Crowding is the inability to distinguish an outlying object because of its close proximity to other things (flankers). This syndrome, linked to macular degeneration, amblyopia, and dyslexia, causes reading and object identification difficulties. Importantly, the maximum target-flanker distance (critical spacing) that is necessary for crowding interference grows with eccentricity. 

Additionally, the spacing is greater when the target and flankers are arranged radially (along the horizontal meridian) than when the flankers are above and below the target (tangential arrangement). Radial-tangential anisotropy is the name given to the phenomenon. In prior research, transient attention has been shown to lessen crowding interference, but it was unknown whether and how attention interacts with radial-tangential anisotropy. Researchers used cues at either the target (valid) or the fixation (neutral) position, in both radial and tangential target-flanker combinations, to modulate transient attention to overcome the problem. 

According to the results, the critical spacing was bigger in the radial arrangement than in the tangential design, and cueing the target position increased performance and decreased the critical spacing for both configurations to an equal level. 

The research suggested that crowding did not depend on transitory spatial attention although radial-tangential anisotropy did.

Reference: jov.arvojournals.org/article.aspx?articleid=2783537