Forty-four introductory psychology students from Virginia Tech took part in a study concerning manning levels and the perception of crowding and related experiences. A new apparatus was designed and built (an HO-gauge train set) to manipulate manning level, physical constraint (using two different control designs), and cognitive load, variables suggested as important in the perception of crowding. Two methods of manipulating manning level were attempted: 1) changing the task and keeping the number of participants constant, and 2) Changing the number of participants and keeping the task constant. The former was found to be more successful in this study, the latter apparently confounded with the number of participants in the group. Both physical constraint and cognitive load affected the participants' expressed experiences. The results indicate that physical constraint had a more consistent negative impact on subjective experiences than did cognitive load. / Master of Science