This paper is a manually-entered copy of the complete published text of the 1979paper. The author thanks the editors of erstwhile Perceptual and Motor Skillsfor thisspecial permission. The published text pagination has been preserver, except thathyphenated words and REFERENCES crossing page boundaries have been gathered tothe page on which they were begun.In addition to this Preface, one minor change has been made to correct a newly-founderror on the published p. 518, an error which is explained the