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Steady-State Pursuit Is Driven by Object Motion Rather Than the Vector Average of Local MotionsWe have previously shown that humans can pursue the motion of objects whose trajectories can be recovered only by spatio-temporal integration of local motion signals. We now explore the integration rule used to derive the target-motion signal driving pursuit. We measured the pursuit response of 4 observers (2 naive) to the motion of a line-figure diamond viewed through two vertical bar apertures (0.2 cd/square m). The comers were always occluded so that only four line segments (93 cd/square m) were visible behind the occluding foreground (38 cd/square m). The diamond was flattened (40 & 140 degree vertex angles) such that vector averaging of the local normal motions and vertical integration (e.g. IOC) yield very I or different predictions, analogous to using a Type II plaid. The diamond moved along Lissajous-figure trajectories (Ax = Ay = 2 degrees; TFx = 0.8 Hz; TFy = 0.4 Hz). We presented only 1.25 cycles and used 6 different randomly interleaved initial relative phases to minimize the role of predictive strategies. Observers were instructed to track the diamond and reported that its motion was always coherent (unlike type II plaids). Saccade-free portions of the horizontal and vertical eye-position traces sampled at 240 Hz were fit by separate sinusoids. Pursuit gain with respect to the diamond averaged 0.7 across subjects and directions. The ratio of the mean vertical to horizontal amplitude of the pursuit response was 1.7 +/- 0.7 averaged across subjects (1SD). This is close to the prediction of 1.0 from vertical motion-integration rules, but far from 7.7 predicted by vector averaging and infinity predicted by segment- or terminator-tracking strategies. Because there is no retinal motion which directly corresponds to the diamond's motion, steady-state pursuit of our "virtual" diamond is not closed-loop in the traditional sense. Thus, accurate pursuit is unlikely to result simply from local retinal negative feedback. We conclude that the signal driving steady-state pursuit is not the vector average of local motion signals, but rather a more vertical estimate of object motion, derived in extrastriate cortical areas beyond V1, perhaps NIT or MST.
Document ID
20020042330
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Stone, Leland S.
(NASA Ames Research Center Moffett Field, CA United States)
Beutter, B. R.
(NASA Ames Research Center Moffett Field, CA United States)
Lorenceau, J. D.
(College de France Paris, France)
Ahumada, Al
Date Acquired
August 20, 2013
Publication Date
January 1, 1997
Subject Category
Behavioral Sciences
Meeting Information
Meeting: 1997 Annual Meeting of the Association for Research in Vision and Opthalmology
Location: Fort Lauderdale, FL
Country: United States
Start Date: May 11, 1997
End Date: May 16, 1997
Sponsors: Association for Research in Vision and Opthalmology
Funding Number(s)
PROJECT: RTOP 548-50-12
PROJECT: RTOP 199-16-12-37
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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