Guiding Task Choice in Japanese Voice Interfaces through Vocalization Cost: Click-based vs. Voice-based Selection

Intrinsic motivation is known to improve task performance when individuals make their own choices. However, when multiple tasks are available, people often choose easier ones even when more difficult or troublesome tasks may be more beneficial. This study investigates whether the phrasing of spoken options can influence such decisions in Voice-based interfaces by leveraging the cognitive and articulatory effort required for vocalization. We conducted a controlled experiment with 40 participants, systematically varying the linguistic complexity of Japanese adverbial phrases in a pointing task and comparing Voice-based and Click-based selection. Results indicated a clear tendency in the voice condition to avoid the most complex phrase and revealed a modality-specific positional tendency in which left-positioned options were chosen more often and right-positioned options were avoided. To our knowledge, this is the first empirical study to demonstrate that vocalization cost can systematically bias task selection in Japanese voice interfaces. These findings suggest that carefully designed spoken language can subtly guide task selection, providing implications for fair and effective voice interface design.