In trace conditioning versus simultaneous conditioning, the CS ends before the US due to a gap, whereas in simultaneous conditioning the CS and UCS:

• A. Are presented at different times with no overlap.
• B. One after the other with a delay.
• C. Exactly at the same time and end together.
• D. The CS follows the US after a long delay.

Answer: (C)

Timing between the stimuli is what distinguishes these conditioning types. In trace conditioning there’s a gap after the CS ends before the US appears, so the association has to bridge that interval. In simultaneous conditioning, the CS and the US occur together with no offset, and they end at the same time, creating a tight, immediate pairing.

So, the best description is that the CS and US are presented exactly at the same moment and end together. This simultaneity means the animal learns that the CS and the US co-occur, with no temporal delay to bridge.

Other timing patterns involve offsets or delays between the stimuli, which describe different conditioning procedures and don’t fit simultaneous conditioning.