= Orientation tuning curve
{title2=$r(\theta)$}
An <orientation tuning curve> plots a specified response against the stimulus-axis <angle> $\theta$, with the other stimulus variables controlled. A practical count summary for <extracellular single-unit recording> is
$$
\widehat r(\theta)=\frac{1}{mT}\sum_{k=1}^{m}N_k(\theta),
$$
where $N_k(\theta)$ counts <action potentials> in the same duration $T>0$ on trial $k$, and $m$ is the number of repeats at each <angle>. This estimates spikes per unit time in that window; the window must specify whether it covers onset, sustained stimulation, or both. Record a blank-background response separately, and report whether it has been subtracted. Randomizing <angle> order and repeating each condition helps separate <orientation selectivity> from changes over time, including <neural adaptation>. This is a proposed measurement procedure, not a claim that the original experiments used this estimator.
A <simple cell>'s <orientation tuning curve> can also change when the stimulus shifts. An <angle> sweep at fixed <phase>, a sweep averaging over <phase>, and a sweep of moving stripes ask different questions. Consequently, a single preferred <angle> does not specify the whole <receptive field>. The toy curve under <orientation selectivity> holds <phase> fixed and plots dimensionless output, rather than spikes per second.
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