Understanding a person's ability to communicate with devices or people in their environment requires extensive consideration of language. For the purposes of product design, communication is assumed to be the capability to understand or express simple sentences in speech or text. This is primarily a result of thinking in general, and in particular verbal thinking. It also involves visual thinking, memory, attention, vision and hearing.

A product interface makes a communication demand on the user. Text and speech can describe what controls do, provide feedback, issue warnings or commands, and provide detailed instructions. Usability is therefore dependent on the capability to

• Perceive and understand written words and sentences on their own or in the context of a more complex environment
• Perceive and understand spoken words and sentences in both quiet and noisy environments

Educational levels and social skills will influence a person's communication ability, and therefore affect product interaction.