I completed my dissertation in November 2009. Here's the full text PDF for download.

Wilkes, S.F. (2009). The Effects of Communication Modality on Presence, Cognitive Load and Retention in Second Life (Doctoral dissertation, Illinois Institute of Technology, 2009).

ABSTRACT

This thesis reports findings from a study (N = 60) of the impact of three communication modalities (voice only, text only, and voice and text simultaneously) on cognitive load, as measured by subjective reports of mental effort; on learning, as measured by tests of recall and retention; and on perceptions of presence as measured by a Presence Questionnaire (Witmer & Singer, 2005). Based on the results of prior empirical research, it is hypothesized that retention scores will be higher for voice participants and voice-and-text participants than for text-only participants; that cognitive load will be lower for voice participants and higher for text conditions; that voice will contribute to greater perceptions to presence; and that higher perceptions of presence will not correlate with deeper learning. Study results indicate that communication modality significantly effected cognitive load (F (2, 54) = 4.58, p = .01) and retention (F (2, 54) = 3.53, p = .04), and that experience with and time spent in the virtual environment had significant effects on measures of cognitive load, retention, and presence: Significant between-subjects effects were found for cognitive load and time (p = .23), for retention and time (p = .21), and for retention and experience (p = .03).