# Tag Info

The index of sensitivity $d'$ is typically defined in terms of two equal variance normally distributed random variables with means $\mu_s$ and $\mu_n$ and standard deviation $\sigma$: $$d'=\frac{\mu_s-\mu_n}{\sigma}$$ In behavioural experiments, the probability that the subjects responded correctly (either saying 'yes' when the signal was present or saying ...
To calculate $d'$, you need to know two things: the hit rate and the false alarm rate. The hit rate is the proportion of trials where the stimulus was present and the subject responded that the stimulus was present. The false alarm rate is the proportion of trials where the stimulus was not present, and the subject responded that the stimulus was present. ...