ECVP 2006

Non-retinotopic crowding

Patrick Cavanagh

Alex O Holcombe

The movies below show you the stimuli used in our crowding experiments. Click here to open the abstract in a separate window. The alternation rate in our demonstration is quite low (3 Hz) so the crowding you see in the first movie may not be very pronounced (this depends on the individual). The experiments showed that the strongest crowding is seen at higher rates (4 to 5 Hz or higher). In the first movie, you should fixate the center and attend to one location (our subjects attended to the bottom location) and report whether the target (3rd letter down) is a normal or left-right reversed letter (reversed here). Notice that the target on each arm is different but they all have the same version (all reversed here) so that even if you notice a different target, you will have the right answer. Click on the play button on the bottom left to start the movie.

 

Next we add a guide that jumps from location to location, timed so that it lands on each arm when only the target is there. In addition, we move the whole array one position on each frame so the same letter is present all the time where you are attending. Fixate again and follow the light sector with attention as it moves, noticing whether the target is normal or left-right reversed (reversed here). If you are like our subjects, you may find this moving target easier to see than the stationary one, suggesting that crowding is non-retinotopic: it depends on the flankers that move with the target, not those that surround it in retintopic coordinates.