Ship or boat?

As an example: 'One of my PhD researchers is carrying out experiments with conflict situations which you might come across if you are involved in language production. Sometimes there are several words available for the same concept. For example 'ship' and 'boat'. Sometimes ship and boat mean something completely different, but often they are synonyms. One person might always say 'ship' and another 'boat'. We divided our research subjects into two groups: those who always say 'boat' and those who always say 'ship'. We then divided these groups into a further two groups. In an MRI scanner we showed the candidates pictures of different vessels. One group was allowed to say what they would normally say, but the other was instructed to say 'boat' when they would normally say 'ship', and vice versa. We had expected some internal conflict with the last group since they were having to suppress something. Indeed, we demonstrated that the area of the brain which is responsible for cognitive control was more active in this group.'