(A) Illustration of the model of direction-selective neurons, for a given
stimulus, in which there are m neurons whose preferred
directions point along each of the four cardinal directions. The correlation
structure is parametrized by c0,
cπ/2, and
cπ, the values of correlations in pairs
of neurons whose preferred directions differ by 0°, 90°, and
180°.
(B) Profiles of the percent improvement in coding accuracy as functions of
cπ/2 and
cπ, for different values of
m; in the cases m = 2, 3, and 5,
c0 was set to 0.2, comparable to the observed
values. Black dots represent the values observed in the data; the green dot
represents the average over all data. The gray area represents forbidden values
of the correlations (with negative eigenvalues of the covariance matrix).