Ocular pursuit responses to repeated, single-cycle sinusoids reveal behavior compatible with predictive pursuit

The link between anticipatory smooth eye movements and prediction in sinuso idal pursuit was investigated by presentation of series of identical, singl e-cycle, sinusoidal target motion stimuli. Stimuli occurred at randomized i ntervals (1.2-2.8 s) but were preceded by an audio warning cue 480 ms befor e each presentation. Cycle period (T) varied from 0.64 to 2.56 s and target displacement from 4 to 20 degrees in separate series. For T less than or e qual to 1.28 s, responses to the first stimulus of each series exhibited a time delay across the whole cycle (mean = 121 ms for T = 0.8 s). But, in th e second and subsequent (steady-state) presentations, anticipatory movement s, proportional to target velocity, were made and time delay was significan tly reduced (mean = 43 ms for T = 0.8 s). Steady-state time delays were com parable to those evoked during continuous sinusoidal pursuit and less than pursuit reaction time. Even when subjects did not follow the target in the first presentation, they responded to the second presentation with reduced time delay. Throughout the experiments, three types of catch trial (A-C) we re introduced. In A, the target failed to appear as expected after the warn ing cue. Anticipatory smooth movements were initiated, reaching a peak velo city proportional to prior target velocity around 200 ms after expected tar get onset. In B, the target stopped midway through the cycle. Even if the t arget remained on and was stationary, the eye movement continued to be driv en away from the stationary target with a velocity similar to that of prior responses, reaching a peak velocity that was again proportional to expecte d target velocity after greater than or equal to 205 ms. In C, the amplitud e of the single sinusoid was unexpectedly increased or decreased. When it d ecreased, eye velocity throughout the first half-cycle of the response was close to that executed in response to prior stimuli of higher velocity and did not return to an appropriate level for 382-549 ms. Conversely, when amp litude increased, eye velocity remained inappropriately low for the first h alf-cycle. Results of A and C indicate that subjects are able to use veloci ty information stored from prior presentations to initiate an oculomotor dr ive that predominates over visual feedback for the first half-cycle. Result s of B indicate that the second part of the cycle is also preprogrammed bec ause it continued despite efforts to suppress it by fixation. The results s uggest that initial retinal velocity error information can be sampled, stor ed, and subsequently replayed as a bi-directional anticipatory pattern of m ovement that reduces temporal delay and could account for predictive contro l during sinusoidal pursuit.