Today the HRI community generates a lot of knowledge on how one robot affects one human, and how one robot affects multiple human listeners. Much less knowledge is available on how robots affect the human language and how this language change can affect human attitudes and behaviours. This language effect is of particular interest for when we get into a situation where a major part of the human population has robots, as we are now experiencing with the ubiquity of smartphones. In this case, the questions are: What happens if all robots were to use the same words? For example, when they all use the same source as their dictionary. Will robots be able to affect the word choices of the human population, and what are the implications of connotation-laden vocabulary? Even more interesting, will this word choice affect the attitudes and behaviours of the human population?

Through all those questions a central question for this thesis emerged: "Are Robots able to influence a group of people via the usage of language?" To find out if this might be possible, we developed three connected experiments. In the first, the effect of peer pressure on humans created by robots is explored, focusing on how this peer pressure affects the language of a person. To see if and how this influence of robots works, the effect of the robots was compared against that of human actors. The results of the ex- periment showed that the actors could indeed influence the participants as predicted, however, no such influence could be shown by the robots. It was concluded that the reason the robots did not affect the humans was that the participants did not feel that they belonged to the robots group.

In the second experiment, a robot and human group setting was created. In this experiment, the robot tried to influence the human language. Important here to mention is that the experiment measured if the language of participants was affected by the robot influence, even after the interaction and without any robot in the room. It was also mea- sured if the word chosen by the robot had an influence on how a person would perceive the discussed object. The outcome of the experiment was successful, and showed that the group building worked and the robot was able to affect the human language, even after the interaction was over. It further showed that robots were able to affect the hu- mans attitude toward objects simply by using positive or negative connoted synonyms for a particular object.

In the third and last experiment, the question was: Can many robots affect the language of a whole human population? To answer this, different parameters were measured: How many humans need robots so that the robots could manipulate the whole human populations language? And does it matter which persons in the human population will get a robot - whether it be a person who is very well connected or a person who is poorly connected, for example? Since we are currently not in a time where a huge number of people actually have robots, a simulation was created. The outcome of the simulation was that on average only 11% of the human population needed robots to affect the language of 95% of the human population.

Finally, to further deepen the knowledge on how simple language change can affect human attitude and behaviour a literature review is added. This review focuses particularly on persuasion via language, which includes effects like gender neutral versus non-gender neutral language.

The conclusion of this thesis is that in certain situations, a group of robots is able to affect the language, and in turn the behavioural responses, of the majority of the human population.