From: http://www.ncbi.nlm.nih.gov/pubmed/19417224

"The present review examines and summarizes the current knowledge of factors affecting the freely chosen cadence during submaximal cycling and of the influence of cadence choice on performance. [...] A number of factors, including age, power output, and road gradient, have been shown to affect the choice of cadence to some extent. During high-intensity cycling, close to the maximal aerobic power output, cyclists choose an energetically economical cadence that is also favorable for performance. In contrast, the choice of a relatively high cadence during cycling at low-to-moderate intensity is uneconomical and could compromise performance during prolonged cycling." (emphasis added)

[Edit:] And, let's remember that the OP is new to road cycling. Here's a study of non-cyclists that would be appropriate for beginners: http://www.ncbi.nlm.nih.gov/pubmed/19430807

"The purpose of this study was to examine both the freely chosen cadence (FCC) and the physical variables associated with cadence selection in non-cyclists. [...] peripheral ratings of perceived exertion (RPE) were used to measure the most comfortable cadence and the cadence whereby muscle strain was minimised. [...] At 60% W (max), RPE peripheral was minimised at [...] the FCC."

Bottom line from both of these studies: even beginners seem to choose the cadences that minimize their effort and artificially changing that cadence away from the freely-chosen rate increased their perceived effort.