The dispersion and deposition characteristics of polydispersed expiratory aerosols were investigated in an aircraft cabin mockup to study the transmission of infectious diseases. The airflow was characterized by particle image velocimetry (PIV) measurements. Aerosol dispersionwas measured by the Interferometric Mie Imaging (IMI) method combined with an aerosol spectrometer. Deposition was investigated using the fluorescent dye technique. Downward air currents were observed near the seats next to the side walls while upward airflows were observed near other seats. The downward airflow showed some effects on suppressing the dispersion of aerosols expelled by the passenger sitting in the window seat. Results show that the cough jet could bring significant amount of aerosols forward to the row of seats ahead of the cougher and the aerosols were then dispersed by the bulk air movements in the lateral direction. The aerosols expelled from a cough took 20-30 s to reach the breathing zones of the passengers seated within two rows from the cougher. Increasing the ventilation rate improved the dilution and reduced the aerosol exposure to passengers seated close to the source, but the aerosol dispersion increased, which heightened the exposure to passengers seated further away. 60-70% of expiratory aerosols in mass were deposited, with significant portions on surfaces close to the source, suggesting that disease transmission risk via indirect contact in addition to airborne risk is possible. The physical transport processes of expiratory aerosols could be used to shed insights on some epidemiological observations on in-flight transmission of certain infectious diseases.