Data Analyses
For each single unit, a direction tuning curve is computed that
represents the mean firing rate (without baseline subtracted) at each
direction (orientation) tested. Click on the analysis names to
view the C source code for each analysis.
Bandwidth. Orientation tuning bandwidth (BW) was computed from
the direction tuning curve for each unit by first interpolating the
tuning curve at a one degree resolution using a Hanning (cosine)
window that had a half-width at half-height of 13.5 deg. The location
of the peak of the interpolated tuning curve was determined, and the
orientation angles closest to the peak for which the response fell to
1/sqrt(2) (or 70.7%) of the peak response on either side of the curve
were estimated. BW was defined as one-half of the difference between
these two angles. If the tuning curve never went below response
criterion, the BW was set to 180 deg.
Circular Variance. The circular variance (CV) was calculated
from orientation tuning curves as follows. Each point on the
orientation tuning curve is considered to be a vector where the
response amplitude is the vector length and the direction of motion is
the vector angle. The vector, S, that is the sum of all of the tuning
curve vectors is computed. The CV is the length of S divided by the
sum of all the response amplitudes. Note that CV averages the
responses for the two directions of motion at each orientation. If
the tuning curve is flat (response = C for all directions), then CV =
1. If an orientation-tuned neuron is so selective that its response is
non-zero for only one direction (or orientation) on the tuning curve,
then CV = 0.