Determining the functional requirements for new software is a significant problem because it is dependent upon effective conversation between software designers and users. Prototypes and scenarios are two key techniques that have been advocated to improve the specification and communication of software requirements. This paper describes experimental research examining the utilization of prototypes and scenarios during designer-user conversation to determine and validate software requirements. This study is among the first to empirically test the effectiveness of employing scenarios in requirements determination. The results indicate that scenarios can affect user feedback in conversation about software requirements. The results also suggest that software designers should present users with a combination of software prototypes alongside abstract, diagrammatic models when discussing software requirements.