fear-induced HPR: Trials with US+ cannot be used?

[amjh23]

Dear experts,
Do I understand correctly that the model for fear-induced heart period responses (HPR) in a fear conditioning experiment can only be applied to trials that do not contain a US+ presentation, because the arrival of the US+ would interfere with the signal produced by the CS+? And given this difficulty, can we use this model to analyze fear memory in the extinction phase (where there are no US)? Our CS+ (visual cue) is presented for 6 sec, the SOA between CS+ and US+ is 5.5 sec.
Many thanks for your help!

[dominikbach]

Thanks for reaching out!

1. The fear-conditioned HPR model has a US bias, i.e. CS estimates will be influenced by the presence of the US. This is because the CS-induced bradycardia peaks at the expected US time point. (It would probably also affect peak scoring schemes.). In consequence, US+ trials cannot be used to estimate the CS response.
2. When there is no US, as in extinction, the model can be used without problem.
3. The model has been tested for the timing settings that you use.

Dominik