, eye moved too far then slides back into the correct position

glissadic undershoot

the eye did not move far enough, had to go a bit further to get into the correct position

glissade

post-saccadic drift

main sequence

systematic relationship between magnitude of eye movement & peak velocity

dysmetria

abnormal saccade amplitudes

motor efference copy sent to cerebellum

how are saccades able to use feedback?

no

are saccades ballistic?

accommodation, convergence, pupil constriction

what are the 3 components in convergence/disconjugate shifts of gaze distance

increases

vergence velocity ______ when accompanied by a saccade

FEF/SC, PPRF/riMLF

describe the neural network for saccades

PPRF

brain area for horizontal saccades

riMLF

brain area for vertical saccades

medium lead burst cells

neurons that control the pulse component of a saccade

long lead burst cells

neurons that discharge up to 200ms before the saccade & receive input from the SC & FEF & drive medium-lead burst cells for saccades

inhibitory burst cells

neurons that inhibit antagonist muscles by suppressing neurons in the contralateral abducens nucleus for saccades

omnipause neurons

neurons that normally prevent saccades by inhibiting burst cells; discharge continuously except immediately before & during the actual saccade

tonic cell

neuron that holds the new eye position after a saccade with the discharge step

medial vestibular nuclei & nucleus prepositus hypoglossi

2 neural locations known to integrate horizontal pulses & code for the step portion of a saccade

interstitial nucleus of cajal

neural location for the integration of vertical saccades

180-200ms

time of a normal saccade

100-150ms

time of a corrective saccade

<100ms

time of an express saccade

accommodative convergence

done with monocular occlusion; increases linearly with changes in accommodation stimulated by blur

convergence accommodation

done with binocular viewing through pinhole pupils; increases linearly with changes in convergence stimulated by disparity

1sec

vergence & accommodation response time

vergence, latency

between vergence & accommodation, _____ is faster because of _____

2x

with a saccade, accommodation occurs ____ faster

5x

with a saccade, vergence occurs ____ faster

polysensory

saccades are said to be _____ (stimulated by visual, auditory, or tactile stimuli)

ipsilateral CN6, contralateral CN3

the PPRF projects to ________

ipsilateral CN4, contralateral & ipsilateral CN3

the riMLF projects to _________

medium-lead burst neurons

what controls the pulse of a saccade?

omnipause neurons

• initiate pulse of saccades

• inhibit all saccades

• pause for actual saccades

• control saccade & vergence bursters

glissadic undershoot

which type of glissade is more common?