Rich in modality, poor in value? Understanding the impact of multimodality on review helpfulness

While multimodal information has been widely recognized for its synergistic benefits in supporting consumer decision-making, its potential negative effects on information evaluation have been largely overlooked. Drawing on online review data from five Southeast Asian e-commerce platforms and grounded in the cognitive theory of multimedia learning, this study investigates the impact of multimodality on review helpfulness and provides empirical evidence for the plausibility of antagonistic effects. The results reveal two distinct nonlinear pathways through which multimodality indirectly influences the effect of review text length on helpfulness. Under unimodality without visual stimuli and bimodality combining text with a single visual modality, text length exhibits a nonlinear positive relationship with helpfulness, characterized by diminishing marginal returns. Under trimodality involving both image and video stimuli, the diminishing returns reverse the previously positive relationship, resulting in an inverted U-shaped curve. In addition, a direct effect of multimodality is identified: bimodality exerts a significantly stronger positive effect on review helpfulness than both unimodality and trimodality. Further analysis shows no significant difference in helpfulness between text–image and text–video combinations within the bimodal condition. These findings challenge the prevailing view that the inclusion of more modalities necessarily enhances review helpfulness and suggest that complex visual stimuli may not always yield more favorable outcomes, thereby enriching the theoretical understanding of multimodality and offering practical implications for optimizing information services.