Santella, D & Carrasco,
M (2003). Perceptual consequences of temporal disparities in the visual
field: The case of the line motion illusion. Vision Sciences Society.
Background and Goal. When a line is preceded by a cue, it appears to be
drawn from the end where the cue appeared. This is known as the illusory
line motion (Hikosaka, Satoru & Shimojo, 1993). In this study, we characterized
the changes in perception of the illusion over the visual field to explore
whether these changes correspond to temporal performance field asymmetries
-information is processed faster along the horizontal than vertical meridian,
and at the lower than upper vertical meridian (Carrasco, McElree & Giordano,
Method. Twenty observers were presented with a 100 ms line either preceded
(illusion) or not preceded (control) by the cue. The line appeared on
the horizontal and vertical meridians at 4 or 9° eccentricity. In the
'focused attention' condition, the cue appeared only at the location adjacent
to that at which the line would appear. In the 'distributed attention'
condition 4 cues appeared adjacent to all 4 possible locations. Observers
responded in a 3AFC task with either of 2 directions of motion (E vs.
W, or N vs. S) or no motion.
Results and Conclusion. (a) With focused attention, the illusion was more
pronounced along the horizontal than vertical meridian, and least pronounced
at the North location. This pattern of results was consistent with the
temporal performance field asymmetries aforementioned. (b) With distributed
attention, the illusion decreased at all locations to the point that its
magnitude became comparable at all locations. These results are consistent
with the fact that attention speeds information accrual (Carrasco & McElree,
2000) and that attention eliminates temporal asymmetries in the visual
field (Carrasco, Giordano & McElree, VSS 2003). Taken together, these
results clearly illustrate the perceptual consequences of disparities
in the speed of processing at different locations.