Tenta assim Fernando,

segplot(reorder(tratamento, media)~inferior+superior|fator, data=dados,
        centers=media, draw.bands=FALSE, segments.fun=panel.arrows,
        ends='both', angle=90, length=1, unit='mm',
        panel=function(x, y, z, centers, subscripts, ...) {
            wp <- which.packet()
            panel.rect(dadosAUX[wp,"xleft"], min(as.numeric(z))-1,
                       dadosAUX[wp,"xright"], max(as.numeric(z))+1,
                       fill=rgb(0.5,0.5,0.5,0.7), border=FALSE)
            panel.segplot(x, y, z, centers=centers, subscripts=subscripts, ...)
        })

À disposição.
Walmes.