In Polygraph by Lepage and Brassard, several objects are used functionally in the play even while they are symbolic, not unusual when used by the author in a novel, play or even lyrics to a song.
The wall, at the start of the play, provides credits for the play, giving the sense of a film rather than a drama, as information is projected onto it. The wall is also used to separate places in the play. For example, literally it is used when David escapes from Berlin, climbing over the wall (representing the Berlin Wall). He successfully gains his freedom in this way, but not just from that portion of Germany. Symbolically, the wall offers separation and freedom from his relationship with Anna: a woman he leaves behind who feels sorrow for his departure, but who sensed he did not feel the way about her as she felt about him.
The wall provides divisions on the stage. Lucie performs her "Yorick" speech from Shakespeare's Hamlet "above and behind the wall." as if she is on a stage, performing. The wall also represents the train station.
The Metro station logo is...projected on the wall. The soundscape evokes a large, hollow-echoing Underground.
And at Francois' death, it is the barrier between life and death. The wall is used again to show the passage between the past and present. When Francois recalls the polygraph test he took when his friend Marie was found murdered, David comes over the wall—representing the memory—and they relive those moments. Coming into the present at Francois' restaurant represents Francois' flashback:
David enters the restaurant over the wall, sliding down with his back to it, his arms and his suit jacket spread like a giant, ominous spider.
Here the wall symbolizes Francois' desperate attempt to remove himself from harmful recollections surrounding Marie's death.
The polygraph is not only used to present a major conflict in the story...Francois' suspected guilt and his perception of this guilt lasting for years in his mind, but it also represents the question of honesty. This theme appears when the police refuse to tell Francois he is no longer a suspect. David continues keeping the truth from Francois when they meet six years later. It is ironic that the very machine used allegedly to ferret out the truth becomes symbolic of dishonestly, implicit not only in the system, but in the way David interacts with the world: he omits information, thereby deceiving others—even though he has noted that doing so can cause irreparable harm (as seen with Francois).
The camera is used to "project" a sense of watching a film rather than a play, so it is used to create a certain effect. Projections are used repeated throughout the story. However, it is also used to identify particular aspects of the play's plot development and themes. It is said that "the camera never lies," and in this case, it is used to expose various aspects of the play. Most significantly is the filming Lucie is involved in. At the beginning, she feels no emotional connection with her acting role. But when she learns it is based on Francois' dead friend, she is deeply affected.
...today I felt like they were taking me apart...Close-up of one eye, medium shot of the knife in the back, my right hand scratching at the floor...
When she sees a segment of filming:
(addressing the director offstage) This is from yesterday?
She starts to cry silently.
The camera is used to bring important details of the play to the audience's attention.