This project addresses two types of eye movement (saccades, OKN), with emphasis on timing in response to visual stimuli. Saccades are rapid movements made when scanning a visual scene. Saccades to periodically-paced targets have a characteristic latency: as pacing rate increases saccades become more anticipatory. OKN (optokinetic nystagmus) occurs with wide-field motion of a scene, and is an indicator of vestibular and oculomotor function. During OKN, the eyes track the field, and intermittently reset their position by moving rapidly in the opposite direction. The eye position waveform looks like a fluctuating sawtooth. OKN is not periodic; models typically rely on statistical characterization of the variations, and recent work indicates that the dominance of random vs. deterministic dynamics makes this reasonable. If a subject actively follows the scene (""""""""look nystagmus""""""""), OKN is different from when a subject simply stares straight ahead (""""""""stare nystagmus""""""""). This may reflect different degrees of reflexive and volitional control. In the first sub-project, scaling properties of periodically-paced saccades will be studied. Many systems have a characteristic scaling behavior, such that variability increases as a power-law function of sequence length, reflecting a type of statistical long-term memory. Scaling of saccade latencies will be assessed with a parametric procedure, and verified graphically. The goal is to assess scaling over the range where saccades are reactive or predictive (latencies positive or negative, respectively). Evidence is that scaling behavior in the predictive regime is different from that in the non-predictive (""""""""reactive"""""""") regime. This relationship can link reflexive/volitional behaviors to predictive/reactive behaviors. Evidence is also presented for altered scaling in cerebellar patients. The second sub-project will apply similar analyses to OKN fast-phase intervals. Evidence indicates that scaling is altered depending on the degree of volitional vs. reflexive behavior. This volitional/reflexive mix can be altered through stimulation of different types of OKN (horizontal vs. torsional, """"""""look"""""""" vs. """"""""stare""""""""), and used to verify the relationship of scaling to behavior. The results will be widely applicable to physiologic systems that can be described by statistical scaling laws, and to systems which exhibit combinations of reflexive and volitional behavior and prediction. Since scaling changes with pathology, new means to assess vestibular or oculomotor pathology may result.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Small Research Grants (R03)
Project #
5R03EY015193-03
Application #
7032970
Study Section
Special Emphasis Panel (ZEY1-VSN (01))
Program Officer
Hunter, Chyren
Project Start
2004-03-01
Project End
2007-02-28
Budget Start
2006-03-01
Budget End
2007-02-28
Support Year
3
Fiscal Year
2006
Total Cost
$159,658
Indirect Cost
Name
Johns Hopkins University
Department
Otolaryngology
Type
Schools of Medicine
DUNS #
001910777
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Joiner, Wilsaan M; Shelhamer, Mark (2009) A model of time estimation and error feedback in predictive timing behavior. J Comput Neurosci 26:119-38
Joiner, Wilsaan M; Lee, Jung-Eun; Lasker, Adrian et al. (2007) An internal clock for predictive saccades is established identically by auditory or visual information. Vision Res 47:1645-54
Zorn, Andrew; Joiner, Wilsaan M; Lasker, Adrian G et al. (2007) Sensory versus motor information in the control of predictive saccade timing. Exp Brain Res 179:505-15
Joiner, Wilsaan M; Lee, Jung-Eun; Shelhamer, Mark (2007) Behavioral analysis of predictive saccade tracking as studied by countermanding. Exp Brain Res 181:307-20
Joiner, Wilsaan M; Shelhamer, Mark (2006) Responses to noisy periodic stimuli reveal properties of a neural predictor. J Neurophysiol 96:2121-6
Joiner, Wilsaan M; Shelhamer, Mark (2006) An internal clock generates repetitive predictive saccades. Exp Brain Res 175:305-20
Joiner, Wilsaan M; Shelhamer, Mark (2006) Pursuit and saccadic tracking exhibit a similar dependence on movement preparation time. Exp Brain Res 173:572-86
Joiner, Wilsaan M; Shelhamer, Mark; Ying, Sarah H (2005) Cerebellar influence in oculomotor phase-transition behavior. Ann N Y Acad Sci 1039:536-9
Shelhamer, Mark (2005) Sequences of predictive eye movements form a fractional Brownian series--implications for self-organized criticality in the oculomotor system. Biol Cybern 93:43-53
Shelhamer, Mark (2005) Sequences of predictive saccades are correlated over a span of approximately 2 s and produce a fractal time series. J Neurophysiol 93:2002-11