Context-specific adaptation of pursuit initiation in humans

PURPOSE. To determine if multiple states for the initiation of pursuit, as assessed by acceleration in the "open-loop" period, can be learned and gate d by context. METHODS. Four normal subjects were studied. A modified step-ramp paradigm f or horizontal pursuit was used to induce adaptation. In an increasing parad igm, target velocity doubled 230 msec after onset; in a decreasing paradigm , it was halved. In the first experiment, vertical eye position (+/-5 degre es) was used as the context cue, and the training paradigm (increasing or d ecreasing) changed with vertical eye position. In the second experiment, wi th vertical position constant, when the target was red, training was decrea sing, and when green, increasing. The average eye acceleration in the first 100 msec of tracking was the index of open-loop pursuit performance. RESULTS; With vertical position as the cue, pursuit adaptation differed bet ween up and down gaze. In some cases, the direction of adaptation was in ex act accord with the training stimuli. In others, acceleration increased or decreased for both up and down gaze but always in correct relative proporti on to the training stimuli. In contrast, multiple adaptive states were not induced with color as the cue. CONCLUSIONS. Multiple values for the relationship between the average eye a cceleration during the initiation of pursuit and target velocity could be l earned and gated by context. Vertical position was an effective contextual cue but not target color, implying that useful contextual cues must be simi lar to those occurring naturally, for example, orbital position with eye mu scle weakness.