To calculate reliability for the data, the second coder analyzed approximately 10% of the data across participants and phases. Point-by-point inter-rater agreement was calculated by dividing the number of agreements (i.e., identified the same symbol combination) by the total number of agreements, disagreements, and omissions. The mean reliability score was 95% (range: 79 – 100%) for the frequency of multi-symbol messages, 95% (range: 75 – 100%) for different multi-symbol messages, 86% (range: 79 – 100%) for the semantic-syntactic categories within multi-symbol messages, and 95% (range: 79 – 100%) for communication modes.