Adaptation to spiral motion: global but not local motion detectors are modulated by attention.

In this study, we investigated the effect of attention on local motion detectors. For this purpose we used logarithmic spirals previously used by Cavanagh and Favreau [Perception, 1980, 9(2), 175-182]. While the adapting stimulus was a rotating logarithmic spiral, the test stimulus was either the same spiral or its mirror image. When superimposed, all contours of the spiral stimulus and its mirror image are 90 degrees apart. Presenting the same spiral during the test period shows adaptation of both local motion detectors and global rotation detectors, whereas showing the mirror-spiral stimulates another set of local motion detectors, and therefore illustrates adaptation at only the global motion level. To manipulate the attentional state of observers, a secondary task was presented during the adaptation phase and observers either performed the task or ignored it. Motion aftereffect (MAE) duration was measured afterwards. While the effects of attention and test stimulus type on MAE duration were both significant, the difference in the MAE strength between the attention-distracted and attention-not-distracted conditions was equal when the test stimulus was the same-spiral or the mirror-spiral, suggesting that attention to spiral motion modulates only global rotation units and does not affect local motion detectors located at V1. Our results are in accord with those reported by Watanabe et al. [Proceedings of the National Academy of Sciences of the USA, 1998, 95(19), 11489-11492] which showed differential modulation of motion processing areas depending on the type of motion being attended. Therefore our data are supportive of the notion that attentional modulation of V1 is highly task-dependent.