An important merit of my working model is that it leaves completely open what type of explanation to use for the direction of lateral difference. In particular, the model will accommodate explanatory factors over and above hemispheric asymmetry by itself. For I have found that telephoning habits (though a monaural activity) have an influence upon the right speech advantage. This may work through biasing the direction of attention, but the group right advantage remains significant when attention is controlled experimentally (Neuropsychologia 20).
Though in the 1980s there was still uncertainty over whether more people do use the right ear for telephoning, the advent of the mobile phone has made this easier to check observationally; there does appear to be a substantial right preponderance (but see this PDF for more discussion). Other environmental factors, many of them deriving from the majority tendency to prefer the right hand, may also influence the right speech advantage. These factors will need to be understood and monitored to improve the utility of using speech side advantage as a soft neurological indicator of cerebral dominance.
A methodological development that may permit readier laboratory demonstration of right speech advantage is my use of group testing (participants placed in between loudspeakers rather than wearing headphones) – Cortex 22 319-324. This is why the advantage is better described as one of side rather than one of ear.