• We have seen that one-tailed tests are used to determine if the mean of a sample is significantly greater than or less than a hypothesized value.

• Two-tailed tests are used to determine if the mean of a sample is significantly different from a hypothesized value.

• Null Universe: The neuron is not stimulus-driven. The Expected Value of \(X\) is 10 spikes per second.

• Alternative Universe: The neuron is stimulus-driven but the drive can be excitatory or inhibitory.

• We want to know which universe we are in.

• We write this as:

\[ \begin{align*} H_0 &: \mu_X = 10 \\ H_1 &: \mu_X \neq 10 \end{align*} \]

• Everything proceeds the same as for a one-tailed test until you get to the p-value calculation.

• At that stage, you must mirror the observed sample mean across the center of the null distribution and compute the area under the curve in both tails.