= Orientation selectivity
{wiki}
<Orientation selectivity> is a systematic dependence of a visual <neuron>'s response on the axis of a bar, edge or stripe pattern presented in its <receptive field>, under specified stimulus conditions. Here the <angle> $\theta$ measures the stripe axis from horizontal: $0^\circ$ is horizontal and $90^\circ$ vertical. An axis has no arrow, so $\theta$ and $\theta+180^\circ$ describe the same orientation. A preference for one direction of movement across that axis is an additional property; the 1962 recordings included both equal and unequal responses to opposite movements. https://www.gatsby.ucl.ac.uk/teaching/courses/tn1-2020/additional/systems/JPhysiol-1962-Hubel-106-54.pdf[Hubel and Wiesel (1962), p. 112: orientation versus opposite movements]{ref}
A particularly clear experiment using <extracellular single-unit recording> appears in the 1959 paper, Figures 2–3. A bright $1^\circ\times8^\circ$ slit was centered on the same <receptive field> and rotated through successive <angles>; each presentation lasted one second. The vertical slit strongly increased the extracellularly recorded <spike train>, whereas the horizontal slit was ineffective. Small-spot tests had identified <ON and OFF receptive-field subregions>, with a central ON region and opposing flanks: rotation illuminated less of the center and more of the flanks. Geometry and location therefore mattered together. These dimensions belong to that recorded unit, not to every <neuron>. https://xbio-live.s3.amazonaws.com/narratives/57358/Hubel%20and%20Wiesel%201959_Guided%20paper.pdf[Hubel and Wiesel, Receptive fields of single neurones in the cat's striate cortex (1959), pp. 578–579, Figures 2–3: primary recordings]{ref}
An <orientation tuning curve> summarizes a controlled <angle> sweep. Keep location, size and <visual contrast> fixed; for a stripe pattern also specify <spatial frequency> and <phase>. The same <signed spatial filter model of a simple cell> can produce strong <orientation selectivity> and strong dependence on <phase>, as the following original toy illustrates. Its smooth curves are calculated predictions, not digitized or invented biological measurements.
\Image[/orientation-selectivity-angle-phase.png]
{title=<Orientation selectivity> and <phase> sensitivity in a toy <Gabor filter>}
{description=A chosen <Gaussian function> times a <cosine> supplies the signed filter. At fixed <phase> its normalized output peaks for vertical stripes; shifting the same stripes changes the signed drive and the rectified output. The <angle> labels refer to the stripe axis, perpendicular to the direction in which brightness varies. Spatial units and all parameters are arbitrary; curves use an infinite-domain <integral>, while the small image panels show only a crop. See <signed spatial filter model of a simple cell> for the calculation.}
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