Fig. 5A–F Comparison of the eye-hand versus eye-only conditions (task C vs. B; experiment 1). These consecu- tive axial slices correspond to panels C–H of Fig. 4
Fig. 6A–F Comparison of the eye-hand versus eye or hand (task C vs. A and B; experi- ment 1) conditions, showing in- creased activation during co- ordinated eye and hand track- ing tasks. Areas of significance were more activated in the eye and hand condition. Notice also the vermal area activated in B. These consecutive axial slices correspond to B–G of Fig. 4.
To examine activation specifically due to co-ordinated hand movement, we contrasted the eye-hand condition with eyes-alone (task C vs. task B). The hand-movement related areas seen in Fig. 4 were again activated (Fig. 5), which was of course expected in this contrast because of the addition of the hand movement to the common eye tracking. However, the vermal area was also significantly activated (Fig. 5A, B). Thus, despite there being similar eye movement in both tasks, this area was significantly more activated when the hand was used in co-ordination with the eyes.
Finally, contrasting the eye-hand condition against both eye-only and hand-only (task C vs. tasks A and B) activated restricted regions in the cerebellum similar to those observed in hand-only tracking (compare Fig. 6B, C with Fig. 4C, D), with activation of ipsilateral ansi-
form lobule and the vermis. However, in this contrast, there was greatly reduced activation within the posterior cerebellar regions (Fig. 6E, F). Thus, the ansiform and vermal cerebellar areas activated by hand tracking alone were significantly more activated during co-ordinated eye and hand tracking. The paramedian/biventer lobule activity was only marginally more activated in the com- bined eye-hand task than in the hand-only task.
Experiment two. Cerebellar activation during visually guided eye movements
To improve the statistical significance of the activation during ocular tracking, we doubled the number of com- parisons between ocular tracking and fixation. There was