Divided Attention in American Sign Language Processing

Previous work investigating simultaneous judgments of multiple stimuli in visual tasks has revealed a range of divided attention effects. There appears to be no capacity limit for simple tasks, such as judging the color of two stimuli simultaneously relative to judging one (White et al., 2018). In contrast, there are pronounced deficits in performance when judging two words simultaneously (White et al., 2018; Campbell and White, 2022), indicating a large capacity limit. Divided attention effects for the categorization of nameable objects are intermediate; less severe than for words, but greater than for color (Popovkina et al., 2021; 2023). Here, we investigated divided attention effects for American Sign Language (ASL) for signers and non-signers to test if capacity limits for processing ASL letters are more like written words than for objects, and whether expertise with ASL influences divided attention for signs. Our participants were either fluent with ASL (signers, n=6) or had no ASL knowledge (non-signers, n=7). Participants saw two simultaneously presented ASL letters, and responded whether a probe stimulus matched the stimulus in a previously cued location. In the single-task condition, only one of two stimuli was cued as relevant; in the dual-task condition, both stimuli were cued as relevant. The difference in performance between these two conditions is the dual-task deficit, which quantifies the cost of dividing attention. The dual-task deficit was similar in signers and non-signers (11.2% ± 1.92% vs. 10.72% ± 1.70%), with no significant difference between the groups (t(11) = 0.19, p = 0.85). The magnitude of the divided attention effect for ASL letters was smaller than those for written word judgments, but similar to those for nameable object judgments. These results suggest that ASL letter processing has limited capacity, but the underlying source of that limit may be different than for written words.