Trigonometry is one of the fundamental topics taught in high school and university curricula, but it is considered as one of the most challenging subjects for teaching and learning. In the current study Mason's theory of attention has been used to examine undergraduate student's perception of the transformation of sinusoidal functions. Two types of tasks--(A) Recognizing sinusoidal functions and (B) Assigning coordinates--were used in this study. The results show that undergraduate students participating in this study experienced difficulties in identifying a period of a sinusoid, especially when it was a fraction of [pi] radians. [For the complete proceedings, see ED583608.]