Mobile Computation

When stimuli move rapidly over the retina, analyses at each location may not have time to reach completion before the stimulus moves on. Using apparent motion, we found nonretinotopic accumulation of some object properties (colour and motion) but not others (letter and digit identity). We suggest that this integration is mediated by large receptive fields gated by attention and that it occurs for surface features (motion and colour) that can be summed without precise alignment but not for shape features (letters or digits) that require such alignment. Our results also suggest that as attention moves, the selection of any given location (dwell time) can be as short as 50 ms, far shorter than the typical dwell time for stationary attention. Moving attention can therefore sample a brief instant of a rapidly changing stream if it passes quickly through, giving access to events that are otherwise not seen.

Perception on the fly

Here is an example for a green colour afterimage, normally sandwiched between the successive purple disks at each location and hard to see. On the left, while looking at the centre, there are just a lot of flickering purple disks. It is not evident that there is a green afterimage in the brief moment of time between each successive purple disk. On the right, again while looking at the centre, follow the moving white outline circle. Now attention is visiting each location briefly, and only during the time when the afterimage is present, leaving the location before the next purple disk shows up. This isolates the afterimages, allowing them to be seen immediately — unlike the related magenta chaser display of long ago, there appears to be no delay required for a build up. The article presents the integration of properties like motion and colour across these separate locations (Cavanagh, Holcombe, & Chou, 2008, PDF).