Fig. 3.

Changes in the vocal structure of victim screams as a function of the level of aggression experienced and whether or not an individual equal to or outranking the aggressor was in the audience. The mean and standard error values for these six variables are shown. Error bars represent one standard error. Sample sizes are as follows: for occurrences of severe aggression with a high-ranking bystander present, n = 12, and with a high-ranking bystander absent, n = 9; for occurrences of mild aggression with a high-ranking bystander present, n = 10, and with a high-ranking bystander absent, n = 11.