The relationship between feature binding and consciousness: evidence from asynchronous multi-modal stimuli

Processing the various features from different feature maps and modalities in coherent ways requires a dedicated integration mechanism ("the binding problem"). Many authors have related feature binding to conscious awareness but little is known about how tight this relationship really is. We presented subjects with asynchronous audiovisual stimuli and tested whether the two features were integrated. The results show that binding took place up to 350 ms feature-onset asynchronies, suggesting that integration covers a relatively wide temporal window. We also asked subjects to explicitly judge whether the two features would belong to the same or to the different events. Unsurprisingly, synchrony judgments decreased with increasing asynchrony. Most importantly, feature binding was entirely unaffected by conscious experience: features were bound whether they were experienced as occurring together or as belonging to a separate events, suggesting that the conscious experience of unity is not a prerequisite for, or a direct consequence of binding.