Two research groups at Harvard Computer Science focus primarily on Human-Computer Interaction:

• The Glassman Lab led by Elena Glassman
• The Intelligent Interactive Systems Group led by Krzysztof Gajos 

There are also several other faculty members (and groups) throughout Harvard that do HCI-related research at least part of the time:

• Karen Brennan
• Hanspeter Pfister
• Bertrand Schneider