Abstract
How features are integrated into a unique percept is one of the most puzzling questions in visual neuroscience. According to Feature Integration Theory, features are bound together by attention. In recent years, a variety of studies has shown that features of moving objects are integrated along their motion trajectories and, hence, across different retinotopic locations. For example, we presented a central Vernier that was slightly offset either to the left or right. On either side of this central Vernier, a sequence of non-offset flanking lines followed eliciting a percept of two diverging motion streams. Although the Vernier itself was largely invisible in this sequential metacontrast paradigm, surprisingly, its offset was perceived within the motion streams. If one of the flanking lines was offset itself, this offset was integrated with the offset of the Vernier. To investigate the role of attention in this non-retinotopic feature integration, an auditory cue was presented indicating to which of the two motion streams observers had to attend. The timing of the cue-onset was systematically varied from 500 ms before stimulus onset to 300 ms after its offset. Interestingly, non-retinotopic feature integration occurred even in conditions when the cue was presented 300 ms after the offset of the motion streams. This finding suggests that non-retinotopic feature integration is mediated by pre-attentive motion grouping and not by attention.
T.U. Otto was supported by the Swiss National Science Foundation.