Kazushi Maruya¹ (), Miki Uetsuki²; ¹NTT Communication Science Laboratories, ²Aoyama Gakuin University

Crowding in strings impairs letter identification (Whitney & Levi, 2011), but the effect is reduced for letter strings compared to symbol strings (Grainger et al., 2010). In Latin script readers, this reduction occurs only in horizontally oriented letter strings (Vejnović & Zdravković, 2015). In contrast, Japanese readers exhibit this reduction in both vertically and horizontally oriented strings (Uetsuki & Maruya, under review). These differences may reflect variations in reading experience with specific string orientations. This study investigated whether Japanese readers also exhibit crowding reduction for letter strings oriented in unfamiliar directions, such as diagonal strings. Nine native Japanese readers participated in the experiment. Stimuli included three types of letters: English alphabet letters, Japanese katakana letters, and symbols. Each trial began with a fixation point, followed by a target letter displayed for 100 ms, either alone (isolated condition) or flanked by two distractors (crowded condition). Targets appeared at one of three locations: left, lower-left, or below the fixation point, at eccentricities of 1.5 or 7 deg. The letter sizes were 0.44 deg for 1.5-deg eccentricity and 2.1 deg for 7-deg eccentricity, with inter-letter distances of 0.6 deg and 3.0 deg, respectively. Participants identified the target using a two-alternative forced choice task. The crowding effect sizes were calculated as the difference in performance between isolated and crowded conditions for each stimulus type and viewing condition, then averaged across participants. Results showed a crowding reduction even for letter strings oriented in unfamiliar directions under specific conditions, such as 1.5-deg eccentricity with right-diagonal string orientation and targets positioned left or below fixation. However, this reduction was inconsistently observed across conditions and less robust than for familiar (horizontal or vertical) orientations. These findings suggest that crowding reduction depends on reading experience with specific string orientations, highlighting the limited role of familiarity in reading.

Acknowledgements: A part of this work was supported by JSPS KAKENHI Grant Number 20K11927.