In this study, we argue that multimodal presentations should be created in a cognitive-aware manner, especially in a high-load HCI situation where the user task challenges the full capacity of the human cognition. An experiment was conducted to investigate the cognitive effects of modalities, using a high-load task. The performance measurements and subjective reports consistently confirm a significant modality impact on cognitive workload, stress and performance. A relation between modality usage and physiological states was not found, due to the insufficient sensitivity and individual differences of the physiological measurements. The findings of this experiment can be well explained by several modality-related cognitive theories. We further integrate these theories into a suitability prediction model, which can systematically predict how suitable a certain modality usage is for this presentation task. The model demonstrates a possible approach towards cognitive-aware modality plannin...