Single-letter (but not multi-letter) flankers produce a leftward asymmetry in the flanker lexical decision task

We conducted three flanker lexical decision experiments to test whether multi-letter and single-letter flankers to the left and right of a target word produce symmetrical facilitation relative to an unrelated control. We also simulated these experiments using the PONG model (Snell, J. (2025). PONG: A computational model of visual word recognition through bihemispheric activation. Psychological Review, 132(3), 505–527), a model that provides quantitative predictions for this task. In Experiment 1 we found symmetrical facilitation from left-consistent and right-consistent bigrams. In contrast, Experiments 2 and 3, using single-letter flankers, revealed leftward benefits, even when the consonant–vowel distribution of the flanker letters was balanced (Experiment 3). The PONG model quantitatively captured the pattern in Experiment 1 but failed to capture the leftward advantage in Experiments 2–3. This dissociation reveals that parafoveal information during visual word recognition is hemifield-symmetric for multi-letter chunks but left-weighted for single letters, suggesting that models of visual word recognition require initial-letter or hemifield weighting to account for single-letter flanker effects.本研究开展了三项侧翼范式词汇判断实验（flanker lexical decision experiment），以检验目标词左右两侧的多字母侧翼刺激与单字母侧翼刺激，是否会相对于无关控制条件产生对称的易化效应。本研究同时采用PONG模型（PONG model）对上述实验进行模拟，该模型源自Snell J.于2025年发表的研究《PONG：基于双半球激活的视觉词汇识别计算模型》（《心理评论》, 132(3), 505–527），可为该任务提供量化预测。实验1结果显示，左侧一致性双字母组（bigram）与右侧一致性双字母组均可引发对称易化效应。与之相对，使用单字母侧翼刺激的实验2与实验3则呈现出左侧优势效应，即便侧翼字母的辅音-元音分布已实现平衡（实验3），该效应依然存在。PONG模型可定量复现实验1的结果，但无法解释实验2至实验3中的左侧优势效应。这一分离效应表明，视觉词汇识别过程中的副中央凹信息（parafoveal information），对多字母组块呈现半视野对称的加工模式，而对单字母刺激则呈现左侧加权的加工模式，这提示视觉词汇识别模型需引入首字母或半视野加权机制，以解释单字母侧翼效应。