## enter the filename here (instead of testdata.txt) datafile = "testdata.txt" x=read.table( datafile ) colnames(x)=c("x","y","size","distance","fittslaw","rt","status") ## select the correc trials only correct = x[,"status"]==1 ## you can calculate the distance in R, although PsyToolkit already did for you distance = sqrt( x[,"x"]^2 + x[,"y"]^2 ) ## copy variables from the matrix in simple variables ## for readability rt = x[,"rt"] size = x[,"size"] ## fitts law r = log2( 2 * distance / size ) ## now plot plot( r ,rt ,col=ifelse(correct,"black","grey"),pch=19, las=1, xlab="log2(2 * Distance/Size)", ylab="Response Time (ms)") ## draw a regression line abline( glm( rt ~ r ) , col="red") ## put a title on the plot title("Fitts's Law") ## report the regression print( summary( glm( rt ~ r )))