Computer programmers break apart large programs into smaller coherent pieces. Each of these pieces: func-tions, subroutines, modules, or abstract datatypes, is usually a contiguous piece of program text. The experi-ment reported here shows that programmers also rou-tinely break programs into one kind of coherent piece which is not coniguous. When debugging unfamiliar pro-grams programmers use program pieces called slices which are sets of statements related by their flow of data. The statements in a slice are not necessarily textually contiguous, but may be scattered through a program.

Research into the psychology of programming has been mostly related to textual programs. The application of the theory of programming to visual programs could be further supported by empirical evidence. Graphical readership, a skill that cannot be ignored in visual programming, has been little explored; similarly the case with regard to the effect of paradigm shift on novice programmers. Our research addresses some of these issues. This paper presents empirical evidence drawn from our experiments of first year students interacting with graphical programs. Results of these experiments provide support for the match-mismatch hypothesis, a control flow bias among novice programmers, and the possibility that prior experience with construction toys such as Lego is one of the determinants for graphical readership.