pairs(), no axis labels/values for upper panel?

Dear all,

I want to draw a graph that contains the scatterplot matrix in the lower panel and coefficients in the upper panel. I used and adapted the example for the function pairs but cannot figure out how to get no values and ticks in the upper panel (the values should only be in the lower panel). The upper panel looks odd to me this way. Any hints?

Thanks in advance
Steffen


Here is an example what the graph looks like:
#############################################
data(mtcars)
panel.cor <- function(a, b, digits=2,  ...)
     {
         
	usr <- par("usr"); on.exit(par(usr))
         par(usr = c(0, 1, 0, 1))
         x<-cbind(a,b)
         x<-na.omit(x)
         n <- nrow(x)
         pp <- c(0.025, 0.975)
         corx <- cor(x,method="s")[1, 2]
         CI<-c(tanh(atanh(corx) + qnorm(pp)/sqrt((n - 3)/1.06)))
         txt1 <- paste("rho =",format(c(corx, 0.123456789), digits=digits)[1])
         txt2<-paste("(",format(c(CI,0.123456789)[1],digits=digits),"; ",format(c(CI,0.123456789)[2],digits=digits),")",sep="")
         txt3<-paste("N =",round(n,0))
         txt <- paste(txt1,"\n","95%KI ",txt2,"\n",txt3, sep="")
         text(0.5, 0.5, txt,cex=.8)
     }
	 
diag.cor<-function(a,b, ...)
    {
        usr <- par("usr"); on.exit(par(usr))
        par(usr = c(0, 1, 0,1))
        rect(0,0,1,1,col="grey")
     }

pairs(mtcars[1:4],upper.panel=panel.cor,diag.panel=diag.cor,label.pos=0.5)
#############################################