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The strong early reflections and short delay times have been known to improve intelligibility of speech heard in rooms. D50 and C80, the most frequently used physical parameters were developed considering this fact. However, these monaural parameters have limited applications for the practical design of rooms because of their lack of spatial information. The present work investigates how temporal changes in three-dimensional distribution of early reflections influence speech intelligibility in rooms. A new measurement method, using a five microphones array and an omni-directional source setup, is employed, and a series of post-processing procedures are involved for getting different early reflections in their spatial distributions. The changes were made for the impulse responses, obtained through a five microphones array in the arrival times of early reflections from the all, horizontal, and vertical direction, respectively. Anechoic samples of Korean language were convolved binaurally with the reproduced impulses by applying a head-related transfer function. A series of speech intelligibility test, conducted for 32 university students, found that the percentage of correct responses were significantly deteriorated by increasing delay times of early reflections from the vertical direction. The result suggests that vertical components of early reflections play a significant role in improving speech intelligibility.