Can substitution explain crowding? A study of error distribution in letter crowding
Leo Cheung, Cheung Sing-hang · 2015
Crowding severely limits the identification of a flanked target in peripheral vision. When the object is a letter, crowding could result in letter confusion. One explanation for crowding is that flankers substitute the target. We hypothesized that crowding would alter the error distribution which could be represented by a Letter Confusion matrix (LCM). Comparing the LCMs of unflanked intact, unflanked degraded, letter-flanked and number-flanked conditions, we found that substitution could partially explain the difference in error dispersion between letter- and number-flanked conditions, but not the seeming similarity in error dispersion between number-flanked and unflanked intact conditions. Compared with such conventional measures of visual crowding as recognition accuracy and contrast threshold elevation, error dispersion in LCMs appears to be more specific to a particular type of crowding, for example, when flanker substitution is or is not possible; in addition, LCMs can distinguish between visual crowding and other types of deterioration in visual signal.