Seeing Two Rainforest Track Casts

Tracks at a Rainforest Field Station

At a rainforest field station, Anika and Mateo examine two plaster casts of animal footprints. One shows a tapir track, and the other shows a jaguar track. These are dried models, not living animals. Neither cast makes light. The team places each cast in its own covered viewing station. The stations have opaque walls that block outside light. Each has a low-brightness LED lamp, a cast holder, and an eye opening. Fixed hoods keep the lamps from shining straight into the observer's eyes. No one looks directly into a lamp.

The team compares four rounds. The lamps have equal brightness. Each cast stays in the same place, and the observer uses the same eye position at each station. The team changes the lamps or barriers as described in the record. After each change, the observer reports whether each cast is visible. A flap can block light between a lamp and its cast. A separate card can block the path between a cast and the eye opening. Both barriers are opaque.

Round 1: Both lamps are on. The lamp-to-cast and cast-to-eye paths are clear in both stations. The observer sees both casts.

Round 2: Both lamps stay on. An opaque flap blocks light from the tapir lamp from reaching the tapir cast. The jaguar station is unchanged. The observer does not see the tapir cast but sees the jaguar cast.

Round 3: The tapir flap is removed. Both lamps shine on their casts. An opaque card is placed between the jaguar cast and its eye opening. The observer sees the tapir cast but does not see the jaguar cast.

Round 4: The jaguar card is removed, leaving both paths clear. Both lamps are turned off. The observer does not see either cast.